A line at 90° to the surface at the point where the ray hits it.

A ray hits a mirror at 30° to the surface. What is the angle of incidence?

60° (90° − 30°), as angles are measured from the normal.

Give three properties of an image in a plane mirror.

Virtual, the same size as the object, and laterally inverted (also the same distance behind the mirror).

What is a virtual image?

An image that cannot be projected on to a screen because light does not actually pass through it.

What causes refraction?

A change in the speed of the wave at a boundary.

What happens when light goes from air into glass?

It slows down and bends towards the normal.

What happens when light goes from glass into air?

It speeds up and bends away from the normal.

What is the critical angle?

The angle of incidence at which the angle of refraction is 90°.

When does total internal reflection happen?

When light travels towards a less dense material at an angle of incidence greater than the critical angle.

How does an optical fibre keep light inside?

The light hits the wall at more than the critical angle and is totally internally reflected again and again.

What happens to water waves moving from deep to shallow water?

They slow down, the wavelength decreases and they bend towards the normal; the frequency stays the same.

Give one use of prisms.

Periscopes and binoculars, using total internal reflection.

Reflection and refractionIB MYP Physics: Flashcards

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Question

State the law of reflection.

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State the law of reflection.: The angle of incidence equals the angle of reflection.
What is the normal?: A line at 90° to the surface at the point where the ray hits it.
A ray hits a mirror at 30° to the surface. What is the angle of incidence?: 60° (90° − 30°), as angles are measured from the normal.
Give three properties of an image in a plane mirror.: Virtual, the same size as the object, and laterally inverted (also the same distance behind the mirror).
What is a virtual image?: An image that cannot be projected on to a screen because light does not actually pass through it.
What causes refraction?: A change in the speed of the wave at a boundary.
What happens when light goes from air into glass?: It slows down and bends towards the normal.
What happens when light goes from glass into air?: It speeds up and bends away from the normal.
State the equation for refractive index.: n = sin i ÷ sin r.
What is the critical angle?: The angle of incidence at which the angle of refraction is 90°.
When does total internal reflection happen?: When light travels towards a less dense material at an angle of incidence greater than the critical angle.
How does an optical fibre keep light inside?: The light hits the wall at more than the critical angle and is totally internally reflected again and again.
What happens to water waves moving from deep to shallow water?: They slow down, the wavelength decreases and they bend towards the normal; the frequency stays the same.
Give one use of prisms.: Periscopes and binoculars, using total internal reflection.

Exam questions on Reflection and refraction

A student in Lagos investigates reflection using a ray box and a plane mirror laid flat on a sheet of paper. She draws a line at right angles to the mirror at the point where a ray of light hits it. The ray hits the mirror at 30° to the surface of the mirror. She then places a pencil in front of the mirror and looks at its image.
Describe two properties of the image of the pencil seen in the plane mirror.2 marks
In a physics laboratory in Seoul, a ray of light passes from air into a rectangular glass block. The angle of incidence is 50° and the angle of refraction is 30°.
The student then shines a ray of light into the glass block along the normal. State what happens to the direction and the speed of the ray as it enters the glass.2 marks
A student investigates refraction using a rectangular glass block, a ray box and a protractor. She shines a ray of light into the block from air at different angles of incidence and measures the angle of refraction each time. For angles of incidence of 20°, 40° and 60°, she measures angles of refraction of 13°, 25° and 35°.
Use the readings for an angle of incidence of 60° to calculate the refractive index of the glass.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).