CBSE Class 10 Science — Light — Reflection and Refraction

A convex lens of focal length $15\mathrm{cm}$, is forming a real image. If the size of image is same as the size of object, then position of object and position of image will be, respectively:

Rays from the sun converge at a point 25 cm behind a convex lens. The distance at which an object be placed in front of the lens to get a virtual image, is:

Rays from the sun converge at a point $25\text{ cm}$ behind a convex lens. The distance at which an object be placed in front of the lens to get a virtual image, is:

(a) Define absolute refractive index of an optical medium. (b) Table: Material Medium / Refractive Index — A: 1.50, B: 1.46, C: 1.31, D: 1.77. Arrange these material mediums given in the table in increasing order of speed of light through them.

The given figure shows image formation by a lens. Analyse the figure and answer the following questions: (a) What is the type of lens used for image formation in the given ray diagram? (b) If the real image is formed at a distance of $30\mathrm{cm}$ from the lens and the size of image is twice the size of the object, then where was the object placed?

When an incident ray of light enters in a medium 'X' from medium 'Y', it bends away from the normal. Comment about the following: (a) Speed of light in medium 'X' with respect to the speed of light in medium of 'Y'. (b) Optical density of medium 'X' with respect to the optical density medium 'Y'. Give reason for your answer in each case.

(a) Draw the ray diagram for refraction of light through a glass prism and mark angle of refraction and angle of deviation. (b) When the path of a light ray refracted through a glass prism is reversed how will the angle of deviation change? Explain.

An object of height 6 cm is placed at a distance of 30 cm from the optical centre of a concave lens of focal length 15 cm. Use lens formula to determine: (a) The distance of image from the optical centre. (b) The height of the image formed.

An object is placed at a distance of $30\text{ cm}$ in front of a convex lens of focal length $15\text{ cm}$. Use the lens formula to determine the position of the image. What will be the size of the image in this case?

(a) Draw the ray diagram for refraction of light through a glass prism and mark the angle of refraction and the angle of deviation. (b) When the path of a light ray refracted through a glass prism is reversed, how will the angle of deviation change? Explain.

Read the following passage and answer the questions given: Lenses can form different types of images depending upon their focal length and position of object. A convex lens can create real, inverted or virtual, erect images, while a concave lens forms only virtual and diminished images. The focal length determines the power of lens. Convex lenses have positive focal length while concave lenses have negative focal length by convention. When lenses are placed together, their combined power is determined by the sum of their individual powers. Ray diagrams help to visualize how light converges or diverges through lens to form an image. (a) A convex lens of focal length $20\mathrm{cm}$ is used to form an image. If an object is placed at $40\mathrm{cm}$ from the lens, what will be the position and nature of image? (b) Illustrate the formation of image with the help of ray diagram, when the object is placed between the optical centre and principal focus of concave lens. (c) (i) A lens combination consists of a convex lens of focal length $30\mathrm{cm}$ and a concave lens of focal length $15\mathrm{cm}$ placed together. Find the equivalent focal length and power of this lens combination. OR (c) (ii) Two lenses are placed in contact. One is a concave lens with focal length $2\mathrm{m}$ and the other is a convex lens with focal length $1.5\mathrm{m}$. What type of lens will the combination behave as (convex or concave)? Give reason.

Absolute refractive index of water and glass is $\frac{4}{3}$ and $\frac{3}{2}$ respectively. If the speed of light in glass is $2 \times 10^{8}\ \mathrm{m/s}$, the speed of light in water is :

If the absolute refractive indices of two media X and Y are $\frac{6}{5}$ and $\frac{4}{3}$ respectively, then the refractive index of Y with respect to X will be:

An object is placed at a distance of $30~\mathrm{cm}$ from the pole of a concave mirror. If its real and inverted image is formed at $60~\mathrm{cm}$ in front of the mirror, the focal length of the mirror is:

Mirror 'X' is used to concentrate sunlight in solar furnace and Mirror 'Y' is fitted on the side of the vehicle to see the traffic behind the driver. Which of the following statements are true for the two mirrors ? (i) The image formed by mirror 'X' is real, diminished and at its focus. (ii) The image formed by mirror 'Y' is virtual, diminished and erect. (iii) The image formed by mirror 'X' is virtual, diminished and erect. (iv) The image formed by mirror 'Y' is real, diminished and at its focus.

In the given figure the angle of incidence and the angle of deviation respectively are:

Assertion (A) : Silver chloride turns grey in sunlight. Reason (R) : Decomposition of silver chloride into silver and chlorine takes place by sunlight.

The values of absolute refractive indices of kerosene and water are 1.44 and 1.33 respectively. Compare the two media on the basis of their (a) optical density (b) mass density (c) relative speed of propagation of light. What do you infer on the basis of above comparisons?

An object is placed at a distance of $60\ cm$ from a concave lens of focal length $30\ cm$. Use lens formula to find the position of the image formed in this case.

