If you are to determine the focal length of a convex lens, you should have
If you are to determine the focal length of a convex lens, you should have
Options
Official answer
To determine the focal length of a convex lens, a student must have a convex lens, a screen, holders for both of them, and a measuring scale.
Marking scheme
- 1.Identification of all essential apparatus (lens, screen, holders, and scale) (1 mark)
Hint
Think about how you will keep the lens and screen stable during the experiment and how you will measure the distance between them.
Quick oral answer
We use a distant object because the rays coming from infinity are parallel to the principal axis and, after refraction through the convex lens, converge at its focus, allowing us to measure the focal length directly as the distance between the lens and the screen.
Common mistakes
- 1.Choosing options that lack a measuring scale or holders, which are essential for accurate experimental measurement.
Analysis and explanation
To experimentally determine the focal length of a convex lens (for example, by focusing a distant object to form a sharp image on a screen), the following apparatus is required:
- Convex Lens: The refracting optical element under study.
- Screen: To receive the real and inverted image of the distant object.
- Holders: To keep both the lens and the screen stable, upright, and aligned along the same principal axis.
- Scale: To measure the distance between the center of the lens and the screen, which corresponds to the focal length .
- Option A is incorrect because without holders and a scale, the components cannot be aligned stably or measured.
- Option B is incorrect because it lacks a screen to capture the image and a scale to measure the distance.
- Option C is incorrect because the lens and screen themselves are missing.
Interesting facts
The method of focusing a distant object on a screen gives an approximate focal length because the light rays coming from a very distant object are assumed to be parallel to the principal axis, converging exactly at the principal focus.
Question details
Q33 of 41 questions
- Board
- CBSE
- Class
- Class 10
- Subject
- Science
- Year
- 2012
- Section
- Section B
- Marks
- 1
- Type
- MCQ
- Chapter
- Light — Reflection and Refraction
- Topic
- Focal Length of a Convex Lens
- Bloom's level
- Understanding
- Syllabus topic
- Refraction of light by spherical lenses
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Frequently asked questions
How many marks does this question carry in CBSE Class 10 Science 2012?
This question carries 1 mark in the CBSE Class 10 Science 2012 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 topic does this question cover in Science?
This question covers the topic "Focal Length of a Convex Lens" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2012 paper?
This is a MCQ question from Section B in the CBSE Class 10 Science 2012 paper.