P14 - Light

Question 1

Describe the method for the reflection of light practical.

Answer 1

1. Place the mirror on your sheet of paper and mark it
   with a pencil.
2. Shine the ray of light on the mirror and mark the path the light ray takes.
3. Draw the normal where the light ray meets the mirror.
4. Measure the angle of incidence and the angle of reflection.
5. Repeat at least two more times changing the angle of incidence.

Question 2

What is a real image?

Answer 2

A real image is an image formed by a lens that can be projected on a screen.

Question 3

What is a virtual image?

Answer 3

A virtual image is an image seen in a lens or a mirror, from which light rays appear to come after being refracted by a lens or reflected by a mirror.

Question 4

How is the image in a mirror different to you?

Answer 4

The image produced in a plane mirror is virtual, upright and laterally inverted (back to front but not upside down).

Question 5

What is specular diffusion?

Answer 5

Reflection from a smooth surface is called specular reflection’ as the parallel light rays are reflected in a single direction parallel to each other still.

Question 6

What is diffuse reflection?

Answer 6

Light rays reflected off of a rough surface in different directions is called ‘diffuse reflection’.

Question 7

Why does an image change when you look through water?

Answer 7

The image changes when you look through water because the light enters a different medium - they seem to bend because the medium has a different optical density causing the light to move at a different speed.

Question 8

When you move from deep to shallow water what happens to the velocity, wavelength, frequency and direction of the wave?

Answer 8

Velocity: decreases
Wavelength: decreases
Frequency: does not change
Direction of the wave: moves towards the normal.

Question 9

Describe the method for refraction through a glass block practical.

Answer 9

1.Place the glass block in the middle of the page and draw around it.
2.Shine the light ray at an angle to the surface of the block.
3.Draw the path the ray takes through the air.
4. Remove the block and draw the path the ray takes through the block.
5. Mark two normals where the light enters and leaves the block.
6. Measure the angle of incidence and refraction.

Question 10

What happens to light rays when they move from a less dense medium to a more dense medium?

Answer 10

They move towards the normal line

Question 11

What happens to light rays when they move from a more dense medium to a less dense medium?

Answer 11

They move away from the normal line.

Question 12

How do colour filters work?

Answer 12

Colour filters work by absorbing certain wavelengths and transmitting other
wavelengths.

Question 13

Describe transparent objects.

Answer 13

Transmits all light through the object.

Question 14

Describe translucent objects.

Answer 14

Light is transmitted, but is scattered or
refracted as it does so, due to lots of internal boundaries in the object. e.g. a frosted window.

Question 15

Describe opaque objects.

Answer 15

Light does not pass through. Instead the object either absorbs all light that reaches it, or reflects / scatters it at the surface.

Question 16

What does the colour of opaque objects depend on?

Answer 16

● Chemicals called pigments in the surface of materials determine an item’s colour.
● Colour also depends on the range of the
wavelengths in the incident light.
● The pigments absorb certain wavelengths of light and strongly reflect others.
● White surface has no pigments so it reflects any light.

Question 17

What is a lens?

Answer 17

A lens forms an image by refracting light.

Question 18

What is refraction?

Answer 18

Refraction refers to the change of direction and speed of a wave (light) as it travels between mediums with different densities.

Question 19

What is a convex lens represented by in ray diagrams?

Answer 19

<——->

Question 20

What is a concave lens represented by in ray diagrams?

Answer 20

> ———–<

Question 21

What is the principal focus?

Answer 21

The principal focus, F (focal point), of the lens is the point where the rays appear to focus.

Question 22

What is the focal length?

Answer 22

The focal length refers to the distance between the centre of the lens and principal focus.

Question 23

How does a convex lens work?

Answer 23

A convex lens makes parallel rays converge (focus) towards the centre of the lens.

Question 24

How does a concave lens work?

Answer 24

A concave lens makes parallel rays diverge away (spread out) from the centre of the lens.

Question 25

What is the equation for magnification?

Answer 25

Magnification = image height / object height

Question 26

What is short sightedness?

Answer 26

This is where light is focused in front of the retina causing far away objects to appear blurry.

Question 27

What is long sightedness?

Answer 27

This is where light is focused behind the retina, as a result close objects appear to be blurry.