(a) Out of the two lenses, one concave and the other convex, state which one will diverge a parallel beam of light falling on it. Draw a ray diagram to show the principal focus of the lens. OR (b) A ray of light after refraction from a convex lens emerges parallel to its principal axis. (i) Draw a labelled ray diagram to show it. (ii) In this case, the incident ray before refraction from the lens passes through a point on its principal axis. Name the point.

Draw ray diagrams to show the nature, position and relative size of the image formed by a convex mirror when the object is placed (i) at infinity and (ii) between infinity and pole P of the mirror.

A student placed a candle flame at different distances from a convex lens and focused its image on a screen. He recorded his observation in tabular form as given below: S.No. | Distance of flame (cm) | Distance of image (cm) 1 | -90 | +18 2 | -60 | +20 3 | -40 | +24 4 | -30 | +30 5 | -24 | +40 6 | -20 | +60 7 | -18 | +90 8 | -12 | +120 Analyse the observation table and on the basis of your analysis only, answer the following questions (without doing any calculations): (a) What is the focal length of the convex lens used? Give reason to justify your answer. (b) Which one of the sets of observations is not correct and why? (c) Draw ray diagram to show image formation for any correct set of observation.

A convex lens forms an $8.0\ \mathrm{cm}$ long image of a $2.0\ \mathrm{cm}$ long object which is kept at a distance of $6.0\ \mathrm{cm}$ from the optical centre of the lens. If the object and the image are on the same side of the lens, find (i) the nature of the image, (ii) the position of the image, and (iii) the focal length of the lens.

(a) (i) "In refraction of light through a rectangular glass slab, the emergent ray is always parallel to the direction of the incident ray." Why? Explain with the help of a ray diagram. What happens when a ray of light falls normally on one of the faces of a rectangular glass prism? Draw diagram. (ii) An object is placed at a distance of $30\ \mathrm{cm}$ from the optical centre of a concave lens of focal length $20\ \mathrm{cm}$. Use Lens formula to determine the position of the image formed in this case. OR (b) (i) A student wishes to study the image formation by a concave mirror using candle flame as object. State the type of the image formed by the mirror and mention the change in the image formed, if any, that he observes when the candle flame is gradually moved away from the pole of the mirror. Draw a ray diagram to show the image formation when the object distance is nearly equal to the radius of curvature of the mirror. (ii) A convex mirror used for rear-view on an automobile has a focal length of $3\cdot 0\ \mathrm{m}$. If a bus is located at $6\cdot 0\ \mathrm{m}$ from this mirror, use mirror formula to find the position of the image of the bus as seen in the mirror.

How will the image formed by a convex lens be affected, if the upper half of the lens is wrapped with a black paper ?

(a) State two laws of refraction of light. OR (b) Define the term absolute refractive index of a medium. A ray of light enters from vacuum to glass of absolute refractive index 1.5. Find the speed of light in glass. The speed of light in vacuum is $3 \times 10^{8} \mathrm{~m / s}$.

The heat produced at a point due to concentration of sunlight by a convex lens burns a paper. (a) Explain why it happens. (b) Name the term (in the context of the lens used) given to the point at which the paper starts burning. What does the bright spot formed on the paper represent?

(a) (i) Draw a ray diagram to show the path of the refracted ray in each of the following cases: A ray of light incident on a concave lens (1) parallel to its principal axis, and (2) is directed towards its principal focus. (ii) A 4 cm tall object is placed perpendicular to the principal axis of convex lens of focal length 24 cm. The distance of object from the lens is 16 cm. Find the position and size of image formed. OR (b) (i) Draw a ray diagram to show the path of the reflected ray in each of the following cases: A ray of light incident on a convex mirror (1) parallel to its principal axis, and (2) is directed towards its principal focus. (ii) A 1.5 cm tall candle flame is placed perpendicular to the principal axis of a concave mirror of focal length 12 cm. If the distance of the flame from the pole of the mirror is 18 cm, use mirror formula to determine the position and size of the image formed.

A highly polished surface such as a mirror reflects most of the light falling on it. In our daily life we use two types of mirrors — plane and spherical. The reflecting surface of a spherical mirrors may be curved inwards or outwards. In concave mirrors, reflection takes place from the inner surface, while in convex mirrors reflection takes place from the outer surface. (a) Define the principal axis of a concave mirror. (b) A ray of light is incident on a concave mirror, parallel to its principal axis. If this ray after reflection from the mirror passes through the principal axis from a point at a distance of $10 \mathrm{cm}$ from the pole of the mirror, find the radius of curvature of the mirror. (c) (i) An object is placed at a distance of $10 \mathrm{cm}$ from the pole of a convex mirror of focal length $15 \mathrm{cm}$. Find the position of the image. OR (c) (ii) A mirror forms a virtual, erect and diminished image of an object. Identify the type of this mirror. Draw a ray diagram to show the image formation in this case.

