P1.5.1 General Properties of Waves

Question 1

Waves transfer _ _ _ _ _ _ from one place to another without transferring any _ _ _ _ _ _.

Answer 1

Waves transfer energy from one place to another without transferring any matter.

Question 2

What vibrations do transverse waves have?

Answer 2

In a transverse wave the oscillations are perpendicular to the direction of energy transfer (If the wave was travelling straight to the right or the left, the vibrations would be from side to side).

Question 3

What vibrations do longitudinal waves have?

Answer 3

In a longitudinal wave the oscillations are parallel to the direction of energy transfer (If the wave was travelling straight to the right or the left, the vibrations would be in the same directions.)

Question 4

Sound waves: transverse or longitudinal?

Answer 4

Longitudinal.

Question 5

Electromagnetic waves: transverse or longitudinal?

Answer 5

Transverse.

Question 6

Mechanical waves: transverse or longitudinal?

Answer 6

The can be both.

Question 7

Longitudinal waves show areas of _ _ _ _ _ _ _ _ _ _ _ and _ _ _ _ _ _ _ _ _ _ _.

Answer 7

Longitudinal waves show areas of compression and rarefaction.

Question 8

Electromagnetic waves form a _ _ _ _ _ _ _ _ _ _ spectrum.

Answer 8

Electromagnetic waves form a continuous spectrum.

Question 9

What is the order of electromagnetic waves within the spectrum, mentioning the energy, frequency and wavelength?

Answer 9

The order of electromagnetic waves within the spectrum:
—> Increasing frequency
—> Increasing energy
—> Decreasing wavelength
Radiowaves, Microwaves, Infrared, Visible Light, Ultraviolet, X-Rays, Gamma Rays

Question 10

All types of electromagnetic waves travel at the _ _ _ _ speed through a _ _ _ _ _ _ (space).

Answer 10

All types of electromagnetic waves travel at the same speed through a vacuum (space).

Question 11

Wavelengths vary from _ metres to more than _ metres.

Answer 11

Wavelengths vary from 10(-15) metres to more than 10(4) metres.

Question 12

EM waves with higher _________ have shorter _______.

Answer 12

EM waves with higher frequencies have shorter wavelengths.

Question 13

Name the three ways that waves can change direction when they meet an obstacle (or a new material).

Answer 13

1. Reflected
2. Refracted
3. Diffracted

Question 14

What is diffraction?

Answer 14

When waves meet a gap in a barrier, they carry on through the gap. However all waves spread out at the edges, to some extent, when they pass through a gap or pass an obstacle, into the area beyond the gap. This is diffraction.

Question 15

What two things does the amount of diffraction depend on?

Answer 15

The amount of diffraction depends on the size of the gap, relative to the wavelength of the wave.

Question 16

The _________ the gap, or the ________ the wavelength, the _____ the wave spreads out.

Answer 16

The narrower the gap, or the longer the wavelength, the more the wave spreads out.

Question 17

Under what circumstances does significant diffraction occur?

Answer 17

Significant diffraction only occurs when the wavelength of the wave is the same order of magnitude as the size of the gap or obstacle.

Question 18

What determines a gap as being narrow?

Answer 18

A narrow gas is one that is the same order of magnitude as the wavelength of the wave - i.e. they’re about the same size. Therefore, whether a gap is narrow or not depends of the wave in question.

Question 19

What is refraction?

Answer 19

Waves undergo a change of direction when they are refracted at an interface - i.e. when a wave crosses a boundary between two substances, it changes direction - but only if it meets the new medium at an angle.

Question 20

When are waves not refracted?

Answer 20

Waves are not refracted if travelling along the normal.

Question 21

What happens if waves travel along the normal when crossing a boundary?

Answer 21

They aren’t refracted, but the wave does change speed.

Question 22

What is the amplitude?

Answer 22

The amplitude is the displacement from the rest position to the crest (NOT from the trough to a crest).

Question 23

What is the wavelength and what is the unit?

