Progressive Waves

Question 1

What is a progressive wave?

Answer 1

An oscillation that travels through matter (or in some cases a vacuum) transferring energy from one place to another but not transferring any matter

Question 2

How do transverse waves travel?

Answer 2

They travel in oscillations at 90° to the direction of energy transfer

Question 3

Examples of transverse waves

Answer 3

Surface water waves, S waves, all electromagnetic waves

Question 4

How does a longitudinalwave travel?

Answer 4

Longitude or waves travel in oscillations that vibrate parallel to the direction of energy transfer

Question 5

Examples of longitude waves

Answer 5

Sound waves, p-waves

Question 6

Features of a transverse wave

Answer 6

Mechanical waves - they can travel through solids but not liquid liquids

EM waves - they can travel through solid liquids and gases

They can be polarised

Question 7

Features of longitude and waves

Answer 7

They can travel through solids and liquids

They cannot be polarised

They consist of compression and rarerefraction

Question 8

Definition of displacement (waves)

Answer 8

The distance moved by particles from their usual position

Question 9

Definition of frequency (waves)

Answer 9

The number of wavelengths passing a point per unit time (Hz)

Question 10

Definition of time period or period of oscillation

Answer 10

The time taken for one oscillation or a wave to move one whole wavelength past a given point (seconds)

Question 11

How do you calculate the time period of a wave?

Answer 11

Time period = 1/frequency

Question 12

What is the law of reflection?

Answer 12

The angle that the light hits the surface will be the same as the angle the light is reflected at

Angle of incidence = angle of reflection

Question 13

Describing an experiment to prove the law of reflection

Answer 13

• Shine a ray of light from a light box onto a mirror surface
• Draw the normal against the mirror (a perpendicular line)
• Measure the angle of incidence (the angle between the incoming light ray and the normal)
• Then measure the angle of reflection (the angle between the reflected ray and the normal)
• The law of reflection will be proved if these angles are equal to each other

*repeat multiple times for multiple different angles

Question 14

What is a wavefront?

Answer 14

 a surface made up of all points in a wave that are in faith with each other

Question 15

Similarities between reflection and refraction

Answer 15

• They both involve a wave changing direction at a boundary
• The frequencies stays the same
• Both involve energy transfer

Question 16

Differences between reflection and refraction

Answer 16

• Reflected waves remain in the same medium whereas reflected waves change medium
• The wavelength of reflected waves stays the same whereas the wavelength of refracted waves changes

Question 17

Why does the wavelength of a refracted wave change?

Answer 17

V or c = f λ
Frequency remains constant therefore if the speed changes (when travelling through a different medium) the wavelength must also change to maintain equality

V is directly proportional to λ
Meaning if one increases the other also increases

Question 18

What happens to the frequency and wavelength when a wave reflects off a surface?

Answer 18

The speed changes, however the wavelength and frequency stay the same

Question 19

What is a concave mirror used for?

Answer 19

Concave mirrors reflect light inward to one focal light therefore they are mostly used to focus light

Question 20

Definition of refraction

Answer 20

When waves change direction and speed when passing from one medium to another - the change in density changes the speed

Question 21

How does light refract when travelling from air to glass?

Answer 21

It enters a denser medium, therefore it slows down

This means that the light bends towards the normal

Question 22

How does life react when travelling from glass to air?

Answer 22

It enters a less dense medium meaning it speeds up

This means that the light will bend away from the normal

Question 23

Where do you draw the normal?

Answer 23

90° to the surface it is perpendicular

Question 24

What equation do you use to find the refractive index?

Answer 24

n = c/v

Refractive index = speed of light in a vacuum / velocity of light in a substance

Question 25

What is the refractive index?

Answer 25

A measure of how much the speed of the wave has changed

Question 26

Five properties of electromagnetic waves

Answer 26

- transverse waves - oscillate perpendicular to the direction of travel - can travel through a vacuum - do not need a medium - transfer energy - exhibit wave particle duality

Question 27

EM waves in order of longest to shortest

Answer 27

Radio waves, microwaves, infrared, visible, UV, x-rays, gamma rays

Question 28

EM waves in order of highest to lowest frequency

Answer 28

Gamma rays, x-rays, UV, visible, infrared, microwave, radio waves

Question 29

Equation for intensity

Answer 29

I = P/A Intensity = power / area Measured in W/m²

Question 30

What is intensity measured in?

Answer 30

W/m²

Question 31

Definition of intensity

Answer 31

Power per unit area

Question 32

What is the relationship between wave intensity and amplitude?

Answer 32

Intensity ∝ amplitude ² This means if amplitude increases by a factor of 3, intensity increases by a factor of 9 (3²)

Question 33

Define diffraction

Answer 33

The spreading of a wave when it passes through a gap or moves around an obstacle It is wave behaviour as particles cannot bend around a barrier but waves can

Question 34

What is refraction?

Answer 34

The change of direction of a wave as it moves through a different medium/density it changes speed

Question 35

If a wave travels into dense medium. How does the refractive index change?

Answer 35

It increases as the wave gets slower

Question 36

If a wave travels into a less dense medium, how does the refractive index change?

Answer 36

It decreases as the wave gets faster

Question 37

Refractive index of air

Answer 37

1.00

Question 38

Refractive index of water

Answer 38

1.3

Question 39

Refractive index of glass

Answer 39

1.50

Question 40

Snell’s law

Answer 40

Sin c = 1/n nsinθ = constant

Question 41

What equation do you not get given for refraction?

Answer 41

n1sinθ1 = n2sinθ2 n1 - refractive index of material 1 n2 - refractive index of material 2 θ1 - angle of incidence θ2 - angle of refraction

Question 42

How would you plot a graph after measuring the angle of incident and the angle of refraction?

Answer 42

sin(i) / sin(r) = normal normal = gradient sin(i) - y-axis sin(r) - x-axis

Question 43

Experiment to calculate the refractive index of a transparent semi-circular block

Answer 43

1. On a plain piece of paper draw around a protractor marking the perpendicular line through the centre 2. Place the semi-circular block on top of the markings with the centre of the aligned with the 0° on the protractor. 3. Set up the light box at an angle. 4. Using a pencil and ruler trace the right entering the block and leaving it. 5. Repeat this moving the right around every 10° up to 80° 6. Calculate each angle of incidence and each angle of refraction against the normal 7. Plot a graph of sinθ1/sinθ2 -The gradient or equal to refractive index m=n Systematic errors - the lines should be traced from the centre of the light each time Random errors - use a pencil with a sharp tip, use a concentrate laser to produce a more defined race so there’s less uncertainty when tracing the lines as a light box may be blurry, repeat experiment and find an average reading of each angle of refraction