Definitions - Wave properties

Question 1

Define longitudinal waves and give an example

Answer 1

1. Longitudinal waves are when the displacement is parallel to the direction of the wave
2. Sound waves, seismic p waves

Question 2

Define transverse waves and give an example

Answer 2

1. Transverse waves are when the displacement is at right angles to the direction of the wave
2. Vibrations in strings, ripples in water surfaces, EM waves (microwave)

Question 3

What is a mechanical wave?

Answer 3

1. A wave that needs matter (particles) to transfer energy

2. Waves on a slinky, sound waves, Transverse (s) and longitudinal (p) seismic waves, water waves

Question 4

What is the difference between a displacement-time and displacement-distance graph?

Answer 4

1. In a displacement-time graph, the x axis measures time, so any 2 corresponding points on the graph = T (time period) used to find frequency (f=1/T)
2. In a displacement-distance graph, the x axis measures distance, so the distance between any 2 corresponding points=wavelength (λ)

Question 5

Define displacement

Answer 5

Distance in a direction (can be + or -)

Question 6

Define amplitude

Answer 6

Maximum displacement (m is base unit)

Question 7

Define frequency

Answer 7

How many waves pass by every second (Hz)

Question 8

Define time period

Answer 8

The time between 2 corresponding points on the wave (seconds)

Question 9

Define wavelength

Answer 9

The distance between 2 corresponding points on the wave (metres)

Question 10

Explain diffraction

Answer 10

Diffraction is when waves spread out from the edge of a gap

1. Size of gap similar to λ = more diffraction
2. λ increased (frequency decreased) = more diffraction

Question 11

Explain interference

Answer 11

When 2 or more waves interact/superimpose with one another to form a resultant wave of greater or lower amplitude (pattern).

Question 12

What is constructive interference?

Answer 12

When 2 or more similar waves add up, to create a wave with a bigger amplitude

Question 13

What is destructive interference?

Answer 13

When 2 or more different waves add up to cancel each other out

(Different points of the wave add together, equal frequency but opposite phase, +ve displacement coincides with the -ve displacement of the other)

Question 14

What are the conditions needed for an interference pattern?

Answer 14

1. Sources of the waves must be coherent (emit identical waves with a constant phase difference)
2. Waves must be monochromatic (of a single λ/light)

Question 15

What are the two properties of an EM wave?

Answer 15

1. Electric field
2. Magnetic field

EM wave created by moving electrons through electrical/magnetic means by giving them heat energy, x rays or radioactive decay.

Moving electrons move back and forth to produce oscillating electric and magnetic fields (travel at c)

Question 16

What properties of a wave does resonance affect?

Answer 16

Affects wave amplitude

Question 17

How would you use reflection to get an inverted image?

Answer 17

Concave lens

Question 18

How would you use reflection to get a smaller and upright image?

Answer 18

Convex Lens

Question 19

How does simple harmonic motion link in with waves?

Answer 19

Periodic motion can be mapped on a graph

Question 20

When would the Doppler shift of a source result in a wave with a longer wavelength?

Answer 20

You’re moving away from source

Or the distance between you and the source is expanding

Question 21

What is refraction?

Answer 21

1. Light wave changes speed and direction

2. Goes from one medium into another

Question 22

Why is the image called a virtual image and not a real image?

Answer 22

1. It cannot be cast onto a screen

2. The image in a plane mirror is the same size and same way up as the object