A student wants to obtain an erect image of an object using a concave mirror of $10 \text{ cm}$ focal length. What will be the distance of the object from mirror?

An object is placed in front of a convex mirror at infinity. According to the New Cartesian Sign Convention, the sign of the focal length and the sign of the image distance in this case are respectively :

(a) Complete the following ray diagram to show the formation of image: (b) Mention the nature, position and size of the image formed in this case. (c) State the sign of the image distance in this case using the Cartesian sign convention.

(a) A student has focussed the image of an object of height $3\text{ cm}$ on a white screen using a concave mirror of focal length $12\text{ cm}$. If the distance of the object from the mirror is $18\text{ cm}$, find the values of the following: (i) Distance of the image from the mirror (ii) Height of the image OR (b) Define power of a lens. The focal length of a lens is $-10\text{ cm}$. Write the nature of the lens and find its power. If an object is placed at a distance of $20\text{ cm}$ from the optical centre of this lens, according to the New Cartesian Sign Convention, what will be the sign of magnification in this case?

(a) An object is placed in front of a convex lens of focal length f. If the distance of the object from the lens is 2f, draw a ray diagram to show the formation of the image. Write the value of magnification in this case. (b) A student has focussed the image of a candle flame on a white screen using a convex lens. The situation is as given below: Length of the flame $= 2\text{ cm}$ Focal length of the lens $= 12\text{ cm}$ Distance of the flame from the lens $= 16\text{ cm}$ If the flame is perpendicular to the principal axis of the lens, calculate the values of the following: (i) Distance of the image from the lens (ii) Length of the image formed

Hold a concave mirror in your hand and direct its reflecting surface towards the sun. Direct the light reflected by the mirror on to a white card-board held close to the mirror. Move the card-board back and forth gradually until you find a bright, sharp spot of light on the board. This spot of light is the image of the sun on the sheet of paper; which is also termed as "Principal Focus" of the concave mirror. (a) List two applications of concave mirror. (b) If the distance between the mirror and the principal focus is $15 \mathrm{cm}$, find the radius of curvature of the mirror. (c) Draw a ray diagram to show the type of image formed when an object is placed between pole and focus of a concave mirror. OR (c) An object $10 \mathrm{cm}$ in size is placed at $100 \mathrm{cm}$ in front of a concave mirror. If its image is formed at the same point where the object is located, find: (i) focal length of the mirror, and (ii) magnification of the image formed with sign as per Cartesian sign convention.

A student took three concave mirrors of different focal lengths and performed the experiment to see the image formation by placing an object at different distances with these mirrors as shown in the following table. Table: | Case No. | Object-distance | Focal length | |---|---|---| | I | 45 cm | 20 cm | | II | 30 cm | 15 cm | | III | 20 cm | 30 cm | Now answer the following questions: (a) List two properties of the image formed in Case I. (b) In which one of the cases given in the table, the mirror will form real image of same size and why? (c) Name the type of mirror used by dentists. Give reason why do they use such type of mirrors. OR (c) Look at the table and identify the situation (object distance and focal length) which resembles the situation in which concave mirrors are used as shaving mirrors? Draw a ray diagram to show the image formation in this case.

OR When an object is kept within the focus of a concave mirror, an enlarged image is formed behind the mirror. This image is:

The laws of reflection hold true for:

A concave mirror is used for image formation for different positions of an object. What inferences can be drawn about the following when an object is placed at a distance of $10\text{ cm}$ from the pole of a concave mirror of focal length $15\text{ cm}$? (a) Position of the image (b) Size of the image (c) Nature of the image Draw a labelled ray diagram to justify your inferences.

What happens after refraction, when: (i) a ray of light parallel to the principal axis passes through a concave lens? (ii) a ray of light falls on a convex lens while passing through its principal focus? (iii) a ray of light passes through the optical centre of a convex lens?

Draw ray diagram in each of the following cases to show what happens after reflection to the incident ray when (a) it is parallel to the principal axis and falling on a convex mirror. (b) it is falling on a concave mirror while passing through its principal focus. (c) it is coming oblique to the principal axis and falling on the pole of a convex mirror.

The refractive index of a medium 'x' with respect to a medium 'y' is 2/3 and the refractive index of medium 'y' with respect to medium 'z' is 4/3. Find the refractive index of medium 'z' with respect to medium 'x'. If the speed of light in medium 'x' is $3 \times 10^8 \text{ ms}^{-1}$, calculate the speed of light in medium 'y'.

The diagram given below shows an object O and its image I. Without actually drawing the ray diagram, state the following : (i) Type of lens (Converging / Diverging) (ii) Name two optical instruments where such an image is obtained. (iii) List three characteristics of the image formed if this lens is replaced by a concave mirror of focal length 'f' and an object is placed at a distance 'f/2' in front of the mirror.

