Block 3: Physics of waves

Question 1

What is the law of reflection?

Answer 1

angle of reflection=angle of incidence

Question 2

How does a plane mirror form an image?

Answer 2

Light rays from an image are reflected by the mirror so they change direction and go back into our eyes. But we think that light travels in a straight line and so the image appears to be behind the mirror.

Question 3

Define refraction:

Answer 3

The change of speed or direction of a light ray when it crosses a boundary into a new medium.

Question 4

What is the refracted index of a material?

Answer 4

The quantity that describes how much light is slowed down when passing from one medium to another.
speed of light in a vacuum/speed of light in a material

Question 5

Snell’s law:

Answer 5

n1.sini = n2.sinr
OR
n= sini/sinr

Question 6

What is a critical angle?

Answer 6

An angle that the incident ray makes when reflected ray makes 90 degrees before ray can no longer escape the medium.

Question 7

Total internal reflection:

Answer 7

happens if light strikes a boundary beyond which medium has a lower index of refraction and when the angle of incidence is greater than the critical angle.

Question 8

How are the critical angle and refractive index related?

Answer 8

The critical angle depends on the material through which it is travelling.
Greater refractive index means smaller critical angle.

Question 9

How is total internal reflection used?

Answer 9

In fibre optics which allows for quicker communication signals
used to probe internal organs without surgery

Question 10

What is the difference between a converging lens and a diverging lens?

Answer 10

A converging lens is fatter in the middle than on the edges while a diverging lens is thinner in the middle than on the edges.

Question 11

How does a magnifying glass produce an image?

Answer 11

It’s a converging lens that shows an image closer to the lens than the principals focus. The rays don’t cross each other before the eye so the image created is virtual.

Question 12

How do we use waves in physics?

Answer 12

As a model to explain the behaviour of light and sound.

Question 13

What is a transverse wave?

Answer 13

Is where the particles carrying the wave from side to side, at right angles to the direction in which the wave is moving.

Question 14

What is a longitudinal wave?

Answer 14

It’s where the particles carrying the wave move back and forth, along the direction in which the wave is moving.

Question 15

Define wavelength:

Answer 15

the distance between two adjacent points.

Question 16

What is the frequency of a wave?

Answer 16

the number of cycles completed in one minute.

Question 17

what is the speed of a wave?

Answer 17

the product of frequency and wavelength of a wave.

Question 18

What is a wave cycle?

Answer 18

the pattern that the wave repeats.

Question 19

Define amplitude:

Answer 19

maximum displacement of equilibrium.

Question 20

What happens to the frequency of a wave when it changes medium?

Answer 20

It stays the same.

Question 21

Define diffraction:

Answer 21

the ability that waves have to bend around obstacles.

Question 22

What must the width of the gap of a barrier be if you want to produce the greatest diffraction effect?

Answer 22

For the greatest diffraction effect, the width of the gap should be equal to the wavelength of the waves.

Question 23

When does a wave reflect?

Answer 23

When it bounces off of the boundary between two materials.

Question 24

When does a wave refract?

Answer 24

When it’s speed changes.

Question 25

How is white light dispersed by a prism?

Answer 25

A prism disperses white light into it’s component colours, but since the refractive index for any medium varies slightly with wavelength some colours of light are more strongly refracted than others because their speed decreases more.

Question 26

What is the electromagnetic spectrum?

Answer 26

the entire distribution of electromagnetic radiation according to frequency or wavelength.

Question 27

What are the different sections of the electromagnetic spectrum?

Answer 27

increasing frequency and decreasing wavelength:

radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gramma rays.

Question 28

What is the source of electromagnetic waves?

Answer 28

an accelerating charge

Question 29

What are some uses of electromagnetic waves?

Answer 29

Radio waves broadcast tv and radio channels
infrared waves are used for heat sensing
UV rays are used in sun beds
X-rays are used in medicine to see bone structure
gramma rays are used to sterilize medical equipment

Question 30

What is the speed of light?

Answer 30

300 000 000 m/s