CBSE CLASS 10 · MATHS & SCIENCE

Class 10 Light MCQ Practice

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SCIENCE / CLASS 105 QUESTIONS

1/f = 1/v − 1/u

LIGHT · LENSES · MIRRORS

Make sense of light.

Get your signs right, choose a formula and see what the answer means.

5 questions4 ideas to exploreHints if you need them

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Optics: signs, formulas and units — TutorMax original questions

Assign directed distances

For incident light travelling left to right, rightward distances are positive. Use the mirror pole or lens optical centre as the origin.

Choose the device formula

Mirror: 1/f=1/v+1/u. Lens: 1/f=1/v−1/u. Rearrange before substituting signed values.

Interpret magnification

For a lens, m=v/u. A negative value means inversion. The magnitude gives relative image height, not position.

Convert lens-power units

P=1/f with f in metres gives dioptres. A centimetre focal length must be divided by 100 first.

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Optics: signs, formulas and units — TutorMax original questions

Assign directed distances: For incident light travelling left to right, rightward distances are positive. Use the mirror pole or lens optical centre as the origin.

Choose the device formula: Mirror: 1/f=1/v+1/u. Lens: 1/f=1/v−1/u. Rearrange before substituting signed values.

Interpret magnification: For a lens, m=v/u. A negative value means inversion. The magnitude gives relative image height, not position.

Convert lens-power units: P=1/f with f in metres gives dioptres. A centimetre focal length must be divided by 100 first.

Light travels left to right. An object is 36 cm left of a lens. What is its Cartesian object distance u?

−36 cm
+36 cm
−0.36 cm

Let’s work through the answer

Measure from the optical centre. The object lies 36 cm in the negative direction, so u=−36 cm.

A concave mirror has f=−12 cm and u=−36 cm. Find v using 1/f=1/v+1/u.

−18 cm
+18 cm
−9 cm

Let’s work through the answer

1/v=1/f−1/u=−1/12+1/36=−1/18. Thus v=−18 cm.

A convex lens has f=+12 cm and u=−36 cm. Find v using 1/f=1/v−1/u.

+18 cm
−18 cm
+9 cm

Let’s work through the answer

For a lens, 1/v=1/f+1/u=1/12−1/36=1/18. Thus v=+18 cm.

A lens has u=−36 cm and v=+18 cm. What does m=v/u tell you?

m=−0.5: inverted, half-height
m=+0.5: upright, half-height
m=−2: inverted, double-height

Let’s work through the answer

m=18/(−36)=−0.5. Negative means inverted; |m|=0.5 means half-height.

A convex lens in air has f=+40 cm. What is its power?

+2.5 D
+0.025 D
−2.5 D

Let’s work through the answer

+40 cm=+0.40 m. P=1/f=1/0.40=+2.5 D.

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About this preview & your answers

These are original TutorMax practice questions, not official board-paper questions. We’re still checking their fit with the 2026–27 syllabus. Five questions give us a starting point, not a predicted board grade or a complete picture of a chapter.

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