Draw a ray diagram in each of the following cases to show the formation of image, when the object is placed: (i) between optical centre and principal focus of a convex lens. (ii) anywhere in front of a concave lens. (iii) at 2F of a convex lens. State the signs and values of magnifications in the above mentioned cases (i) and (ii).

OR An object $4.0\text{ cm}$ in size, is placed $25.0\text{ cm}$ in front of a concave mirror of focal length $15.0\text{ cm}$. (i) At what distance from the mirror should a screen be placed in order to obtain a sharp image? (ii) Find the size of the image. (iii) Draw a ray diagram to show the formation of image in this case.

(a) A security mirror used in a big showroom has radius of curvature 5 m. If a customer is standing at a distance of 20 m from the cash counter, find the position, nature and size of the image formed in the security mirror. (b) Neha visited a dentist in his clinic. She observed that the dentist was holding an instrument fitted with a mirror. State the nature of this mirror and reason for its use in the instrument used by dentist. OR Rishi went to a palmist to show his palm. The palmist used a special lens for this purpose. (i) State the nature of the lens and reason for its use. (ii) Where should the palmist place/hold the lens so as to have a real and magnified image of an object? (iii) If the focal length of this lens is 10 cm and the lens is held at a distance of 5 cm from the palm, use lens formula to find the position and size of the image.

(a) A concave mirror of focal length 10 cm can produce a magnified real as well as virtual image of an object placed in front of it. Draw ray diagrams to justify this statement. (b) An object is placed perpendicular to the principal axis of a convex mirror of focal length 10 cm. The distance of the object from the pole of the mirror is 10 cm. Find the position of the image formed.

OR: (a) Define the following terms: (i) Power of a lens (ii) Principal focus of a concave mirror (b) Write the relationship among the object distance (u), image distance (v) and the focal length (f) of a (i) Spherical lens (ii) Spherical mirror (c) An object is placed at a distance of 10 cm from optical centre of a convex lens of focal length 15 cm. Draw a labelled ray diagram to show the formation of image in this case.

OR (a) A person suffering from myopia (near-sightedness) was advised to wear corrective lens of power $-2.5 \text{ D}$. A spherical lens of same focal length was taken in the laboratory. At what distance should a student place an object from this lens so that it forms an image at a distance of $10 \text{ cm}$ from the lens? (b) Draw a ray diagram to show the position and nature of the image formed in the above case.

(a) Draw a labelled ray diagram to show the path of a ray of light incident obliquely on one face of a glass slab. (b) Calculate the refractive index of the material of a glass slab. Given that the speed of light through the glass slab is $2 \times 10^8 \text{ m/s}$ and in air is $3 \times 10^8 \text{ m/s}$. (c) Calculate the focal length of a lens, if its power is $-2.5 \text{ D}$.

If the image formed by a spherical mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it? Draw a labelled ray diagram to support your answer.

State the laws of refraction of light. Explain the term ‘absolute refractive index of a medium’ and write an expression to relate it with the speed of light in vacuum.

What is meant by power of a lens? Write its SI unit. A student uses a lens of focal length 40 cm and another of -20 cm. Write the nature and power of each lens.

An object of height 4.0 cm is placed at a distance of 30 cm from the optical centre ‘O’ of a convex lens of focal length 20 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O’ and principal focus ‘F’ on the diagram. Also find the approximate ratio of size of the image to the size of the object.

An object is placed at a distance of 15 cm from a convex lens of focal length 20 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.

If the image formed by a lens for all positions of an object placed in front of it is always erect and diminished, what is the nature of this lens? Draw a ray diagram to justify your answer. If the numerical value of the power of this lens is 10 D, what is its focal length in the Cartesian system?

“A lens can form a magnified erect image as well as magnified inverted image of an object placed in front of it.” State the nature of this lens and draw ray diagrams to justify the above statement. Mark the positions of O, F and 2F in the diagram.

Analyse the following observation table showing variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations: (a) What is the focal length of the convex lens? Give reason to justify your answer. (b) Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion? (c) Select an appropriate scale and draw a ray diagram for the observation at S.No.2. Also find the approximate value of magnification.

Draw ray diagrams to show the formation of three times magnified (a) real, and (b) virtual image of an object by a converging lens. Mark the positions of O, F and 2F in each diagram.

(a) If the image formed by a mirror for all positions of the object placed in front of it is always diminished, erect and virtual, state the type of the mirror and also draw a ray diagram to justify your answer. Write one use such mirrors are put to and why. (b) Define the radius of curvature of spherical mirrors. Find the nature and focal length of a spherical mirror whose radius of curvature is + 24 cm.

Analyse the following observation table showing variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations : | S.No. | Object-Distance u (cm) | Image-Distance v (cm) | | :--- | :--- | :--- | | 1 | - 100 | + 25 | | 2 | - 60 | + 30 | | 3 | - 40 | + 40 | | 4 | - 30 | + 60 | | 5 | - 25 | + 100 | | 6 | - 15 | + 120 | (a) What is the focal length of the convex lens ? Give reason to justify your answer. (b) Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion ? (c) Select an appropriate scale and draw a ray diagram for the observation at S.No.2. Also find the approximate value of magnification.

