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?
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?
The lens is a convex lens. Since the image is erect and diminished, the lens must be a convex lens. The ray diagram for this lens is shown below:
The focal length of the lens can be calculated using the formula: Power (D) = 1/focal length (m). Given that the power of the lens is 10 D, we can calculate the focal length as follows: focal length = 1/10 = 0.1 m = 10 cm.
Marking Scheme
- 1Nature of lens (1 mark)
- 2Ray diagram (1 mark)
- 3Focal length calculation (1 mark)
Hint
Use the formula: Power (D) = 1/focal length (m) to calculate the focal length.
Quick Oral Answer
The lens is a convex lens because it forms an erect and diminished image for all positions of the object. The focal length of the lens can be calculated using the formula: Power (D) = 1/focal length (m).
Analysis & Explanation
The lens is a convex lens because it forms an erect and diminished image for all positions of the object. The ray diagram shows that the lens is convex. The focal length of the lens can be calculated using the formula: Power (D) = 1/focal length (m).
Common Mistakes
- 1Incorrectly identifying the lens as concave
- 2Incorrectly drawing the ray diagram
- 3Incorrectly calculating the focal length
Interesting Facts
Convex lenses are commonly used in magnifying glasses and microscopes.
The focal length of a convex lens is always positive.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2017?
This question carries 3 marks in the CBSE Class 10 Science 2017 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Light — Reflection and Refraction" in the CBSE Class 10 Science syllabus.
What type of question is this in the CBSE Class 10 Science 2017 paper?
This is a Short Answer question from Section A in the CBSE Class 10 Science 2017 paper.