waves

amplitude of a wave

this is "how high" the wave is from its undisturbed position, it is not crest to trough.

diffuse reflection

light is incident on a rough surface, parallel rays of light are reflected at random angles, image cannot be formed

electromagnetic waves

transverse waves that transfer energy, the electric and magnetic fields that make up an em wave oscillate perpendicular to the direction in which the wave is travelling, they form a continuous spectrum, can travel through a vacuum at the same speed

focal length

distance between the principal focus and the centre of the lens

frequency of a wave

the number of waves passing a certain point each second

gamma rays and their uses

produced when there are changes to the nuclei of atoms, they can both penetrate body tissue e.g. technetium 99m is injected into the patient's bloodstream and the gamma rays which it emits in the kidneys pass out of the body and can be detected which provides imformation to doctors on the patient's condition. can also be used to damage body tissue e.g. in radiotherapy - gamma rays emitted by iodine-131 which is swallowed by the patient can be used to treat a thyroid condition

how do we hear sound

the sound wave sets our ear drum into oscillation, this causes the small bones in the ear to oscillate, as a result an electrical signal which is produced in the cochlea is sent to the brain via the auditory nerve

image of an object formed in a plane mirror (flat surface)

virtual image, upright, appears to be the same distance behind the mirror as the object is in front of it

image of an object from a concave (diverging) lens

virtual, upright, diminished

image of object between 2f and f from a convex (converging) lens

real, inverted, magnified

image of object between f and a convex (converging) lens

virtual, upright, magnified

image of object further than 2f from a convex (converging) lens

real, inverted, diminished

law of reflection

the angle of incidence is equal to the angle of reflection

longitudinal wave e.g. sound waves, P-waves

vibrations/ oscillations are parallel to the direction of energy transfer

P-waves (primary waves)

longitudinal waves, can travel through both solid and liquid rock (travel quicker in solid rock)

perfect black body

absorbs all of the radiation that is incident onto it and doesn't reflect or transmit any of it, perfect emitter of radiation

period of a wave

the time taken for one complete wave to pass a certain point

principal focus of a convex (converging) lens

point through which light rays that are initially travelling parallel to the principal axis will travel after being refracted by the lens

refraction

the change in direction of a wave as it travels from one medium into another, it happens when a wave changes speed upon travelling from the first medium into the second

S-waves (secondary waves)

transverse waves, can only travel through solid rock not liquid rock

specular reflection

light is incident on a smooth, polished surface, parallel rays of light are reflected at the same angle, virtual image produced

transverse wave e.g. electromagnetic waves, water waves, S-waves

vibrations/ oscillations are perpendicular to the direction of energy transfer

ultrasound

sound waves with frequencies above 20kHz, each time they arrive at a boundary between one material and another, they will be partially transmitted and partially reflected, the time delay between sending and receiving an ultrasonic pulse allows the depth of a given boundary within the object to be determined

ultraviolet rays and fluorescence

a fluorescent substance can absorb uv radiation and use its energy for the emission of longer-wavelength visible light

uses of infrared radiation

electrical heaters, cookers, remote controls, infrared cameras, some fibre-optic communications

uses of microwaves

cooking food, mobile phone networks, satellite communications (pass easily through earth's atmosphere), short range bluetooth communication

uses of radio waves

radio and television signals, radar

uses of visible light

human sight, lasers, fibre-optic communications

virtual image

an image that cannot be projected onto a screen

wave

transfers energy from one place to another without a permanent motion of the material which it is travelling through

wavelength

this is the distance between two corresponding points on the wave and is measured in metres. the two points can be crest to crest, trough to trough

what happens when a wavefront travels from deep water into shallow water

the frequency of the wave stays the same however the wavelength is shorter is shallow water because the waves travel more slowly, the speed of a wave is directly proportional to its wavelength

x-rays and their uses

produced by the rapid deceleration of free electrons, they pass easily through soft body tissue but are absorbed effectively by bone so are used in medical imaging. can also damage body tissue so are used in medical treatment to control or kill tumours

longitudinal waves

• oscillations are parallel to the direction of travel of the wave

• sound waves

features of a wave

wave equation