Wave Properties

Question 1

What are mechanical waves?

Answer 1

Vibrations which travel through a medium. Eg sound and water waves.

Question 2

What is a transverse wave?

Answer 2

The oscillations of a transverse wave are perpendicular to the direction in which the waves transfer energy. All electromagnetic (included light) waves are transverse.

Question 3

What are longitudinal waves?

Answer 3

The oscillations of a longitudinal wave are parallel to the direction in which the waves transfer energy.
Sound waves are longitudinal.

Question 4

Explain the amplitude of a wave.

Answer 4

The amplitude of a wave is the maximum displacement of a point on the wave from its undisturbed position. The height of the wave crest, or depth of the trough.
The bigger the amplitude of the waves, the more energy the waves carry.

Question 5

What is the wavelength?

Answer 5

the wavelength of a wave is the distance from a point on the adjacent wave.

Question 6

What is the frequency of a wave?

Answer 6

The number of waves passing a fixed point every second is called the frequency. The unit is hertz (Hz).

Question 7

What is the period of a wave?

Answer 7

The period of the wave is the time taken for each wave to pass a fixed point.

Question 8

What is the equation for the period of a wave?

Answer 8

period (seconds) = 1/frequency (Hz)

Question 9

What is the speed of waves?

Answer 9

The speed of the wave is the distance travelled by each wave every second through a medium. Energy is transferred by the waves at this speed.

Question 10

What is the equation for wave speed?

Answer 10

Wave speed, = frequency x wavelength

Question 11

How can you investigate reflection of waves?

Answer 11

Using a ripple tank. If the incident wave is not parallel to the barrier before or after reflection. The reflected wavefront moves away from the barrier at the same angle to the barrier as the incident wavefront.

Question 12

What is wave refraction?

Answer 12

Refraction of waves is the change of the direction in which they are travelling when they cross a boundary between one medium and another medium. eg from deep water to shallow water.

Question 13

What does it mean if a wave is transmitted?

Answer 13

Waves that are not absorbed by the substance they re travelling through are transmitted by it. Eg light is mostly transmitted by ordinary glass, but is almost completely absorbed by darkened glass.

Question 14

Why are sound waves longitudinal?

Answer 14

The ai particles vibrate (or oscillate) along the direction in which the waves transfer energy.
The vibrating object pushes and pulls repeatedly on the air. This sends out vibrations of air in waves of compressions and rarefactions.

Question 15

What happens as the amplitude of a sound wave increases?

Answer 15

As the amplitude of the sound wave increases, the loudness of the sound will increase.

Question 16

Why is the frequency of the human ear limited?

Answer 16

Sound waves entering a solid are converted to vibrations and travel through the solid as vibrations. The conversion of sound waves to vibrations of solid only works over a limited frequency range. So the frequency range of the human ear is limited.

Question 17

What is echo sounding?

Answer 17

Echo sounding uses pulses of high-frequency sound waves to detect objects in deep water and to measure water depth below a ship. The pulses from the transmitter are reflected at the sea bed directly below the ship and detected by a receiver at the same depth as the transmitter. Time and distance and speed can be calculated.

Question 18

What is an echo?

Answer 18

An echo is the reflection of sound waves from a smooth surface.

Question 19

What changes the pitch of a sound?

Answer 19

The pitch of a note increases if the frequency of the sound waves increases.

Question 20

What are ultrasound waves?

Answer 20

Sound waves above the highest frequency that humans can detect are called ultrasound waves.

Question 21

What are ultrasound waves used for?

Answer 21

Prenatal scans of a baby in the womb.
To get an image of organs in the body such as the kidney, or damaged ligaments and muscles.
Detecting flaws in metal casting.

Question 22

Explain what each ultrasound wave pulse from the transducer does.

Answer 22

Each ultrasound wave pulse from the transducer:

• is partially reflected from the different tissue boundaries in its path.
• returns to the transducer as a sequence of ultrasound waves reflected by the tissue boundaries, arriving back at different times.

Question 23

Why are ultrasound waves better than x-rays?

Answer 23

• they are reflected at boundaries between different types of tissue, so they can be used to scan organs and other soft tissues in the body.
• non-ionising. Non-ionising radiation is radiation that does not have enough energy to remove an electron to ionise an atom or molecule. So it is harmless when used for scanning.

Question 24

How do ultrasound waves detect metal flaws?

Answer 24

A flaw might be an internal crack, which creates a boundary inside the metal. The ultrasound waves are partly reflected from this boundary.

Question 25

How can you calculate distance travelled by the wave (ultrasound)?

Answer 25

distance travelled by the wave = speed of the ultrasound waves in the body tissue x time taken

Question 26

How can you calculate the depth of the boundary below the surface (ultrasound waves)?

Answer 26

The depth of the boundary below the surface = 0.5 x speed of the ultrasound waves x time taken

Question 27

What are seismic waves?

Answer 27

The energy transferred from earth quakes makes shock waves called seismic waves that travel through the Earth and across its surface.

Question 28

where do earthquakes happen?

Answer 28

Inside the Earth’s crust. The point where an earthquake originates from is called its focus. The nearest point on the surface to the focus is called the epicentre of the earthquake. Earthquakes are recorded by detectors on the surface of the Earth called seismometers.

Question 29

What are primary waves (P-waves)?

Answer 29

Causes the initial tremor lasting about one minute. These are longitudinal waves that push or pull on material as they move through the Earth.

Question 30

What are secondary waves (S-waves)?

Answer 30

Cause more tremors a few minutes later. They are transverse waves that travel more slowly than p-waves. They shake the material that they pass through inside the Earth from side to side.

Question 31

What are long waves (L-waves)?

Answer 31

Arrive last and cause violent movement on the surface up and down as well as backwards and forwards. They travel more slowly than p or s waves, and they only happen in the Earth’s crust.

Question 32

Explain what happens with the waves during an earthquake.

Answer 32

P and S waves bend as they travel through the mantle. This is because their speed changes gradually with depth, and so their direction changes with depth.
P-waves refract at the boundary between the mantle and the outer core. This is because their speed changes at the boundary.
s-waves are transverse waves, and so they can’t travel through the liquid outer core.

Question 33

How does the existence of the shadow zone show that there is a liquid (outer) core under the mantle?

Answer 33

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