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Light & Optics — Homi Bhabha Class 9 Physics MCQs with Solutions
Free Homi Bhabha Class 9 Physics Light & Optics MCQs with step-by-step solutions covering Reflection & Refraction, Spherical Mirrors, Lenses, Shadow Formation, Dispersion through a Prism, Optical Instruments. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Reflection & Refraction · easy · theory
The angle of incidence of a ray of light striking a surface is measured between the incident ray and which line?
A. The horizontal ground
B. The reflecting surface
C. The normal drawn at the point of incidence ✓ Correct
D. The reflected ray
Solution: By definition, the angle of incidence is the angle between the incident ray and the normal (the perpendicular) drawn at the point where the ray meets the surface, not the surface itself.
Q2 — Spherical Mirrors · easy · theory
For a spherical mirror, the focal length f is related to its radius of curvature R by which relation?
A. f = R
B. f = R/4
C. f = R/2 ✓ Correct
D. f = 2R
Solution: The focus of a spherical mirror lies midway between the pole and the centre of curvature, so the focal length is half the radius of curvature: f = R/2.
Q3 — Lenses · easy · theory
A convex lens is also known as a:
A. Cylindrical lens
B. Diverging lens
C. Plane lens
D. Converging lens ✓ Correct
Solution: A convex lens is thicker in the middle and brings parallel rays together at a focus, so it is called a converging lens. A concave lens spreads rays out and is the diverging lens.
Q4 — Shadow Formation · easy · theory
Shadows are formed mainly because light travels:
A. In curved paths around objects
B. Only during the daytime
C. Faster through opaque objects
D. In straight lines ✓ Correct
Solution: Light travels in straight lines (rectilinear propagation). When an opaque object blocks these straight rays, the region behind it receives no light and a shadow forms.
Q5 — Dispersion through a Prism · easy · theory
When white light passes through a glass prism and splits into its component colours, this phenomenon is called:
A. Dispersion ✓ Correct
B. Reflection
C. Refraction
D. Diffraction
Solution: The splitting of white light into its seven constituent colours (VIBGYOR) as it passes through a prism is called dispersion, which happens because different colours bend by different amounts.
Q6 — Optical Instruments · easy · theory
Which optical instrument is used to see distant heavenly bodies such as stars and planets?
A. A kaleidoscope
B. A periscope
C. A telescope ✓ Correct
D. A microscope
Solution: A telescope is designed to view distant objects like stars and planets. A microscope is used for tiny, nearby objects, and a periscope is used to see over or around obstacles.
Q7 — Reflection & Refraction · hard · numerical
A ray of light strikes a plane mirror making an angle of 30° with the mirror surface. The angle of reflection (measured from the normal) is:
A. 120°
B. 30°
C. 90°
D. 60° ✓ Correct
Solution: The angle of incidence from the normal $= 90° - 30° = 60°$, so the angle of reflection is also 60°.
Q8 — Reflection & Refraction · hard · theory
The speed of light is greatest in:
A. diamond
B. vacuum ✓ Correct
C. glass
D. water
Solution: Light travels fastest in vacuum; denser media (water, glass, diamond) slow it down.
Q9 — Spherical Mirrors · hard · numerical
A concave mirror has a focal length of 15 cm. Its radius of curvature is:
A. 7.5 cm
B. 30 cm ✓ Correct
C. 45 cm
D. 15 cm
Solution: Radius of curvature $R = 2f = 2 \times 15 = 30$ cm.
Q10 — Spherical Mirrors · hard · theory
When an object is placed beyond the centre of curvature of a concave mirror, the image formed is:
A. real, inverted and diminished ✓ Correct
B. virtual and diminished
C. real, erect and magnified
D. virtual, erect and magnified
Solution: For an object beyond C, a concave mirror forms a real, inverted, diminished image between F and C.
Q11 — Lenses · hard · numerical
The power of a lens of focal length 25 cm is:
A. +4 D ✓ Correct
B. +2.5 D
C. +0.25 D
D. +25 D
Solution: $f = 25$ cm $= 0.25$ m, so power $= \dfrac{1}{0.25} = +4$ D.
Q12 — Lenses · hard · theory
A concave lens always forms an image that is:
A. real, inverted and magnified
B. virtual, erect and diminished ✓ Correct
C. real and erect
D. virtual and magnified
Solution: For all object positions, a concave (diverging) lens forms a virtual, erect, diminished image.
Q13 — Shadow Formation · hard · theory
The dark central region of a shadow, where light is completely blocked, is called the:
A. umbra ✓ Correct
B. focus
C. aperture
D. penumbra
Solution: The umbra is the fully dark part; the lighter surrounding region is the penumbra.
Q14 — Shadow Formation · hard · theory
A shadow is formed only by an object that is:
A. opaque ✓ Correct
B. translucent
C. transparent
D. luminous
Solution: Opaque objects block light and cast shadows; transparent objects let light pass through.
Q15 — Dispersion through a Prism · hard · theory
When white light is dispersed by a prism, the colour that bends the least is:
A. blue
B. violet
C. green
D. red ✓ Correct
Solution: Red light has the longest wavelength and is deviated least; violet is deviated most.
Q16 — Dispersion through a Prism · hard · theory
Different colours of light are dispersed by a prism because in glass they travel at:
A. infinite speed
B. different speeds and so bend by different amounts ✓ Correct
C. the speed of sound
D. the same speed
Solution: Each colour has a slightly different speed (and refractive index) in glass, so each bends by a different amount.
Q17 — Optical Instruments · hard · theory
A periscope, used in submarines to see above the water, works using:
A. a concave mirror only
B. two plane mirrors (or prisms) inclined at 45° ✓ Correct
C. a prism that disperses light
D. a single convex lens
Solution: Two parallel mirrors at 45° reflect light down the tube, letting the viewer see over obstacles.