A student very cautiously traces the path of a ray through a glass slab for different values of the angle of incidence ($\angle i$). He then measures the corresponding values of the angle of refraction ($\angle r$) and the angle of emergence ($\angle e$) for every value of the angle of incidence. On analysing these measurements of angles, his conclusion would be

Study the given ray diagrams and select the correct statement from the following:

A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen he should move the lens

A student very cautiously traces the path of a ray through a glass slab for different values of the angle of incidence (∠ i). He then measures the corresponding values of the angle of refraction (∠ r) and the angle of emergence (∠ e) for every value of the angle of incidence. On analysing these measurements of angles, his conclusion would be

A student focuses the image of a candle flame, placed at about 2 m from a convex lens of focal length 10 cm, on a screen. After that he moves gradually the flame towards the lens and each time focuses its image on the screen. (A) In which direction does he move the lens to focus the flame on the screen? (B) What happens to the size of the image of the flame formed on the screen? (C) What difference is seen in the intensity (brightness) of the image of the flame on the screen? (D) What is seen on the screen when the flame is very close (at about 5 cm) to the lens?

“The magnification produced by a spherical mirror is –3”. List four informations you obtain from this statement about the mirror/image.

The refractive indices of glass and water with respect to air are $3/2$ and $4/3$ respectively. If speed of light in glass is $2 \times 10^8$ m/s, find the speed of light in water.

The image of an object formed by a lens is of magnification – 1. If the distance between the object and its image is 60 cm, what is the focal length of the lens ? If the object is moved 20 cm towards the lens, where would the image be formed ? State reason and also draw a ray diagram in support of your answer.

(a) Define optical centre of a spherical lens. (b) A divergent lens has a focal length of 20 cm. At what distance should an object of height 4 cm from the optical centre of the lens be placed so that its image is formed 10 cm away from the lens. Find the size of the image also. (c) Draw a ray diagram to show the formation of image in above situation.

(a) Define focal length of a spherical lens. (b) A divergent lens has a focal length of 30 cm. At what distance should an object of height 5 cm from the optical centre of the lens be placed so that its image is formed 15 cm away from the lens? Find the size of the image also. (c) Draw a ray diagram to show the formation of image in the above situation.

It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm. (i) What should be the range of distance of an object placed in front of the mirror? (ii) Will the image be smaller or larger than the object. Draw ray diagram to show the formation of image in this case. (iii) Where will the image of this object be, if it is placed 24 cm in front of the mirror? Draw ray diagram for this situation also to justify your answer. Show the positions of pole, principal focus and the centre of curvature in the above ray diagrams.

In your laboratory you trace the path of light rays through a glass slab for different values of angle of incidence (∠i) and in each case measure the values of the corresponding angle of refraction (∠r) and angle of emergence (∠e). On the basis of your observations your correct conclusion is :

To determine the approximate value of the focal length of a given concave mirror, you focus the image of a distant object formed by the mirror on a screen. The image obtained on the screen, as compared to the object is always:

Suppose you have focused on a screen the image of candle flame placed at the farthest end of the laboratory table using a convex lens. If your teacher suggests you to focus the parallel rays of the sun, reaching your laboratory table, on the same screen, what you are expected to do is to move the:

In your laboratory you trace the path of light rays through a glass slab for different values of angle of incidence ($\angle i$) and in each case measure the values of the corresponding angle of refraction ($\angle r$) and angle of emergence ($\angle e$). On the basis of your observations your correct conclusion is:

An object of height 2.5 cm is placed at a distance of 15 cm from the optical centre ‘O’ of a convex lens of focal length 10 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O’, principal focus F and height of the image on the diagram.

List four characteristics of the images formed by plane mirrors.

To construct a ray diagram we use two rays of light which are so chosen that it is easy to determine their directions after reflection from the mirror. Choose these two rays and state the path of these rays after reflection from a concave mirror. Use these two rays to find the nature and position of the image of an object placed at a distance of 15 cm from a concave mirror of focal length 10 cm.

(a) State the laws of refraction of light. Explain the term absolute refractive index of a medium and write an expression to relate it with the speed of light in vacuum. (b) The absolute refractive indices of two media 'A' and 'B' are 2.0 and 1.5 respectively. If the speed of light in medium 'B' is $2 \times 10^8$ m/s, calculate the speed of light in: (i) vacuum, (ii) medium 'A'.

“A convex lens can form a magnified erect as well as magnified inverted image of an object placed in front of it.” Draw ray diagram to justify this statement stating the position of the object with respect to the lens in each case. An object of height 4 cm is placed at a distance of 20 cm from a concave lens of focal length 10 cm. Use lens formula to determine the position of the image formed.

