P6 Transverse and Longitudinal Waves (page 218)

Question 1

Waves transfer energy from one place to another without transferring what?

Answer 1

any matter (stuff)

Question 2

What direction do waves transfer energy?

Answer 2

in the direction they are travelling.

Question 3

When waves travel through a medium, what happens to the particles of the medium?

Answer 3

they oscillate and transfer energy between each other (see page 167). But overall the particles stay in the same place - only energy is transferred.

Question 4

If you drop a twig into a calm pool of water, what happens?

Answer 4

ripples form on the water’s surface.

Question 5

Do the ripples carry the water (or the twig) away from with them?

Answer 5

No

Question 6

If you strum a guitar string and create soundwaves,do the soundwaves carry the air away from the guitar and create a vacuum?

Answer 6

No

Question 7

What is meant by the amplitude of a wave?

Answer 7

it is the maximum displacement of a point on the wave from its undisturbed position.

Question 8

Explain what the wavelength is?

Answer 8

it is the distance between the same point on two adjacent waves (e.g. between the rough of one wave and the trough of the wave next to it.

(see diagram 1 on page 218).

Question 9

Explain what ‘frequency’ is regarding waves?

Answer 9

the frequency is the number of complete waves passing a certain point per second.

Question 10

How is Frequency measured?

Answer 10

in hertz (Hz). 1 Hz is 1 wave per second.

Question 11

From the frequency, you can find the period of a wave using what equation?

Answer 11

Period (s) T = 1
___
f - Frequency (Hz)

see diagram 2 on page 218.

(this is the amount of time it takes for a full cycle of the wave).

Question 12

All waves are either what?

Answer 12

Transverse or Longitudinal.

Question 13

What is Transverse Waves?

Answer 13

the oscillations (vibrations) are perpendicular (at 90°) to the direction of energy transfer.

(transverse waves have sideways vibrations). see diagram 3 on page 218).

Question 14

Are most waves transverse?

Answer 14

Yes.

Question 15

Give examples of transverse waves?

Answer 15

All electromagnetic waves, e.g. light (p.220)
Ripples and waes in water (p.219)
A wave on a string.

Question 16

What is Longitudinal Waves?

Answer 16

the oscillations are parallel to the direction of energy transfer.

(longitudinal waves have parallel vibrations).

Question 17

Give an example of sound waves in air?

Answer 17

e.g. If you push the end of a spring you get a longitudinal wave. Vibrations in the same direction as wave travels.

(see diagram 4 on page 219).

Question 18

Give some examples of mechanical waves?

Answer 18

Water waves
shock waves
waves in springs and ropes

are all examples of mechanical waves.

Question 19

What is means by ‘the wave speed’?

Answer 19

the speed at which energy is being transferred (or the speed the wave is moving at).

Question 20

What is the Wave equation (this applies to all waves?

Answer 20

V = fλ

v - Wave speed (m/s)
f - frequency (Hz)
λ - wavelength (m)

see diagram equation on page 218

Question 21

A radio wave has a frequency of 12.0 x 10⁶ Hz.

Find its wavelength. (the speed of radio waves in air is 3.0 x 10⁸ m/s)

Answer 21

λ = v ÷ f

=  (3.0 x 10⁸) ÷ (12.0 x 10⁶) = 25 m

Question 22

A wave has a speed of 0.15 m/s and a wavelength of 7.5 cm. Calculate its frequency (4 marks)

Answer 22

7.5 ÷ 100 = 0.075 m (1 mark)

wave speed = frequency x wavelength, so frequency = wave speed ÷ wavelength (1 mark)
= 0.15 ÷ 0.075 (1 mark)
= 2 Hz (1 mark)