lenses MCQs for UPSC Prelims

27 practice questions on lenses from the Light: Mirrors and Lenses section of the UPSC Prelims syllabus. 27 come with a written explanation. Try the sample set below - the answer stays hidden until you ask for it.

8 Easy 14 Medium 5 Hard

Sample questions

Q1
easy
A concave lens is
  1. A of the same thickness at every point
  2. B thinner in the middle and thicker at the edges
  3. C thicker in the middle and thinner at the edges
  4. D always thicker at one edge than at the other
Show answer and explanation

Correct answer: B - thinner in the middle and thicker at the edges

A concave lens is hollowed on both faces, so the middle is its thinnest part and the rim is thicker. The second option describes a convex lens. Equal thickness everywhere describes a plain glass sheet, and a lens is not made lopsided from edge to edge.
Q2
medium
A convex lens gives a virtual, erect and enlarged image when the object is placed
  1. A very close to the lens
  2. B behind the screen
  3. C very far from the lens
  4. D exactly where the screen stands
Show answer and explanation

Correct answer: A - very close to the lens

Only when the object is close to a convex lens does it act as a magnifying glass and give an enlarged upright image. A distant object gives a real inverted image instead. The screen catches the image and is not a place for the object, so the last two options make no sense.
Q3
medium
A convex lens held in a dark room forms a sharp image of a bright window on the opposite wall. That image of the window is
  1. A virtual
  2. B inverted
  3. C erect
  4. D exactly as large as the real window
Show answer and explanation

Correct answer: B - inverted

The window is far from the lens, so the lens forms a real image on the wall, and every real image formed by a convex lens is upside down. It is much smaller than the window itself, not equal in size. An image that falls on a wall is real and cannot be virtual.
Q4
medium
The lens of a simple camera forms a picture on the film or sensor at the back. That lens is
  1. A concave, because it forms a virtual image
  2. B a plane sheet, because it does not bend light
  3. C convex, because it can form a real image
  4. D a convex mirror that reflects the scene inwards
Show answer and explanation

Correct answer: C - convex, because it can form a real image

A camera needs a real image formed on the film or sensor, and only a converging convex lens can do that. A concave lens gives a virtual image that no film could record. A plane sheet forms no image at all, and a mirror would send the light back out of the camera.
Q5
easy
A watch repairer holds a small lens close to the eye to see the tiny parts of a watch clearly. This lens is
  1. A a convex lens
  2. B a plane mirror
  3. C a flat piece of clear glass
  4. D a concave lens
Show answer and explanation

Correct answer: A - a convex lens

A convex lens held close to a small object gives an enlarged upright image, which is exactly what the repairer needs. A concave lens would make the parts look even smaller. A flat piece of glass magnifies nothing, and a mirror would reflect the light away instead of letting the eye look through.
Q6
easy
A convex lens is also known as
  1. A a scattering lens
  2. B a converging lens
  3. C a diverging lens
  4. D a reflecting lens
Show answer and explanation

Correct answer: B - a converging lens

A convex lens brings parallel rays of light together at a point, so it is called converging. A diverging lens spreads rays apart, which is what a concave lens does. Scattering happens at rough surfaces, and reflecting describes mirrors.
Q7
easy
A lens that is thicker in the middle than at its edges is called
  1. A a concave lens
  2. B a convex lens
  3. C a plane glass slab
  4. D a spherical mirror
Show answer and explanation

Correct answer: B - a convex lens

A convex lens bulges outwards on both faces, so its middle is the thickest part. A concave lens is the opposite, being thinnest in the middle. A plane slab has the same thickness everywhere, and a mirror reflects light instead of letting it through.
Q8
medium
Consider these statements. Statement I: A convex lens is thicker at its centre than at its edges. Statement II: A lens works by reflecting light back from its front surface.
  1. A Both statements are wrong
  2. B Only Statement I is correct
  3. C Only Statement II is correct
  4. D Both statements are correct
Show answer and explanation

Correct answer: B - Only Statement I is correct

Statement I describes the shape of a convex lens correctly. Statement II is wrong, because a lens is transparent and works by bending light that passes through it, while reflecting light back is the work of a mirror. Only the first statement holds.

Practice all 27 lenses questions free

Timed practice, instant scoring, and explanations for every question. Free forever - no card, no catch.

Start practicing I am a teacher - create a test

More Light: Mirrors and Lenses topics

spherical-mirrors 28