Study the following diagram and select the correct statement about the device 'X':

A student has obtained a point image of a distant object using the given convex lens. To find the focal length of the lens he should measure the distance between the:

Four students P, Q, R and S traced the path of a ray of light passing through a glass slab for an angle of incidence 40° and measured the angle of refraction. The values as measured them were 18°; 22°; 25° and 30° respectively. The student who has performed the experiment methodically is

To find the image- distance for varying object- distances in case of a convex lens, a student obtains on a screen a sharp image of a bright object placed very far from the lens. After that he gradually moves the object towards the lens and each time focuses its image of the screen. (a) In which direction - towards or away from the lens, does he move the screen to focus the object? (b) What happens to the size of image - does it increase or decrease? (c) What happen when he moves the object very close to the lens?

“A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself.” Draw labelled ray diagram to justify the statement.

Mention the types of mirrors used as (i) rear view mirrors, (ii) shaving mirrors. List two reasons to justify your answers in each case.

An object of height 6 cm is placed perpendicular to the principal axis of a concave lens of focal length 5 cm. Use lens formula to determine the position, size and nature of the image if the distance of the object from the lens is 10 cm.

(a) State the laws of refraction of light. Give an expression to relate the absolute refractive index of a medium with speed of light in vacuum. (b) The refractive indices of water and glass with respect to air are 4/3 and 3/2 respectively. If the speed of light in glass is $2 \times 10^8$ $ms^{-1}$, find the speed of light in (i) air, (ii) water.

A student focussed the image of a distant object using a device ‘X’ on a white screen ‘S’ as shown in the figure. If the distance of the screen from the device is 40 cm, select the correct statement about the device.

A student obtained a sharp image of a burning candle, placed at the farther end of a laboratory table, on a screen using a concave mirror. For getting better value of focal length of the mirror, the subject teacher suggested him for focussing a well illuminated distant object. What should the student do?

After tracing the path of rays of light through a glass slab for three different angles of incidence, a student measured the corresponding values angle of refraction $r$ and angle of emergence $e$ and recorded them in the table given below. The correct observations are:

Select from the following the best set-up for tracing the path of a ray of light through a rectangular glass slab:

Study the following ray diagrams. The diagrams showing the correct path of the ray after passing through the lens are:

Out of the five incident rays shown in the figure find the three rays that are obeying the laws of refraction and may be used for locating the position of image formed by a convex lens:

To construct a ray diagram we use two light rays which are so chosen that it is easy to know their directions after refraction from the lens. List these two rays and state the path of these rays after refraction. Use these two rays to locate the image of an object placed between ‘f’ and ‘2f’ of a convex lens.

To construct ray diagram we use two light rays which are so chosen that it is easy to know their directions after reflection from the mirror. List these two rays and state the path of these rays after reflection. Use these rays to locate the image of an object placed between centre of curvature and focus of a concave mirror.

List four properties of the image formed by a plane mirror.

State the types of mirrors used for (i) headlights and (ii) rear view mirrors, in cars and motorcycles. Give reason to justify your answer in each case.

Name the type of mirror used in the following situations: (i) Headlights of a car (ii) Rear-view mirror of a vehicle (iii) Solar furnace. Support your answer with reason.

State the type of mirror preferred as (i) rear view mirror in vehicles, (ii) shaving mirror. Justify your answer giving two reasons in each case.

A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 24 cm. The distance of the object from the lens is 16 cm. Find the position, size and nature of the image formed, using the lens formula.

A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 24 cm. The distance of the object from the lens is 16 cm. Using lens formula, find the position, size and nature of the image formed.

The image of a candle flame placed at a distance of 45 cm from a spherical lens is formed on a screen placed at a distance of 90 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2 cm, find the height of its image.

List the new Cartesian sign convention for reflection of light by spherical mirrors. Draw a diagram and apply these conventions for calculating the focal length and nature of a spherical mirror which forms a 1/3 times magnified virtual image of an object placed 18 cm in front of it. OR With the help of a ray diagram, state what is meant by refraction of light. State Snell's law for refraction of light and also express it mathematically. The refractive index of air with respect to glass is 2/3 and the refractive index of water with respect to air is 4/3. If the speed of light in glass is $2 \times 10^8$ m/s, find the speed of light in (a) air, (b) water.

List the sign conventions that are followed in case of refraction of light through spherical lenses. Draw a diagram and apply these conventions in determining the nature and focal length of a spherical lens which forms three times magnified real image of an object placed 16 cm from the lens. OR State the laws of refraction of light. Write an expression to relate absolute refractive index of a medium with speed of light in vacuum. The refractive index of a medium ‘x’ with respect to ‘y’ is 2/3 and the refractive index of medium ‘y’ with respect to ‘z’ is 4/3. Calculate the refractive index of medium ‘z’ with respect of ‘x’.

