CBSE Class 10 Science • Light and Image Formation
Light Reflection and Refraction Class 10 Worksheet with Answers
Why does a spoon appear bent in water? How can a concave mirror form both enlarged and diminished images? Practise these concepts with the Light Reflection and Refraction Class 10 worksheet with answers. Revise spherical mirrors, lenses, refractive index, sign conventions, magnification and lens power.
This chapter combines explanations, ray diagrams and numerical calculations. Understanding how a ray changes direction helps you predict an image before using a formula. Checking that prediction against your numerical answer is a useful way to catch sign errors.
Begin with our Light Reflection and Refraction Class 10 notes and mind map . Then attempt the worksheet independently and use the answers to review your working, units and descriptions of image formation.
Light Reflection and Refraction Class 10 Summary
Reflection of Light
Reflection is the return of light into the same medium after striking a surface. The angle of incidence equals the angle of reflection. The incident ray, reflected ray and normal at the point of incidence lie in the same plane.
Measure Angles from the Normal
The normal is perpendicular to the surface at the point of incidence. Reflection and refraction angles are measured from this normal, not from the surface.
Refraction of Light
Refraction occurs when light passes between media in which its speed differs. At oblique incidence, this usually changes the ray’s direction. Light entering an optically denser medium bends towards the normal; light entering an optically rarer medium bends away from it.
At normal incidence, the speed can change without a change in direction. Optical density concerns light’s speed and should not be confused with mass density.
Spherical Mirrors: Concave and Convex
A concave mirror has an inward-curving reflecting surface. A convex mirror has an outward-curving reflecting surface. Important terms include pole P, principal axis, centre of curvature C, principal focus F, focal length f and radius of curvature R.
For a spherical mirror in the paraxial approximation: R = 2f.
A concave mirror can form real or virtual images depending on object position. A convex mirror forms a virtual, erect and diminished image of a real object.
Concave Mirror Image Formation
| Object position | Image position | Nature and size |
|---|---|---|
| At infinity | At F | Real, inverted and highly diminished. |
| Beyond C | Between C and F | Real, inverted and diminished. |
| At C | At C | Real, inverted and the same size. |
| Between C and F | Beyond C | Real, inverted and enlarged. |
| At F | At infinity | Reflected rays emerge parallel. |
| Between F and P | Behind the mirror | Virtual, erect and enlarged. |
Convex and Concave Lenses
A convex lens is thicker at its centre and generally converges parallel light rays when surrounded by air. A concave lens is thinner at its centre and generally diverges them. A thin lens has an optical centre O and principal foci on both sides.
| Object position | Image position | Nature and size |
|---|---|---|
| At infinity | At F₂ | Real, inverted and highly diminished. |
| Beyond 2F₁ | Between F₂ and 2F₂ | Real, inverted and diminished. |
| At 2F₁ | At 2F₂ | Real, inverted and the same size. |
| Between F₁ and 2F₁ | Beyond 2F₂ | Real, inverted and enlarged. |
| At F₁ | At infinity | Refracted rays emerge parallel. |
| Between F₁ and O | On the same side as the object | Virtual, erect and enlarged. |
A concave lens forms a virtual, erect and diminished image of a real object. For an object at a finite distance, the image lies between the optical centre and the focus on the object’s side.
Light Class 10 Formulas and Sign Convention
| Quantity | Formula | Remember |
|---|---|---|
| Mirror formula | 1/f = 1/v + 1/u | Use signed distances. |
| Mirror magnification | m = hᵢ/hₒ = −v/u | The minus sign is essential. |
| Thin lens formula | 1/f = 1/v − 1/u | Different from the mirror formula. |
| Lens magnification | m = hᵢ/hₒ = v/u | No additional minus sign. |
| Absolute refractive index | n = c/s | s is light’s speed in the medium; n has no unit. |
| Snell’s law | n₁ sin i = n₂ sin r | Angles are measured from the normal. |
| Lens power | P = 1/f | Use f in metres; power is in dioptres. |
Apply the Cartesian Sign Convention
Measure mirror distances from the pole and lens distances from the optical centre. Distances measured in the direction of incident light are positive; those measured opposite to it are negative. Heights above the principal axis are positive and those below it are negative.
For the usual diagrams with incident light travelling from left to right, a real object on the left has u < 0. A concave mirror has f < 0, a convex mirror f > 0, a convex lens f > 0 and a concave lens f < 0.
Light Reflection and Refraction Class 10 Numericals
Example 1: Concave Mirror
An object is placed 30 cm in front of a concave mirror of focal length 15 cm. Find the image position.
u = −30 cm
f = −15 cm
1/f = 1/v + 1/u
1/v = 1/f − 1/u
1/v = −1/15 + 1/30
1/v = −1/30
v = −30 cm
m = −v/u
m = −(−30)/(−30)
m = −1
Answer: The image forms 30 cm in front of the mirror. It is real, inverted and the same size as the object.
