4.4 Waves

Question 1

How can you tell electromagnetic waves carry energy?

Answer 1

• things heat up
• ionisation
• loud sounds cause large oscillations in air partials which can make things vibrate
• wave power can be used to generate electricity

Question 2

Define displacement.

Answer 2

How far a point on the wave has moved from its undisturbed - it can be positive or negative.

Question 3

Define amplitude.

Answer 3

Amplitude is the maximum displacement - the distance from a peak to trough to the mean (rest) position.

Question 4

Define wavelength.

Answer 4

The distance between two successive identical points that have the same pattern of oscillation. The distance a wave travels before it repeats itself.

Question 5

Define period.

Answer 5

The time it takes for one complete cycle of oscillation go take place at any point.

Question 6

Define phase difference.

Answer 6

Measured in radians. The amount one wave lags behind the other -the relationship between the pattern of vibration at two points.

Question 7

Define frequency.

Answer 7

The number of oscillations per second passing a given point.

Question 8

Equation for frequency.

Answer 8

Frequency = 1/Time

Question 9

Equation for speed of wave (v).

Answer 9

Speed of wave (v) = frequency (f) x wavelength (y)

Question 10

What is intensity?

Answer 10

A measure of how much energy a wave is carrying

Question 11

Define progressive wave.

Answer 11

A type of wave that travels through a substance or space, carrying energy via the oscillation of particles

Question 12

Define transverse wave.

Answer 12

A type of wave in which oscillations occur at right angles to the direction of wave propagation.

Question 13

Define longitudinal wave.

Answer 13

A type of wave in which oscillations occur parallel to the direct of wave propagation.

Question 14

Define coherence.

Answer 14

Constant phase difference.

Question 15

Why is it difficult to produce coherent light waves?

Answer 15

It is difficult to control the frequency.

Question 16

Equation for fringe spacing?

Answer 16

X=(wavelength x D)/ a (spacing between slits)

Question 17

What is the equation for intensity?

Answer 17

Power/area

Question 18

What’s intensity measured in?

Answer 18

Wm^-2

Question 19

What do all electromagnetic waves have in common?

Answer 19

• speed
• transverse
• can be refracted, reflected, diffracted and can undergo interference
• their progressive waves carry energy
• can be polarised

Question 20

Wavelength of radio waves.

Answer 20

10^-1 to 10^6

Question 21

Wavelength of microwaves.

Answer 21

10^-3 to 10^-1

Question 22

Wavelength of infrared waves.

Answer 22

7x10^-7 to 10^-3

Question 23

Wavelength of visible light.

Answer 23

4x10^-7 to 7x10^-7

Question 24

Wavelength of UV waves.

Answer 24

10^-8 to 4x10^-7

Question 25

Wavelength of X-rays

Answer 25

10^-13 to 10^-8

Question 26

Wavelength of gamma rays.

Answer 26

10^-16 to 10^-10

Question 27

What happens if the second polarising filter is rotated by 45 degrees?

Answer 27

The intensity will be half that getting through the first filter.

Question 28

When do you get the most diffraction?

Answer 28

When the gap is the same size as the wavelength.

Question 29

What does refractive index measure?

Answer 29

How much a material slows down light.

Question 30

What is the absolute refractive index of a material?

Answer 30

The ratio between the speed of light in a vacuum and the speed of light in that material.

Question 31

Equation for refractive index.

Answer 31

N = c/ v

Question 32

What does snells law do?

Answer 32

Uses angles to calculate the refractive index.

Question 33

What is snells law?

Answer 33

N1sinø1 = n2sinø2

Question 34

What happens to the angle of incidence when the angle of refraction is a right angle?

Answer 34

The angle of incidence is critical.

Question 35

What happens to snells law for light hitting a material to air boundary?

Answer 35

Sin c = 1/n

Question 36

What happens to the wavelength when the pip has a closed end?

Answer 36

It is a quarter wavelength.

Question 37

What are progressive waves?

Answer 37

Waves that transfer energy away from a source, via oscillations of particles

Question 38

How many radians is a full cycle of a wave?

Answer 38

2pi

Question 39

Define intensity.

Answer 39

Rate of flow of energy per unit area at right angles to the direction of travel of the wave. Measured in Wm-2.

Question 40

What is the refractive index of air?

Answer 40

1

Question 41

Define interference.

Answer 41

When two waves superimpose at a point there is a change in overall displacement.

Question 42

What is a node?

Answer 42

Occurs where amplitude/displacement is always 0

Question 43

What is an antinode?

Answer 43

Occurred where the amplitude takes the maximum possible value

Question 44

Big equation for intensity

Answer 44

(Energy/time)/area

Question 45

How are intensity and amplitude related?

Answer 45

I=A^2

Question 46

What is a plane polarised wave?

Answer 46

We're all oscillations of the field and the direction of travel are confined to a single plane

Question 47

What is a polarising filter?

Answer 47

Produces plane polarised light by selective absorption of one component of the incident oscillations - only component of light polarised perpendicular to that direction

Question 48

What are differences between standing and progressive waves?

Answer 48

Progressive waves transfer energy, all points on a progressive wave have different phase (in one λ), stationary wave traps energy in pockets, stationary wave has nodes and antinodes

Question 49

What is unique about EM waves?

Answer 49

They travel at c (3*10^*8) in a vacuum

Question 50

When you double the frequency what happens to the speed of a wave, and the speed of oscillation of an individual point on a wave?

Answer 50

The wave speed will not change, the wavelength will just halve proportionally. For an individual point, it will oscillate twice as many times in a second and so it's speed doubles

Question 51

What happens to intensity if amplitude is doubled?

Answer 51

Increased by a factor of 4

Question 52

What happens to intensity and position if separation is halved?

Answer 52

Intensity unchanged | Distance doubles

Question 53

What happens to intensity and position of they become 180 out of phase?

Answer 53

Intensity unchanged | Maxima move to minima

Question 54

Define diffraction

Answer 54

Oaths spreading out after gal or around an obstacle

Question 55

Define intensity

Answer 55

The incident energy per unit area per second

Question 56

What are the conditions necessary to produce visible fringes?

Answer 56

``` Coherent source Constant phase relationship Slits must be close together Similar amplitude Similar intensities ```

Question 57

Define diffraction

Answer 57

Wavefronts spreading after passing through a gap or around an obstacle