List the sign conventions for reflection of light by spherical mirrors. Draw a diagram and apply these conventions in the determination of focal length of a spherical mirror which forms a three times magnified real image of an object placed 16 cm infront of it. Or State the law of refraction of light that defines the refractive index of a medium with respect to the other. Express it mathematically. How is refractive index of any medium ‘A’ with respect to a medium ‘B’ related to the speed of propagation of light in two media A and B ? State the name of this constant when one medium is vacuum or air. The refractive indices of glass and water with respect to vacuum are 3/2 and 4/3 respectively. If the speed of light in glass is $2 \times 10^8$ m/s, find the speed of light in (i) vacuum, (ii) water.

To determine focal length of a concave mirror a student obtains the image of a well lit distant object on a screen. To determine the focal length of the given concave mirror he needs to measure the distance between :

Parallel light rays from a distant object incident on a device 'X' form a point size image on a screen. The device 'X' must be

A student has to determine the focal length of a concave mirror by obtaining the image of a distant object on a screen. For getting best result he should focus

A student has to determine the focal length of a convex lens by obtaining the image of a distant object on a screen. Which of the following measures should he take to obtain better results? a. Select a lens of small diameter (say 3 cm). b. Select a lens of larger diameter (say 5 cm). c. Select an object very far from the lens. d. Select an object far, but not very far, from the lens. e. Keep all the lights of the room on. f. Keep minimum lights of the room on.

A student obtained a sharp image of the grills of a window on a screen using a concave mirror. His teacher remarked that for getting better results a well lit distant object (preferably the sun) should be focussed on the screen. What should be done for this purpose?

A student obtained a sharp inverted image of a distant tree on a screen placed in front of the concave mirror. He then removed the screen and tried to look into the mirror. He would now see

If you are to determine the focal length of a convex lens, you should have

To determine the focal length of a convex lens by obtaining a sharp image of a distant object we generally follow the following steps which are not in proper sequence. (a) Hold the lens between the object and the screen (b) Measure the distance between the lens and the screen (c) Select a well lit distant object (d) Place a screen opposite to the object on the lab table (e) Adjust the position of the lens to form a sharp image. The correct sequence of these steps is :

Three students X, Y and Z are finding the focal length of the given concave mirror by obtaining the image of the object selected by them. X obtains the image of the grill of the nearest window of the lab. Y obtains the image of a white painted building near the lab and Z obtains a point size image of the sun. The most correct value of the focal length is obtained by

While performing the experiment on tracing the path of a ray of light through a rectangular glass slab, in which of the following experimental set-ups is a student likely to get best results ? $P_1$ and $P_2$ are the positions of pins fixed by him.

A student traces the path of a ray of white light through a rectangular glass slab and marks, the angles of incidence (∠i), refraction (∠r) and emergence (∠e) as shown. Which angle or angles has he not marked correctly ?

The values of ∠i, ∠r and ∠e as measured by four students P, Q, R and S are tabulated below: The student who performed the experiment most carefully and methodically is

Four students showed the following traces of the path of a ray of light passing through a rectangular glass slab. The trace most likely to be correct is that of student

While tracing the path of a ray of light passing through a rectangular glass slab a student tabulated his observations as given below : | S. No. | ∠i | ∠r | ∠e | | :--- | :--- | :--- | :--- | | I | 60° | 40° | 61° | | II | 50° | 36° | 51° | | III | 40° | 28° | 39° | | IV | 30° | 20° | 31° | The correct observation is :

While performing the experiment on tracing the path of a ray of light through a rectangular glass slab, in which of the following experimental set-ups is a student likely to get best results? (P₁ and P₂ are the positions of the pins fixed for the experiment)

Define and show on a diagram, the following terms relating to a concave mirror : (i) Aperture (ii) Radius of curvature

With the help of a ray diagram explain why a convex mirror is preferred for rear view mirrors in motor cars.

An object is placed between infinity and the pole of a convex mirror. Draw a ray diagram and also state the position, the relative size and the nature of the image formed.

Draw the ray diagram and also state the position, the relative size and the nature of image formed by a concave mirror when the object is placed at the centre of curvature of the mirror.

What is understood by lateral displacement of light? Illustrate it with the help of a diagram. List any two factors on which the lateral displacement in a particular substance depends.

Define, 'refractive index of a transparent medium.' What is its unit? Which has a higher refractive index, glass or water?

What is the principle of reversibility of light ? Show that the incident ray of light is parallel to the emergent ray of light when light falls obliquely on a side of a rectangular glass slab.

(a) Under what condition will a glass lens placed in a transparent liquid become invisible ? (b) Describe and illustrate with a diagram, how we should arrange two converging lenses so that a parallel beam of light entering one lens emerges as a parallel beam after passing through the second lens. (c) An object is placed at a distance of $3\text{ cm}$ from a concave lens of focal length $12\text{ cm}$. Find the (i) position and (ii) nature of the image formed. OR (a) With the help of a ray diagram explain why a concave lens diverges the rays of a parallel beam of light. (b) A $2.0\text{ cm}$ tall object is placed perpendicular to the principal axis of a concave lens of focal length $15\text{ cm}$. At what distance from the lens, should the object be placed so that it forms an image $10\text{ cm}$ from the lens ? Also find the nature and the size of image formed.

