Waves

Question 1

Transverse waves

Answer 1

🔹A transverse wave is one where the particles vibrate or oscillate perpendicular to the direction of travel (and energy transfer)

🔹These waves can be polarized.

🔹Examples include: electromagnetic waves like radio waves and visible light.

Question 2

Longitudinal waves

Answer 2

🔹A longitudinal wave is one where the particles vibrate or oscillate parallel to the direction of travel (and energy transfer)

🔹They cannot be polarized

🔹Examples include sound and ultrasound waves.

Question 3

Displacement (x)

Answer 3

Displacement of a wave is the distance from its equilibrium position. It is a vector quantity. It can be positive or negative.

Question 4

Amplitude (A)

Answer 4

Amplitude is the maximum displacement of a particle in the wave from its equilibrium position.

Question 5

Equilibrium position

Answer 5

It is the rest position.

Question 6

Wavelength (λ)

Answer 6

The wavelength of a wave is the distance between any two points on successive oscillations of the wave that are in phase. It is measured in metres.

Question 7

What is a crest and a trough?

Answer 7

A crest is the highest point of a transverse wave and a trough is the lowest point.

Question 8

Period ( T )

Answer 8

The period of a wave is the time taken to produce one complete oscillation or cycle of the wave.

Question 9

Frequency ( f )

Answer 9

The frequency of a wave is the number of complete oscillations per second. It is measured in Hertz (Hz) or s<-1.

Question 10

Phase difference

Answer 10

The phase difference tells us how much a point or a wave is in front or behind another wave.

(Extra bits)
• This can be found from the relative position of the crests or troughs of two different waves of the same frequency.

• Phase difference is measured in fractions of a wavelength, degrees or radians.

Question 11

Waves in anti-phase

Answer 11

When the crest of one wave aligns with the trough of another, they are in antiphase.
(Two waves with a phase difference of 180° or π)

Question 12

Waves in phase

Answer 12

When the crests or troughs are aligned, the waves are in phase.
(Phase difference of 360° or 2π)

Question 13

Progressive waves

Answer 13

Waves that transfer energy are known as progressive waves.

Question 14

Stationary waves

Answer 14

Waves that do not transfer energy are known as stationary waves.

Question 15

What is a time-base setting?

Answer 15

The period of the wave can be determined from the time-base This is how many seconds each division represents, measured commonly in s div-1 or s cm-1

Question 16

Wave equation

Answer 16

🔹The wave equation links frequency, wavelength and speed of a wave.

🔹The wave equation tells us that for a constant speed, the wavelength is indirectly proportional to the frequency.

V = f × λ

Question 17

What is “c” in c=fλ?

Answer 17

It is the wave speed. However, c is often used to represent a specific speed ー the speed of light ( 3 x 10<8 ms<-1).

Question 18

What is wave intensity?

Answer 18

The amount of energy passing through a unit area per unit time is the intensity of the wave.

• Therefore, the intensity is defined as power per unit area.

Question 19

What is intensity proportional to?

Answer 19

The intensity of a progressive wave is directly proportional to its amplitude squared and frequency squared.

• Extra
This means that if the frequency or the amplitude is doubled, the intensity increases by a factor of 4 or 2<2.

Question 20

What is the inverse square law?

Answer 20

Note the intensity is proportional to 1/r<2
• This means when the source is twice as far away, the intensity is 4 times less.
• The 1/r2 relationship is known in physics as the inverse square law.

Question 21

Some examples of transverse waves:

Answer 21

• Water waves
• Electromagnetic waves
• Vibration on a guitar string

Question 22

Some examples of longitudinal waves:

Answer 22

• Sound Waves
• Pushing and Pulling of a slinky
• Ultrasound waves

Question 23

What is the Doppler effect or Doppler shift?

Answer 23

The frequency change due to the relative motion between a source of sound or light and an observer is known as the Doppler effect. (Or doppler shift)

Question 24

What is the wave velocity for sound waves?

Answer 24

340 m/s

Question 25

All electromagnetic waves have the following properties in common:

Answer 25

• They are all transverse waves.
• They can all travel in vacuum.
• They all travel at the same speed in a vacuum - the speed of light (3 × 10<8 m/s).

Question 26

What is the relationship between frequency and energy?

Answer 26

The higher the frequency, the higher the energy of the radiation.

Question 27

Transverse waves can be polarised, this means:

Answer 27

• Vibrations are restricted to one direction.
• These vibrations are still perpendicular to the direction of propagation/energy transfer.

Question 28

Can longitudinal waves be polarized?

Answer 28

They cannot be polarized since they travel parallel to the direction of vibration.

Question 29

What is Wave motion?

Answer 29

Wave motion is when energy is transferred through moving oscillations and vibrations. For example in the vibration of ropes and springs.

Question 30

What is a cathode ray oscilloscope?

Answer 30

It is a laboratory instrument used to display, analyze and measure waveforms of electrical circuits.

Question 31

When is a wave coherent?

Answer 31

When there is a constant phase difference.

Question 32

What is polarization?

Answer 32

When the vibrations are restricted to just one direction and they are still perpendicular to the direction of energy transfer.