Example 2: Convex Lens
An object is placed 30 cm from a convex lens of focal length 20 cm. Find the image position and magnification.
u = −30 cm
f = +20 cm
1/f = 1/v − 1/u
1/v = 1/f + 1/u
1/v = 1/20 − 1/30
1/v = 1/60
v = +60 cm
m = v/u
m = 60/(−30)
m = −2
Answer: The image forms 60 cm on the opposite side of the lens. It is real, inverted and twice the object’s size.
Example 3: Power of a Concave Lens
Find the power of a concave lens with focal length 25 cm.
f = −25 cm
f = −0.25 m
P = 1/f
P = 1/(−0.25)
P = −4 D
Answer: The power is −4 dioptres. Negative power indicates a diverging lens.
Ray Diagrams Class 10: How to Practise
- Start with labels: draw the principal axis and mark the pole or optical centre, foci and other reference points.
- Use two standard rays: draw them from the same point on the object.
- Show direction: add arrowheads to incident, reflected or refracted rays.
- Locate a real image: use the point where the outgoing rays actually meet.
- Locate a virtual image: extend the outgoing rays backwards using dashed lines.
- Describe the result: state position, size, orientation and whether the image is real or virtual.
Useful Standard Rays
For a concave mirror, a ray parallel to the principal axis reflects through the focus. A ray through the centre of curvature retraces its path.
For a convex lens, a parallel ray refracts through the principal focus on the opposite side. A ray through the optical centre of a thin lens passes approximately undeviated.
Light Reflection and Refraction Class 10 MCQs with Answers
1. Which mirror gives a wide field of view and a diminished image?
A. Concave mirror
B. Convex mirror
C. Plane mirror
D. All mirrors equally
Answer: B. Convex mirror. It forms an erect, diminished image and provides a wide field of view.
2. What is the power of a convex lens with focal length 50 cm?
A. +2 D
B. −2 D
C. +0.02 D
D. −0.02 D
Answer: A. +2 D. The focal length is +0.50 m, so P = 1/0.50 = +2 D.
3. What does negative magnification indicate?
A. An erect image
B. An inverted image
C. No image
D. Always a diminished image
Answer: B. An inverted image. Image size depends on the magnitude of magnification, not its sign alone.
Assertion–Reason Practice
Assertion: Light entering glass from air at oblique incidence bends towards the normal.
Reason: Light travels more slowly in ordinary glass than in air.
Answer: Both statements are true, and the reason explains the assertion through the laws of refraction.
Light Class 10 Case-Based Questions
Case Study: A Convex Lens as a Magnifier
A student views small printed letters through a convex lens. The page is placed between the lens and its principal focus. The letters appear upright and enlarged.
Question 1: What is the nature of the image?
Virtual, erect and enlarged.
Question 2: On which side does the image form?
On the same side of the lens as the object.
Question 3: Can this image be obtained directly on a screen?
No. The outgoing rays do not actually converge at the
apparent image position.
Important Questions and Chapter-Test Practice
- State the laws of reflection and refraction.
- Define principal focus, focal length and refractive index.
- Compare real and virtual images.
- Draw image-formation diagrams for concave mirrors and convex lenses.
- Explain the uses of convex mirrors and concave mirrors.
- Solve mirror and lens numericals using signed distances.
- Calculate magnification and interpret its sign and magnitude.
- Calculate lens power after converting focal length into metres.
Check Your Numerical Answer
Write the given values with signs, select the correct formula and show one calculation step per line. Include units in the final answer. Then compare the calculated image position and magnification with the expected ray diagram.
Use the worksheet as a chapter test, then revise errors under formulas, signs, units or image formation before attempting those questions again.
Frequently Asked Questions
What is the difference between reflection and refraction?
Reflection returns light into the same medium. Refraction occurs as light passes between media with different light speeds and usually changes direction at oblique incidence.
Does light always bend when it enters another medium?
No. At normal incidence, light can change speed without changing direction. Bending also depends on whether the media have different refractive indices.
Why are mirror and lens magnification formulas different?
Reflection and transmission produce different geometrical relationships under the same Cartesian convention. Use m = −v/u for mirrors and m = v/u for lenses.
Can a concave mirror form a virtual image?
Yes. When a real object lies between the pole and focus, the image is virtual, erect and enlarged behind the mirror.
Can a convex lens form a virtual image?
Yes. With the object between the optical centre and focus, a convex lens forms a virtual, erect and enlarged image on the object’s side.
How do I interpret magnification?
Positive magnification indicates an erect image; negative magnification indicates an inverted image. A magnitude greater than one means enlargement, while a magnitude less than one means diminution.
Why must focal length be in metres for lens power?
A dioptre is one reciprocal metre. Converting focal length into metres ensures that P = 1/f gives power in dioptres.
Does a higher refractive index mean light travels faster?
No. Since n = c/s, a higher absolute refractive index corresponds to a lower light speed in the medium.
Can a virtual image be seen even though it cannot be projected on a screen?
Yes. Your eyes receive rays that appear to originate from the virtual image position. A plane-mirror image is a familiar example.
Where can I revise Light Reflection and Refraction notes?
Visit our Light Reflection and Refraction Class 10 notes and mind map , then practise the worksheet to check your understanding.
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