topic 6 waves

what do waves do

transfer energy in the direction they are travelling

• they can all be absorbed, transmitted or reflected

• particles vibrate to transfer energy when waves pass through a medium

transverse waves

amplitude definition

height from rest position

wavelength definition

distance of point on 1 wave to same point on next wave

what are transverse waves perpendicular to

energy transfer

transverse waves example

The ripples on a water surface are an example of a transverse wave.

longditudinal waves

what is longitudinal waves direction of energy transfer

parallel vibration to direction of energy vibration

example of longitudinal waves

sound waves in air and seismic shock waves

what is rarefaction

region where the particles of the medium are spread furthest apart

compression definition

where the particles are packed closely together

longitudinal wavelength definition

gap between 2 rarefactions or compressions

what is wave frequency

the number of waves passing a point each second in Hz

what is the wave speed

the speed at which the energy is transferred (or the wave moves) through the medium in SECONDS

method to measure speed of sound waves in air

a person fires a starting pistol and raises their hand in the air at the same time.

A distant observer stood 400 metres away records the time between seeing the action (the light reaches the time keeper immediately) and hearing the sound (which takes more time to cover the same distance) - shows light travels faster than sound

The speed of sound can be calculated using the equation: speed = distance/time

flaws of this method

humans do not use stop clocks identically to one another/human error

The values recorded will be dependent on the reaction time of the observer, and will not be entirely accurate

relationship between frequency and wavelength

inversely proportional

• freq double = wavelength halves

Required practical - measuring waves in a ripple tank

1. Set up the ripple tank as shown in the diagram with about 5 cm depth of water.

2. Adjust the height of the wooden rod so that it just touches the surface of the water.

3. Switch on the lamp and motor and adjust until low frequency waves can be clearly observed.

4. Measure the length of a number of waves then divide by the number of waves to record wavelength. It may be more practical to take a photograph of the card with the ruler and take measurements from the still picture.

5. Count the number of waves passing a point in ten seconds then divide by ten to record frequency.

6. Calculate the speed of the waves using: wave speed = frequency × wavelength.

hazards from measuring waves in tank

electrical components near water risk of shock or damage to components

ensure to secure electrical components before adding water taking care not to splash

measuring waves in a solid

what happens down the electromagnetic spectrum

wave length decreases and freq increases

what type of waves are electromagnetic waves and what do they transfer energy from and to

transverse waves

from source to absorber

what do EM waves all have same in vacuum or through air

speed

which light can humans see

visible light

what is the speed of light

3 × 10^8

uses of radiowaves

Why: Long wavelength → can travel long distances and around obstacles easily. Can carry information over large areas.

radio communication

bluetooth

TV

uses of microwaves

Why: Can pass through the atmosphere for satellites. At certain frequencies, water molecules absorb energy efficiently → heats food.

satellites

microwave ovens

uses of infra red

Why: Infrared is thermal radiation → efficiently transfers heat. Detected as heat by infrared cameras.

monitor temperatures

thermal cameras

uses of visible light

Why: Short wavelength → can be guided through thin fibres with very low loss. Carries information as pulses of light.

fibre optics - carry data

uses of ultra violet

Why: High energy → excites electrons in materials (makes lamps glow) and stimulates skin to produce vitamin D/tan.

sun tan

invisible pens

fluorescent lights

uses of xrays

Why: Very high energy → can penetrate soft tissue (X-rays) for imaging and destroy cancer cells (gamma rays) in treatments.

medicine in radiography

uses of gamma rays

Why: Very high energy → can penetrate soft tissue (X-rays) for imaging and destroy cancer cells (gamma rays) in treatments.

medical tracers

what is radiation risk measured in

sieverts

why are high freq waves dangerous n examples

they transfer lots of energy so can be harmful - UV XRAYS AND GAMMA

why r low freq waves not so dangerous

waves like radio waves do not transfer much energy and pass soft tissue without absorption

what does uv do to skin

damages surface cells, leads to sunburn and increases skin cancer chance

relation between velocity, frequency and wavelength, in transmission of sound waves from one medium to another

• When a sound wave moves from one medium (like air) to another (like water), its speed changes.

• The frequency of the sound stays the same, but because speed changes, the wavelength changes.

These three - speed, frequency, and wavelength—are related by the equation:

speed = freq x wavelength

So if you know any two of these variables, you can find the third.

why does speed change but frequency stays same in different mediums

Because frequency is determined by the source of the sound, not the medium

what can happen to waves at the boundary between 2 different materials

Waves can be reflected at the boundary between two different materials and can be absorbed or transmitted at the boundary between two different materials