(a) If the image formed by a lens is diminished in size and erect, for all positions of the object, what type of lens is it? (b) Name the point on the lens through which a ray of light passes undeviated. (c) An object is placed perpendicular to the principal axis of a convex lens of focal length $20\text{ cm}$. The distance of the object from the lens is $30\text{ cm}$. Find (i) the position (ii) the magnification and (iii) the nature of the image formed. OR (a) One-half of a convex lens is covered with a black paper. Will such a lens produce an image of the complete object? Support your answer with a ray diagram. (b) An object $5\text{ cm}$ high is held $25\text{ cm}$ away from a converging lens of focal length $10\text{ cm}$. (i) Draw the ray diagram and (ii) Calculate the position and size of the image formed. (iii) What is the nature of the image?

(a) What is meant by 'power of a lens' ? (b) State and define the S.I. unit of power of a lens. (c) A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in close contact with each other. Calculate the lens power of this combination. OR (a) Draw a ray diagram to show the formation of image of an object placed between infinity and the optical centre of a concave lens. (b) A concave lens of focal length 15 cm forms an image 10 cm from the lens. Calculate (i) the distance of the object from the lens (ii) the magnification for the image formed (iii) the nature of the image formed

To find the focal length of a concave mirror, Sita should choose which one of the following set-ups ?

To find the focal length of a concave mirror Rahul focuses a distant object with this mirror. The chosen object should be:

Dhoni obtained the image of a distant object on a screen by using a concave mirror. To find the focal length of the mirror he should measure the distance between

For finding the focal length of a convex lens by obtaining the image of a distant object, one should use as the object:

By using a convex lens, a student obtained a sharp image of his class-room window grill on a screen. In which direction should he move the lens to focus a distant tree instead of the grill ?

Which of the following can be used to find the focal length of a convex lens ?

Mohan, Sohan and Rahul separately measured the focal length of the same convex lens using the same distant tree as object. All of them measured the distance between the lens and the inverted image of the tree on the screen. Mohan obtained a sharp image on the screen and labelled the measured distance as $f_1$. Sohan obtained a slightly smaller and somewhat blurred image on the screen. He labelled the measured distance as $f_2$. Rahul obtained a slightly magnified and blurred image on the screen. He labelled the measured distance as $f_3$. The three measured values of focal length are likely to be related as

To determine the focal length of a convex lens by obtaining a sharp image of a distant object, the following steps were suggested which are not in proper sequence : I. Hold the lens between the object and the screen. II. Adjust the position of the lens to form a sharp image. III. Select a suitable distant object. IV. Measure the distance between the lens and the screen. The correct sequence of steps to determine the focal length of the lens is

Mohan obtained a sharp inverted image of a distant tree on the screen placed behind the lens. He then moved the screen and tried to look through the lens in the direction of the object. He would see:

In these diagrams, the angle of refraction $r$ has been correctly marked in which diagram ?

Four students A, B, C and D traced the paths of incident ray and the emergent ray by fixing pins P and Q for incident ray and pins R and S for emergent ray for a ray of light passing through a glass slab. The correct emergent ray was traced by the student:

The best set-up of pins for the incident ray to trace the path of a ray of light through a rectangular glass slab is represented in the figure

Rahim recorded the following sets of observations while tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. $$\begin{array}{|c|c|c|c|} \hline \text{S. No.} & \text{Angle of incidence} & \text{Angle of refraction} & \text{Angle of emergence} \\ \hline \text{I} & 45^\circ & 41^\circ & 45^\circ \\ \hline \text{II} & 40^\circ & 38^\circ & 38^\circ \\ \hline \text{III} & 45^\circ & 41^\circ & 40^\circ \\ \hline \text{IV} & 41^\circ & 45^\circ & 41^\circ \\ \hline \end{array}$$ The correct observation is recorded at serial number:

While tracing the path of a ray of light through a rectangular glass slab, the four students I, II, III and IV arrived at the following different conclusions : Student I : Angle of incidence > Angle of emergence. Student II : Angle of refraction > Angle of emergence. Student III : Emergent ray is parallel to refracted ray. Student IV : Emergent ray is parallel to incident ray. The correct conclusion has been drawn by the student

For a ray of light passing through a glass slab the lateral displacement was correctly measured as

Explain why a ray of light passing through the centre of curvature of a concave mirror gets reflected along the same path.

What is the nature of the image formed by a concave mirror if the magnification produced by the mirror is + 3 ?

At what distance should an object be placed from a convex lens of focal length 18 cm to obtain an image at 24 cm from it on the other side. What will be the magnification produced in this case ?