Light

Question 1

What is a luminous object?

Answer 1

Objects such as the sun, electric lamps and candles which make their own light.

Question 2

What are non luminous objects?

Answer 2

Objects that do not make their own light but reflect it from a luminous source.

Question 3

How does light travel and how do we see it?

Answer 3

Light travels in straight lines. The beams are visible because dust particles in the air reflect light into our eyes.

Question 4

What is a beam? And what is a ray?

Answer 4

Beam: A stream of light and is shown by a number of rays.

Ray: the direction of the path in which light is travelling.

Question 5

What are the types of beams?

Answer 5

Beams may either be parallel, diverging (spreading out) or converging (getting narrower)

Question 6

How are shadows formed?

Answer 6

Because some objects which are said to be opaque do not allow light to pass through them. And because light travels in straight lines.

Question 7

What is opaque?

Answer 7

not able to be seen through; not transparent.

Question 8

What is transparent?

Answer 8

allowing light to pass through so that objects behind can be distinctly seen.

Question 9

What is translucent?

Answer 9

allowing light, but not detailed shapes, to pass through; semi-transparent.

Question 10

What is umbra?

Answer 10

the fully shaded inner region of a shadow cast by an opaque object, especially the area on the earth or moon experiencing the total phase of an eclipse.

Question 11

What is penumbra?

Answer 11

the partially shaded outer region of the shadow cast by an opaque object.

Question 12

Give an example for how light travels faster than sound?

Answer 12

A thunderstorm. The flash of lightning is seen before the thunder is heard.

Question 13

What is the law of reflection?

Answer 13

The angle of incidence equals the angle of reflection.

Question 14

Where is the normal of an angle found?

Answer 14

The perpendicular to the mirror at the point where the incident ray strikes

Question 15

Where is the angle of incidence found?

Answer 15

Between the incident ray and the normal

Question 16

Where is the angle of reflection found?

Answer 16

Between the reflected ray and the normal

Question 17

What happens when a parallel beam of light falls on a plane mirror?

Answer 17

It is reflected as a parallel beam and a regular reflection occurs.

Question 18

What happens when a parallel beam of light falls on a rough surface?

Answer 18

The light is reflected irregularly and the rays in an incident parallel beam are reflected in many directions.

Question 19

What is a real image?

Answer 19

One which can be produced on a screen (as in a pinhole camera) and is formed by rays that actually pass through it.

Question 20

What is a virtual image?

Answer 20

A virtual image cannot be formed on a screen and is produced by rays which seem to come from it but do not pass through it.

Question 21

How does a kaleidoscope work?

Answer 21

A kaleidoscope works by reflecting light. Light travels in a straight line. When light bumps into something it changes direction. If light bumps into something shiny it reflects back in the direction it came from. In a kaleidoscope the two mirrors are usually kept at the same angle about 60 degrees and different designs are made by hundreds of tiny coloured beads which can be moved around between the mirrors.

Question 22

What is refraction?

Answer 22

The bending of light when it passes from one material (called a medium) to another is called refraction.

Question 23

What happens when a ray of light enters an optically denser medium at an angle ? (Air to glass)

Answer 23

The ray of light is bent towards the normal ie the angle of refraction is less than the angle of incidence.

Question 24

What happens when a ray of light is bent away from the normal?

Answer 24

When it enters an optically less dense medium. (Glass to air)

Question 25

What happens to a ray emerging from a parallel sided block?

Answer 25

A ray emerging from a parallel sided block is parallel to the ray entering but is displaced sideways.

Question 26

What happens to a ray revelling along the normal?

Answer 26

A ray travelling along the normal is not refracted.