Waves & Radiation: Waves

Question 1

Define a ‘transverse’ wave, and provide examples.

Answer 1

A ‘transverse’ wave is a wave in which the medium vibrates at right angles to the direction of its propagation.

Some examples of transverse waves are water, and any member of the EM spectrum.

Question 2

Define a ‘longitudinal’ wave, and provide examples.

Answer 2

A ‘longitudinal’ wave is a wave vibrating in the direction of propagation.

An example of a longitudinal wave is sound.

Question 3

Describe these basic wave properties: Crest, Trough, Wavelength, Amplitude.

Answer 3

The crest is the highest point on a wave.

The trough is the lowest point on a wave.

The wavelength is the distance until a wave repeats itself.

The amplitude is the height of the wave from the rest position.

Question 4

What is the ‘wave equation’, which links wavelength, frequency, and speed?

Answer 4

The wave equation is ‘v = fλ’

(velocity = frequency * wavelength)

Question 5

What is the frequency of a wave, and what is the equation we can use to find it?

Answer 5

The frequency of a wave is the number of waves produced in one second.

This is the same as the number of waves that pass a point in one second.

It is measured in hertz (Hz).

The ‘frequency’ equation is F=N/t

(Frequency = number of waves passing a point / time)

Question 6

What is the period, and what formula can we use to calculate it?

Answer 6

The period is the time it takes for one complete wave to pass a point.

The ‘Period’ formula is T = 1/f

(Period = 1 / frequency)

Question 7

What medium can light not travel through?

Answer 7

Light cannot travel through a vacuum.

Question 8

Describe an experiment which measures the speed of sound in air.

Answer 8

Two microphones are placed at a set distance away from each other, this distance is measured (d).

A sound is made which travels through both microphones. The time it takes between the sound being picked up by each microphone is your time (t).

The formula (v = d/t) is used, linking the distance and time we have measured providing us the speed.

Question 9

What is the speed of sound in air, roughly?

Answer 9

The speed of sound in air is roughly (by SQA standards) 340ms^-1.

Question 10

What is the speed of light in air, roughly?

Answer 10

The speed of light in air is roughly (by SQA standards) 3x10⁸ms^-1.

Question 11

Provide an example proving that the speed of light is faster than the speed of sound.

Answer 11

An example which can prove that the speed of light is faster than the speed of sound is lightning and thunder.

In a thunder storm, you will always see the lightning before the thunder.

This is because the storm could be kilometres away, yet the speed of sound can only travel a kilometre in about 3 seconds, whereas light will arrive near instantly.

Question 12

State the members of the Electromagnetic Spectrum in order of increasing wavelength.

Answer 12

Gamma, X-rays, Ultraviolet, visible light, infrared, microwaves, radio waves.

Question 13

What can be said about the speed of all Electromagnetic Waves?

Answer 13

All Electromagnetic Waves travel at the speed of light (3x10⁸ms^-1).

Question 14

State a suitable use for ‘Infrared Radiation’.

Answer 14

A use for ‘Infrared Radiation’ would be IR cameras on police helicopters.

Infrared cameras take in the heat (infrared) that is emitted from an object, and provide a certain colour based on the specific heat.

Humans have a fairly high body temperature, and therefore can be picked up by these cameras quite easily.

Question 15

State 2 suitable uses for ‘Ultraviolet Radiation’, and briefly describe its source & risks.

Answer 15

A use for ‘Ultraviolet Radiation’ would be sun beds and security pens.

Ultraviolet is found naturally in sunlight, and it causes tanning and burning of skin.

Overexposure to Ultraviolet Radiation can lead to skin cancer.

‘Sun beds’ allow for cosmetic tanning of the skin.

‘Security pens’ check for forged banknotes in banks & other areas.

Question 16

State a suitable use for ‘X-rays’, and briefly describe its risks.

Answer 16

A use for ‘X-rays’ would be the detection of broken/fractured bones.

X-rays can pass through skin and soft tissue, but cannot easily pass through bone or metal.

X-rays are used in hospitals to detect broken bones in patients.

Hospitals can use photographic film to detect these X-rays.

Overexposure to X-rays can cause cancer. Hospitals must limit the dose received by patients and staff.

Question 17

What happens to a light ray when it leaves an ‘optically denser’ medium?

Answer 17

When a light ray leaves an ‘optically denser’ medium, it speeds up. This is called refraction.

e.g. Glass to Air - 2x10⁸ms^-1 → 3x10⁸ms^-1.

If the ray is travelling at an angle not directly at the normal, it will bend away from it.

Question 18

State 2 suitable uses for ‘Gamma Radiation’, and briefly describe its risks.

Answer 18

A use for ‘Gamma Radiation’ would be sterilization and destroying cancerous cells.

Gamma radiation can pass through skin and soft tissue, but some of it is absorbed by cells.

Gamma radiation can kill or damage cells, meaning it can lead to cancer if too much is absorbed.

Gamma is used to sterilize surgical equipment because it can kill bacteria.

High doses of Gamma is concentrated on a patient’s cancerous tumour in order to kill it.

Question 19

What is ‘total internal reflection’?

Answer 19

‘total internal reflection’ is the complete reflection of a ray of light within a medium.

Question 20

State a suitable use for ‘Radio Waves’. (Make sure to briefly describe what an AM & FM wave is)

Answer 20

A use for ‘Radio Waves’ would be radio stations.

A radio station is defined by the frequency of the signal it transmits.

As we know, the speed of sound is much slower than the speed of light.

When you listen to a radio, what you hear is carried by AM (Amplitude Modulated) or FM (Frequency Modulated) radio waves.

AM & FM Waves modify its characteristics to be able to carry sound, meaning it is able to travel at the speed of light.

Question 21

State a suitable use for ‘Microwaves’.

Answer 21

A use for ‘Microwaves’ would be mobile networking.

They are used to transmit information such as mobile phone calls.

Microwave transmitters and receivers on buildings and masts communicate with phones in their range.

Question 22

What happens to a light ray when it enters an ‘optically denser’ medium?

Answer 22

When a light ray enters an ‘optically denser’ medium, it slows down. This is called refraction.

e.g. Air to Glass - 3x10⁸ms^-1 → 2x10⁸ms^-1.

If the ray is travelling at an angle not directly at the normal, it will bend towards it.

Question 23

Describe these parts of a ray diagram: Normal, angle of incidence, angle of refraction, incident ray, refracted ray.

Answer 23

The normal is a line drawn at 90 degrees to the medium.

The angle of incidence is the angle at which the ray enters the medium from the normal.

The angle of refraction is the angle at which the ray leaves the medium from the normal.

The incident ray is the ray which enters the medium.

The refracted ray is the slowed down ray.

Question 24

What is the ‘Critical Angle’?

Answer 24

The critical angle is the minimum angle at which total internal reflection occurs.

This changes depending on the medium, it can be measured via experiment.

Question 25

What is an application of ‘total internal reflection’?

Answer 25

An application of ‘total internal reflection’ would be optical fibre cables.

Light is totally internally reflected along the cable to reach its destination.

Question 26

Describe the effect of a converging (convex) and diverging (concave) lenses on parallel light rays.

Answer 26

Convex (converging) lenses converge light to a focal point.

Concave (diverging) lenses spread light out.

Question 27

What is diffraction, and what is the difference of diffraction of shorter and longer wavelengths?

Answer 27

Diffraction is the bending of waves around an object.

Longer wavelengths diffract more.

Shorter wavelengths diffract less.

Question 28

What is a wave?

Answer 28

A wave is moving energy.