Answer 23

The wavelength is the length of a full cycle of the wave (e.g. from crest to crest or from trough to trough). The wavelength is usually in metres.

Question 24

What is frequency and what is the unit?

Answer 24

Frequency is the number of complete waves passing a certain point per second OR the number of waves produced by a source each second. The frequency is measured in hertz (Hz). 1 Hz is 1 wave per second.

Question 25

Which equation do all waves obey? Give the units.

Answer 25

Speed (meters per second, m/s) = Frequency (hertz, Hz) × Wavelength (meters, s)

Question 26

Name four waves that can used in one way.

Answer 26

Radio waves, microwaves, infrared waves and visible light can be used for communication.

Question 27

Explain the uses of long-wave radio for communications.

Answer 27

• Long-wave radio wavelengths (1 - 10 km) can diffract around the curved surface of the earth, including around hills and into tunnels.
• This diffraction effect makes it possible for radio signals to received even if the receiver isn’t in line of the sight of the transmitter.

Question 28

Explain the uses of short-wave (or medium) radio for communications.

Answer 28

• Short-wave radio signals (10 - 100 m) can, like long-wave, be received at long distances from the transmitter.
• That’s because they are reflected from the ionosphere.
• Medium-wave signals can also reflect from the ionosphere, depending on atmospheric conditions and the time of day.

Question 29

Explain the uses of very short-wave radio for communications.

Answer 29

• The radio waves for TV and FM radio transmissions have very short wavelengths (10 cm - 10 m).
• To get reception, you must be in direct sight of the transmitter. The signal doesn’t bend around hills or travel far through buildings.

Question 30

What is the ionosphere?

Answer 30

The ionosphere is an electrically charged layer in the Earth’s upper atmosphere.

Question 31

Give two uses of microwaves in communication.

Answer 31

1. Satellite communication

2. Mobile phones

Question 32

Why are microwaves better for satellite communication rather than radio waves?

Answer 32

Microwaves which can pass easily through the Earth’ watery atmosphere are needed - radio waves can’t do this.

Question 33

Explain how microwaves are used in satellite TV and mobile phone calls.

Answer 33

For satellite TV:
1. The signal for a transmitter is transmitted into space…
2. …where it’s picked up by the satellite’s receiver dish orbiting above Earth.
3. The satellite transmits the signal back to Earth in a different direction…
4. …where it’s received by a satellite dish on the ground.
For mobile phones:
Calls can also travel as microwaves between your phone and the nearest transmitter. The process is essentially the same then.

Question 34

Why do some people think that mobile phones can be a hazard to people’s health?

Answer 34

Some wavelengths of microwaves are absorbed by water molecules and heat them up. If the water in question happens to be in you cells, they might start to heat up - therefore some people think that using you phone a lot or living near a mast, could damage your health.

Question 35

Why are microwaves used by remote-sensing satellites?

Answer 35

To ‘see’ though the clouds and monitor:

• oil spills
• track the movement of icebergs
• see how much rainforest has been chopped down and so on.

Question 36

Explain two ways in which infrared waves can be used.

Answer 36

1. Remote controls

2. Optical fibres

Question 37

How are infrared waves used in remote controls?

Answer 37

Wireless remote controls work by emitting different patterns of infrared waves to send different commands to an appliance.

Question 38

How are infrared waves and visible light used in optical fibres?

Answer 38

• Optical fibres c(e.g. those used in phone lines) an carry data over long distances very quickly.
• The signal is carried as pulses of light or infrared radiation and is reflected off the sides of a very narrow core from one end to the other.

Question 39

Give one use of visible light.

Answer 39

Photography.

Question 40

Explain how photography works.

Answer 40

1. Cameras use lens to focus visible light onto a light sensitive film or electronic sensor.
2. The lens aperture controls how much light enters the camera.
3. The shutter speed determines how long the film or sensor is exposed to the light.
4. By varying the aperture, shutter speed and sensitivity of the film/sensor, a photographer can capture as much or as little light as they want in their photograph.