Q18 — Optical Instruments · hard · theory
The image formed on the film/sensor of a camera is:
A. virtual and diminished
B. real, erect and magnified
C. virtual, erect and magnified
D. real, inverted and diminished ✓ Correct
Solution: A camera's convex lens forms a real, inverted, diminished image of a distant object on the film/sensor.
Q19 — Reflection & Refraction · hard · numerical
The refractive index of a glass block is 1.5 and the speed of light in vacuum is 3 x 10 to the power 8 m/s. What is the speed of light inside the glass?
A. 2.5 x 10 to the power 8 m/s
B. 2 x 10 to the power 8 m/s ✓ Correct
C. 1.5 x 10 to the power 8 m/s
D. 4.5 x 10 to the power 8 m/s
Solution: Refractive index n = c/v, so v = c/n = (3 x 10 to the power 8) / 1.5 = 2 x 10 to the power 8 m/s. Choosing 4.5 x 10 to the power 8 wrongly multiplies instead of divides.
Q20 — Spherical Mirrors · hard · theory
An object is placed exactly at the centre of curvature of a concave mirror. The image formed is:
A. Virtual, erect and magnified
B. Real, inverted and the same size, located at the centre of curvature ✓ Correct
C. Real, inverted and diminished, located beyond C
D. Virtual, erect and diminished
Solution: When an object sits at the centre of curvature C of a concave mirror, the rays return to form a real, inverted image of the same size, also at C. This is the special same-size case used in ray-diagram rules.
Q21 — Spherical Mirrors · hard · numerical
An object is placed 30 cm in front of a concave mirror whose focal length is 15 cm. Using the mirror formula, where is the image formed?
A. 10 cm in front of the mirror
B. 60 cm in front of the mirror
C. 30 cm in front of the mirror ✓ Correct
D. 15 cm behind the mirror
Solution: The object is at 2f (30 = 2 x 15), so the image also forms at 2f. Using 1/v + 1/u = 1/f with u = -30 and f = -15 gives 1/v = -1/15 + 1/30 = -1/30, so v = -30 cm, i.e. 30 cm in front of the mirror, real and inverted.
Q22 — Lenses · hard · theory
An object is placed at 2F (twice the focal length) in front of a convex lens. The image formed is:
A. Real, inverted and the same size, at 2F on the other side ✓ Correct
B. Virtual, erect and magnified
C. Real, inverted and highly diminished
D. A single point image right at the focus
Solution: For a convex lens, an object at 2F gives a real, inverted image of the same size located at 2F on the far side. This mirrors the same-size rule and is the boundary between magnified and diminished images.
Q23 — Shadow Formation · hard · numerical
At a certain time, a 2 m tall pole casts a 3 m long shadow. At the same moment, a nearby tree casts a 12 m long shadow. What is the height of the tree?
A. 8 m ✓ Correct
B. 18 m
C. 12 m
D. 6 m
Solution: Because the sun rays are parallel, the ratio of height to shadow length is the same for both objects: 2/3 = h/12, so h = (2 x 12)/3 = 8 m.
Q24 — Dispersion through a Prism · hard · theory
When white light passes through a prism, red light is deviated the least and violet the most. Which statement best explains why red deviates the least?
A. All colours travel at the same speed inside the glass
B. Red travels slower than violet inside the prism
C. Violet has a longer wavelength than red
D. Red has a longer wavelength and a smaller refractive index in glass, so it bends the least ✓ Correct
Solution: The amount a colour bends depends on the refractive index of the glass for that colour. Red has the longest wavelength and the smallest refractive index, so it slows least and deviates least. Red actually travels faster (not slower) than violet inside glass.
Q25 — Optical Instruments · hard · theory
In a compound microscope, both lenses are convex. The objective lens first forms which kind of image, that the eyepiece then further enlarges?
A. A real, inverted and magnified image ✓ Correct
B. A diminished real image at its focus
C. No image at all
D. A virtual, erect image
Solution: The objective forms a real, inverted, magnified image of the object. The eyepiece then acts like a simple microscope, treating this image as its object and magnifying it further into a large virtual image seen by the eye.
Q26 — Reflection & Refraction · medium · theory
According to the laws of reflection, the angle of incidence is:
A. less than the angle of reflection
B. greater than the angle of reflection
C. equal to the angle of reflection ✓ Correct
D. always 90°
Solution: The angle of incidence equals the angle of reflection, both measured from the normal.
Q27 — Reflection & Refraction · medium · theory
When light travels from air into a denser medium such as glass, it bends:
A. away from the normal
B. along the surface
C. back into air
D. towards the normal ✓ Correct
Solution: On entering a denser medium light slows down and bends towards the normal (refraction).
Q28 — Reflection & Refraction · medium · theory
A pencil placed in a glass of water appears bent at the water surface because of:
A. dispersion of light
B. absorption of light
C. refraction of light ✓ Correct
D. reflection of light
Solution: Light from the submerged part bends as it leaves the water, making the pencil appear bent.
Q29 — Spherical Mirrors · medium · theory
A concave mirror is used as a shaving/make-up mirror because, when the face is close to it, it forms an image that is:
A. real and inverted
B. erect and magnified ✓ Correct
C. inverted and diminished
D. the same size
Solution: For an object within its focus, a concave mirror gives an erect, magnified (virtual) image.
Q30 — Spherical Mirrors · medium · theory
A convex mirror is preferred as a rear-view mirror in vehicles because it:
A. gives an inverted image
B. shows a narrow field of view
C. gives a magnified image
D. gives an erect, diminished image and a wider field of view ✓ Correct
Solution: A convex mirror always forms an erect, smaller image and covers a wider area behind the vehicle.