Light

Question 1

Light is propagated by means of …… waves

Answer 1

Transverse waves

Question 2

Define a ray

Answer 2

It is a straight line drawn perpendicularly to the wavefronts with an arrow representing the direction in which lifht is travelling

Question 3

Def a beam

Answer 3

Is a stream of light energy which is represented by a number of rays It may have parallel, diverging or converging rays

Question 4

Def a transparent substance

Answer 4

It is one that transmits light and Through which objects can be clearly seen

Question 5

Def translucent substance

Answer 5

Is one that transmits light but Through which objects cannot be clearly seen

Question 6

Def opaque substance

Answer 6

One which does not transmit light

Question 7

Name 2 kinds of reflection

Answer 7

Diffuse reflection

Regular reflection

Question 8

Def Diffuse reflection

Answer 8

When the reflected light is scattered into various direction due to irregular structure of surface

Question 9

Define Regular reflection

Answer 9

When the reflected light rays are even and in the same direction due to the reflective surface being smooth

Question 10

Name the 2 laws of reflection

Answer 10

The angle of incidence is equal to the angle of reflection

The incident ray, normal and reflected ray all lie in the same plane

Question 11

Name the 6 properties of an image in a plane mirror

Answer 11

Virtual

Erect

Laterally inverted

Same size than object

As far behind the mirror as the object is in front of the mirror

Cannot be projected onto a screen

Question 12

Def a virtual image

Answer 12

It is an image which cannot be projected onto a screen because the rays of light do not pass through the image

Question 13

Draw a periscope using mirrors

Answer 13

Question 14

Draw a periscope using prisms

Answer 14

Question 15

Draw a pinhole camera

Answer 15

Question 16

Name the properties of a pinhole camera

Answer 16

Image is:

Smaller than the object

Real

Inverted Rays of light pass through the image

Question 17

Def refraction

Answer 17

Is the bending of light when it passes obliquely from one medium to another of different optical density

Question 18

Def an optical medium

Answer 18

It is a substance through which light can pass

Question 19

Optical density refers to..

Answer 19

The refracting effect and not to the physical density of the substance

Question 20

Define a Normal

Answer 20

It is a straight line drawn perpendicularly to the refracting surface at the point where light enters or leaves the medium

Question 21

Give the two laws of Refraction

Answer 21

The incident and refracted rays are in the same plane as the normal to the surface at the point of incidence and lie on opposite sides of the normal

For a given colour of light, the ratio of the sine of the angle of incidence to the sine of the angle of refeaction is constant for any two given media

Question 22

Name 4 facts referring to the path of a ray of light through a rectangular glass block

Answer 22

1) . A ray of light is refracted away from the normal when it enters an optically less dense medium obliquely
2) . A ray of light is reflected TOWARDS the normal when it enters an optically denser medium obliquely
3) . A ray of light is not refracted if it enters the medium at right angles
4) . The incidence and refracted ray leaving the block are parallell, but displaced laterally.

Question 23

Name the two reasons why an image appear to be shallower in water than it really is

Answer 23

1. Light is refracted AWAY from the normal when passing from water to air
2. The brain imagines the ray of light to be travelling in a straight line

Question 24

Draw a picture to describe the apparent bending of a pencil in water

Answer 24

Question 25

Show the path of a ray of light through a triangular glass prism

Answer 25

Question 26

Show 5 equations for calculating refractive index

Answer 26

1. n= c/v
2. n= sin i / sin r. From air into denser medium
3. 1/n = sin i / sin r From dense to less dense
4. n = 1/ sin c. c = critical angle
5. n = real depth / apparent depth

Question 27

Define the critical angle

Answer 27

It is the angle of incidence in the medium of greater optical density that results in an angle of refraction of 90^o

Question 28

List and explain the 2 conditions under which total internal reflection occurs

Answer 28

The ray of light must pass from a dense to a less dense optical medium The angle of incidence must exceed the critical angle of the optical medium

Question 29

List some applications where total internal reflections occur

Answer 29

1. Optic fibre cables
2. Endoscopes
3. Periscopes
4. Binoculars

Question 30

Def luminous source

Answer 30

Are objects which emit their own light