GCSE OCR Physics P5

Amplitude

distance from the middle to the top of the wave of bottom of a wave.

height of the wave

Wavelength

distance between one point on a wave to the same point on the next wave

metres

Frequency

number of waves/oscillation per second

measured in Hz

time period

the time it takes for one wave to pass a given point

mechanical waves

require a medium to travel through

non-mechanical waves

Waves that do not require a medium

wave velocity m/s

frequency hz x wavelength m

how to measure wave velocity of ripples

Use ripple tank

find wavelength by using flashing light and a ruler

fin frequency by finding the number of rotations by the motor per second.

Transverse waves features

the direction of vibrations are perpendicular to the direction of travel of the wave

EM Waves S waves Ripples in water

Longitudinal waves features

the direction of vibrations are parallel to the direction of travel of the wave

Sound Waves ,P waves

When sound travels across a boundary

refraction occurs

-velocity changes

-direction changes

the direction changes so it moves away from the normal.

frequency stays the same

wavelength and velocity increases

what happens when a sound hits a boundary (RAT)

reflected (echo)

absorbed

transmitted

what actually happens is dependent on the densities of the regions either side of the boundary

With sound waves if the densities are different then

more of the sound will be reflected

how to measure the velocity of sound

connect a pair of microphones a certain distance apart to an oscilloscope

make sure you know the distance

What is ultrasound?

a frequency greater than 20,000 Hz

useful because it has a very small wave length and so can be focused into a beam

ultrasound

transmitter beams US waves into the mother

the waves reflect from different boundaries

machine calculates the distances using time and velocity and uses those to produce an image of the internal structures i.e foetus

in an ultrasound

Lighter parts signify denser tissue and darker parts signify less dense tissue like skin

sonar

transmitter sends out an impulse and calculates the distance from the time of the echo picked up by the receiver

State some of the uses of infra red rays

thermal imaging

short range comms

cooking + optical fibres

security systems

How does your ear detect sound

1. the outer ear (pinna + auditory canal) gather sound waves and directs them to the ear drum

2. As the ear drum vibrates ossicles vibrate which amplify the vibration and pass it on to the inner ear through the oval window

3. small hairs on the wall of the cochlea transmit the sound from the oval window to the cochlea.

4. these small hairs are attached to sound detecting cells which release chemical substances

5. this sends a signal down your auditory nerve

6. Brain processes the signal and you hear the sound

middle ear

ear drum,

Hammer Anvil Stirrup (ossiscles)

Oval window

inner ear

cochlea and auditory nerve

outer ear

pinna and auditory canal

it is the wave and not the water that travels

you can see this by putting a small cork in the water

it is the wave and not the air that travels

shown because when you speak the air does not move away from your mouth

All electromagnetic waves have the same

velocity

electromagnetic waves transfer energy from

a source to an absorber

i.e the sun ( a source) emits EM Waves and this is absorbed by the skin(absorber)

As you go down the EM SPECTRUM

Frequency increases and wavelength decreases

gamma has the biggest frequency but smallest wavelength)

RMIVUXG

Radio waves, microwaves, infrared waves, visible light, ultraviolet rays, gamma rays.

Our eyes can only

detect a limited range of the EM Spectrum called visible light

Electromagnetic waves are

transverse waves and are emitted through space.

Uses of radio waves

AM Radio, FM Radio, Television, Cell phones

Uses of infrared

CDs. Optical Fibre communications. Remote Controls. Night vision/ thermal imaging,ovens

State some of the uses of ultra violet rays

Flourescent lamps

detecting forged notes

sterilises water ( kills bacteria)

helps to produce vitamin D

detecting bodily fluids

State some of the uses of gamma rays

Sterilising equipment because it kills bacteria

detection of cancer and treatment it kills cancer cells

State 2 uses of microwaves

communication from satellites and TV

microwaves

Dangers of EM waves

UV can damage the DNA in skin cells which can cause cancer.

If your eyes are exposed to UV u can develop cataracts which make your cornea cloudy

X rays can damage cells and cause cancer

Gamma rays can damage and kill cells in your body

radio waves can be produced or induced (by themselves)

by oscillations in electrical circuits

an oscillating potential difference across a wire causes electrons to move back and forth making a changing electric and magnetic field.

this is emitted as a radio wave

Every EM wave has a speed of

3 * 10^8

How are infrared waves used for medical imaging?

Used by a thermal imaging camera to make a thermogram

thermograms show problems with blood flow in blood vessels and tell you whether your body is hot due to infection or radiation.

How are x rays used for imaging?

x-rays can show if your arm is broken

bones absorb x rays but skin and muscles don't

can show the internal structure of a person

can be used to diagnose problems with teeth

How are gamma rays used for imaging?

used as tracers and treat problems with organs

Briefly descirbe how a gamma camera works?

Patient ingests chemical that emits gamma rays which pass through tissue. Gamma camera detects the rays using lead and processes them to form an image

why are EM waves refracted? (explained by light)

when light goes from air to glass( a denser medium) it will slow down and bend towards the normal

The bigger the difference in density

the bigger the change in direction

A convex lens refracts light to a

principal focus

focal length in convex lens

is from optical centre to principal focus

(half the lens to the bit where the lines join up)

concave lens

spreads light rays out

the focal length in concave lens

virtual focus to the optical centre

ray diagram of a real image

ray diagram of a virtual image

amplifies the real image size

What is the period of the wave and its equation?

Number of seconds for 1 full cycle

period = 1/frequency

What happens when white light is refracted through a prism and why?

Colour spectrum appears on opposite side(ROYGBIV). This happens due to 2 points of refraction in prism which are more dense than air and since different lights have different wavelengths each refracts a certain amount/angle

specular reflection

a reflection produced by a smooth surface in which parallel light rays are reflected in parallel

diffuse reflection

Reflection that occurs when parallel rays of light hit a rough surface and all reflect at different angles

What is a real/virtual image?

Real image = light comes from object to form an image on screen like a retina

Virtual image = when rays are diverging so light from the object appears to be coming from a completely different place (eg mirror)

What happens to a light ray if it travels into a more dense material?

It will slow down making it bend towards the normal

What happens to a light ray if it travels into a less dense material?

It will speed up making it bend away from the normal

Describe the direction of light waves in the following lenses

convex

normal

concave

convex = rays go inwards

normal = rays maintain direction

concave = rays go outwards