waves

Question 1

transverse waves

Answer 1

A transverse wave is one where the direction of vibration is perpendicular to the direction of energy transfer.
e.g. water waves, Electromagnetic waves, S waves

Question 2

longitudinal waves

Answer 2

A longitudinal wave is one where the direction of vibration is parallel to the direction of energy transfer.

e.g. sound waves (in air), p waves

Question 3

Wave properties

Answer 3

For both ripples on a water surface and sound waves in air, it is the wave and not the water or air itself that travels.

Question 4

amplitude

Answer 4

The amplitude of a wave is the maximum displacement of a point on a wave away from its undisturbed position.

for transverse waves

Question 5

wavelength

Answer 5

The wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave.

for transverse waves

Question 6

frequency

Answer 6

The frequency of a wave is the number of waves passing a point each second.

Question 6

The Wave Equation

Answer 6

𝑤𝑎𝑣𝑒𝑠𝑝𝑒𝑒𝑑=𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦×𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ
𝑣=𝑓𝜆
v: m/s
f: Hz
λ: m

Question 7

Time Period

Answer 7

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

𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 (Hz) =1/(𝑡𝑖𝑚𝑒 𝑝𝑒𝑟𝑖𝑜𝑑 - s)
𝑓=1/𝑇

Question 8

specular reflection

Answer 8

Question 9

diffuse reflection

Answer 9

Question 10

how is an image formed by a mirror

Answer 10

Question 11

Describe a method that can be used to measure the speed of sound in air:

Answer 11

two people (person A and person B) are placed a distance apart, eg 100 metres
person A fires a starter’s pistol (or hitting two blocks of wood)
person B times the difference between seeing the flash of the gun and hearing the sound - this is measured in seconds
The speed of sound can be calculated using this equation:

𝑠𝑝𝑒𝑒𝑑=𝑑is𝑡𝑎𝑛𝑐𝑒/𝑡𝑖𝑚𝑒

Question 12

Sound waves

Answer 12

Sound waves can travel through solids causing vibrations in the solid.
Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound. The conversion of sound waves to vibrations of solids works over a limited frequency range of 20 to 20 000 Hz. This restricts the limits of human hearing.

Question 13

Ultrasound

Answer 13

Ultrasound waves have a frequency higher than the upper limit of hearing for humans. Ultrasound waves are partially reflected when they meet a boundary between two different media. The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is. This allows ultrasound waves to be used for both medical and industrial imaging.

Question 14

Seismic Waves

Answer 14

Seismic waves are produced by earthquakes. There are P - waves and S - waves. P-waves and S-waves provide evidence for the structure and size of the Earth’s core.

Question 15

P - waves

Answer 15

P-waves are longitudinal seismic waves. P-waves travel at different speeds through solids and liquids.

Question 16

S - waves

Answer 16

S-waves are transverse seismic waves. S-waves cannot travel through a liquid.

Question 17

Echo Sounding

Answer 17

Echo sounding, using high frequency sound waves is used to
detect objects in deep water and measure water depth.

Question 17

The Electromagnetic Spectrum

Answer 17

Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber.
Electromagnetic waves form a continuous spectrum and all types of electromagnetic wave travel at the same velocity through a vacuum (space) or air.

The waves that form the electromagnetic spectrum are grouped in terms of their wavelength (long to short) and their frequency (low to high frequency):

Radio waves, Microwaves, Infrared, Visible Light, Ultra Violet, X-rays, Gamma Rays

Our eyes only detect visible light and so detect a limited range of electromagnetic waves.

Question 18

Radio

Answer 18

Radio waves can be produced by oscillations in electrical
circuits. When radio waves are absorbed they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical circuit. Radio waves are reflected by ionosphere (and ground) so can travel around the Earth.
uses: television and radio

Question 19

Microwave

Answer 19

When microwaves are absorbed by water they cause the water molecule to vibrate faster. Because they are not easily absorbed by water they are able to penetrate several cm into food. They can penetrate the ionosphere
uses: satellite communications, cooking food

Question 20

Infrared

Answer 20

All object emit infrared radiation, the hotter they are the more radiation is emitted
When the surface of an object absorbs infrared radiation it causes the molecules on the surface to vibrate faster.

uses: electrical heaters, cooking food, infrared cameras

Question 21

visible light

Answer 21

Light reflects off the internal edges of
fibre optic cables.

Question 22

Ultra Violet

Answer 22

UV is produced inside energy efficient bulbs. This is absorbed by the white coating on the surface of the bulb, which then emits the energy as visible light. (Fluorescence).
uses: energy efficient lamps, sun tanning,
dangers: ionising - can cause skin cancer

Question 23

X-ray

Answer 23

X-rays can penetrate soft tissue (such as muscle) but not bone (absorbed by bone).
X-rays are ionizing radiation that can cause the mutation of genes and cancer, but can also kill cancer cells
uses: medical imaging and treatments
dangers: ionising - can cause cancer

Question 24

Gamma Ray

Answer 24

Gamma are ionizing radiation that can cause the mutation of genes and cancer, but can also kill cancer cells and can kill bacteria (e.g. they can sterilize surgical equipment)
uses: medical imaging and treatments,
dangers: ionising - can cause cancer

Question 25

Refraction

Answer 25

refraction, is due to the difference in velocity of the waves in different substances.
If a wave slows down it bends towards the normal
if a wave speeds up it bends away from the normal
When a wave changes speed is wavelength changes, but its frequency always remains constant.

Question 26

refraction wavefronts

Answer 26

The wave travels faster in the first medium.
Side A of the wave (front) enters the new medium first so slows down.
But side B continues at a higher speed, so travels a greater distance in the same timw.
This causes a change in direction of the wave fronts.
The wavelength is shorter after it has crossed the boundary meaning that the wave must be slowing down

Question 27

Visible Light

Answer 27

Each colour within the visible light spectrum has its own narrow band of wavelengths and frequencies.
Colour filters work by absorbing certain wavelengths (and colours) and transmitting other wavelengths (and colours).
The colour of an opaque object is determined by which wavelengths of light are more strongly reflected. Wavelengths that are not reflected are absorbed. If all wavelengths are reflected equally the object appears white. If all wavelengths are absorbed the objects appears black.

Question 28

Global Warming

Answer 28

A body at constant temperature is absorbing radiation at the same rate as it is emitting radiation. The temperature of a body increases when the body absorbs radiation faster than it emits radiation.

Carbon dioxide (and other greenhouse gases) reduces the rate at which radiation is emitted into space, which means that the Earth absorbs more radiation than it emits causing it to increase in temperature.

As the Earth becomes hotter it emits more radiation until, eventually, the amount emitted into space becomes equal to the amount being absorbed.

Question 29

Black Body Radiation

Answer 29

All bodies (objects), no matter what temperature, emit and absorb infrared radiation. The hotter the body, the more infrared radiation it radiates in a given time.

A perfect black body is an object that absorbs all of the radiation incident on it. A black body does not reflect or transmit any radiation. Since a good absorber is also a good emitter a perfect black body would be the best possible emitter.

graph to show the distribution of wavelengths emitted by a black body for two objects at different temperatures:

Question 30

convex lenses

Answer 30

Question 31

concave lens

Answer 31