IGCSE Physics Light topical questions

A ray of light strikes a plane mirror.

1. (a)State the law of reflection.[1]
2. (b)The ray hits the mirror at 30° to the mirror surface. Calculate the angle of reflection.[2]
3. (c)Name the line from which both angles are measured.[1]

A student looks at a bright lamp in a plane mirror.

1. (a)State three characteristics of the image formed.[3]
2. (b)Explain why the image is described as virtual.[1]

Light passes through a rectangular glass block.

1. (a)Name the bending effect when light crosses from air into glass.[1]
2. (b)State which way the ray bends as it enters the glass.[1]
3. (c)State which way the ray bends as it leaves the far face back into air.[1]

A torch beam hits a flat mirror at an angle of incidence of 40°. The mirror is then turned so the angle of incidence becomes 55°.

1. (a)State the angle of reflection before the mirror is turned.[1]
2. (b)State the angle of reflection after the mirror is turned.[1]
3. (c)Explain why the angles are measured from the normal rather than from the mirror surface.[2]

A ray of light in air strikes a glass block at an angle of incidence of 45°. The angle of refraction inside the glass is 28°.

1. (a)State the equation linking refractive index with the angles of incidence and refraction.[1]
2. (b)Calculate the refractive index of the glass.[2]
3. (c)Calculate the critical angle for this glass.[2]

A source of light is placed 8.0 cm in front of a plane mirror. A second student suggests the image is 4.0 cm behind the mirror and half the size of the lamp.

1. (a)State whether the student is correct, and give the true position of the image.[2]
2. (b)The lamp is moved to 20 cm from the mirror. State the new image distance.[1]
3. (c)State what happens to the size of the image when the lamp is moved further away.[1]

An object 4.0 cm tall stands 15 cm from a thin converging lens of focal length 10 cm. The image forms on a screen 30 cm on the other side of the lens and is 8.0 cm tall but upside down.

1. (a)Describe the image using all three descriptors.[3]
2. (b)Explain what is meant by a real image.[1]
3. (c)State where the object must be placed for a converging lens to act as a magnifying glass.[1]

An underwater lamp shines light up towards the water–air surface. The refractive index of water is 1.33.

1. (a)Calculate the critical angle for the water–air boundary.[2]
2. (b)One ray from the lamp strikes the surface at 55°. Describe fully what happens to it.[2]
3. (c)A second ray strikes the surface at 30°. Describe what happens to it.[2]

A converging lens has a focal length of 4.0 cm. A 2.0 cm tall arrow stands 12 cm from the lens. A sharp image forms on a screen 6.0 cm behind the lens, and the image measures 1.0 cm tall.

1. (a)Describe the image using all three descriptors.[3]
2. (b)The screen is moved back to 12 cm from the lens. State and explain what is seen on the screen now.[2]
3. (c)State where the arrow would have to be placed for this lens to magnify it.[1]

A right-angled glass prism (refractive index 1.5) is used to turn a light beam through 90°. The beam enters perpendicular to one face and meets the long (hypotenuse) face from inside the glass.

1. (a)Calculate the critical angle of this glass.[2]
2. (b)The beam strikes the hypotenuse face at 45° to its normal. Explain fully what happens to the beam.[3]
3. (c)State one practical use of this prism arrangement.[1]

A person with long sight cannot focus clearly on nearby objects; the eye forms the image behind the retina. A person with short sight cannot focus on distant objects; the image forms in front of the retina.

1. (a)State which lens type corrects long sight and explain how it works.[3]
2. (b)State which lens type corrects short sight and explain how it works.[3]
3. (c)State which condition is corrected with a lens whose principal focus is virtual.[1]

A beam of white light is split by a glass prism into a spectrum on a screen.

1. (a)Name the effect that produces the spectrum.[1]
2. (b)State which colour appears closest to the top of the spectrum (least deviated) and which appears furthest (most deviated).[2]
3. (c)Explain why the colours separate inside the glass.[2]
4. (d)A laser produces monochromatic red light. State what a monochromatic beam would show on the screen instead of a spectrum.[1]