Ray Model of Light

Question 1

What is a ray?

Answer 1

The path along which light energy travels.

Question 2

What is a beam of light?

Answer 2

A bundle of light rays.

Question 3

What are the characteristics of images formed by plane mirrors?

Answer 3

Same size as object, upright, laterally inverted, virtual, image distance from mirror=object distance from mirror.

Question 4

What is an incident ray?

Answer 4

The angle of light approaching a reflecting surface.

Question 5

What is the point of incidence?

Answer 5

The point where the incident ray meets the reflecting surface.

Question 6

What is the reflected ray?

Answer 6

The ray of light bouncing off the reflecting surface.

Question 7

What is the normal?

Answer 7

The ling perpendicular to the reflecting surface and passing through the point of incidence.

Question 8

What is the angle of incidence?

Answer 8

The angle between the incident ray and the normal, usually represented by i.

Question 9

What is the angle of reflection?

Answer 9

THe angle between the reflected ray and the normal, usually represented by r.

Question 10

What are the laws of reflection?

Answer 10

1. Angle of incidence = angle of reflection
2. Incident ray, reflected ray and normal all lie on the same plane.

Question 11

Name uses of plane mirrors.

Answer 11

• interior design: on a wall, makes a room look bigger
• optical testing
• checking one’s appearance

Question 12

Characteristics of images formed by convex mirror?

Answer 12

Images are upright and diminished. Allows a wider field of vision.

Question 13

Name uses of convex mirrors.

Answer 13

• security mirror in shop: allows staff to observe a large area of shop
• mirrors at blind corners of roads

Question 14

Characteristics of images formed by concave mirrors?

Answer 14

Object near —> upright+magnified
object further away —> inverted

Question 15

Name uses of concave mirrors.

Answer 15

• dentist’s mirror: magnify image of teeth
• make-up mirror: make a person’s face lok bigger for easier application of makeup

Question 16

How is light reflected on a smooth surface?

Answer 16

A parallel beam of light that falls onto a smooth surface will be reflected as a parallel beam. The normals at all points of incidence are parallel. Hence, all rays have the same incident and reflected angles. A sharp image is produced.

Question 17

How is light reflected on a rough surface?

Answer 17

If a parallel beam of light falls onto a rough surface, it is reflected in many directions as the normals at all points of incidence are not parallel. As the angle of incidence at each point is different, the angle of reflection for every ray will be different. This does not produce a sharp image.

Question 18

What is refraction?

Answer 18

The bending of a light ray as it passes from one medium to another.

Question 19

What causes refraction?

Answer 19

Light travels at different speeds in different optical media.
When the light ray travels from an optically less dense medium into an optically denser medium, it slows down and bends towards the normal.

Question 20

How does misperception of depth occur?

Answer 20

The light rays travelling from water to air refract away from the normal.
However, our brain tends to tell us that light rays travel in a straight line.
The light rays emerging from the water surface appear to diverge from a point above the object.
The observer sees the image of the object at a shallower depth.

Question 21

What is dispersion?

Answer 21

The splitting of white light into its component colours.

Question 22

ow does dispersion occur?

Answer 22

When a beam of white light passes through a glass prism, the light splits up and disperses into a spectrum.

Question 23

What colours travels the fastest and slowest through a prism?

Answer 23

Red travels fastest and bends the least.
Violet travels slowest and bends the most?

Question 24

What are the 7 colours in the spectrum?

Answer 24

Red, orange, yellow, green, blue, indigo, violet.

Question 25

Which two EM radiation may cause internal heating of body tissues?

Answer 25

• Radio waves: radio broadcast
• Microwaves: microwave oven for heating food

Question 26

Purpose and harmful effects of infrared radiation.

Answer 26

Thermal imagine camera to scan people for fever, can cause skin burns.

Question 27

Purpose and harmful effect of UV radiation.

Answer 27

Detect counterfeit bank notes and cheques, causes severe sunburn and damages cells.

Question 28

Which two EM radiation damage cells and cause mutations which may cause cancer and cell death?

Answer 28

• X-rays: medical images of bones
• Gamma rays: kill cancer cells

Question 29

Purpose and harmful effect of visible light

Answer 29

Seeing things around us, causes decolourisation of old photos and paintings.