Edexcel GCSE Physics

Vector

A quantity that has both a size and a direction

absorption spectrum

A spectrum of light (or electromagnetic radiation) that includes black lines. These are caused by some wavelengths being absorbed by materials that the light (or radiation) passes through

acceleration

A measure of how quickly the velocity of something is changing. It can be positive if the object is speeding up or negative if it is slowing down. It is a vector quanitity.

Action - Reaction forces

Pairs of forces on interacting objects. They are always the same size, in opposite directions, and on acting on different objects.

activity

The number of emissions of ionising radiation from a sample in a given time. This is usually given in becquerels (Bq)

alpha particle

A particle made up of two protons and two neutrons, emitted as ionising radiation from radioactive isotopes.

amplitude

The size of vibrations or the maximum distance a particle moves away from its resting position when a wave passes

amplify

To make bigger

angle of incidence

The angle between an incoming light ray and the normal

angle of reflection

The angle between the normal and a ray of light that has been reflected

atom

The smallest neutral part of an element that can take part in chemical reactions

atomic number

number of protons in the nucleus of an atom

average speed

the speed worked out from the total distance travelled divided by the total time taken for a journey

background radiation

Ionising radiation that is around us all the time from a number of sources. Some of it is naturally occurring, but some comes from human activities

balanced forces

When the forces in opposite directions are the same size so that there is a zero resultant force

becquerel (Bq)

The unit for the activity of a radioactive substance. One Bq = One Radioactive decay per second

beta particle

A particle of radiation emitted from the nucleus of a radioactive atom when it decays. It is a fast moving electron.

braking distance

The distance travelled by a vehicle while the brakes are applied to bring it to a halt

centripetal force

A force that causes objects to follow a circular path. The force acts towards the centre of the circle

chain reaction

The sequence of reactions produced when a nuclear fission reaction triggers one or more fissions

cochlea

The part of the ear that changes vibrations into electrical impulses

elastic potential energy

Stored or stretched energy that can allow an object to change back to its original shape

electromagnetic waves

a group of waves that travel at the same speed in a vacuum (speed of light) and are transverse

electrostatic repulsion

a force between two charges that have the same sign that pushes them apart

emission spectrum

A set of wavelengths of light or electromagnetic radiation showing which wavelengths have been given out by a substance

external radiotherapy

treatment of cancer by sending radiation into the body from the outside

focal length

the distance from a lens to the focal point

focal point

The point at which parallel light rays converge after passing through a converging lens (or spread out in a diverging lens)

frequency

the number of vibrations (or waves) per second measured in Hertz

gamma ray

high frequency, highly penetrating electromagnetic wave emitted from the nucleus of a radioactive atom

Geiger-Muller (GM) Tube

A device that can detect ionising radiation and is used to measure the activity of a radioactive source

gravitational field strength

A measure of how strong the force of gravity is somewhere. The units are newtons per kg (N/kg)

half-life

The average time taken for half of the radioactive nuclei in a sample of radioactive material to have decayed

incident ray

a ray of light going towards an interface or object

inertial mass

Ratio of force divided by acceleration.

infrared radiation

EM radiation that we can feel as heat

infrasound

Sound waves with a frequency below 20 Hz, which is too low for the human ear to detect

instantaneous speed

The speed at one particular moment in a journey

interface

The boundary between two mediums

internal radiotherapy

Treatment of cancer by putting a radioactive source inside the body

ionising radiation

Radiation that can cause charged particles (ions) to be formed. It can cause tissue damage and DNA mutations

irradiated

when exposed to ionising radiation e.g.sterilising food/medical equipment with gamma rays

joule (J)

unit of measuring energy

kinetic energy

A term used to describe energy when it is stored in moving things

law of conservation of energy

energy can never be created or destroyed, only transferred from one store to another

law of reflection

angle of incidence = angle of reflection

light gate

apparatus use to measure speed over time

conservation of momentum

for a collision occurring between object 1 and object 2 the total momentum of the two objects before the collisions is equal to the total momentum of the two objects after collisions

contamination

unwanted addition that makes something unsuitable or impure

conduction

energy transfer through solids by heating - vibrations are passed on from particle to particle

convection

The movement of particles in a fluid (gas or liquid) depending on their temperature. Hot, less dense air rises and cold, denser air, sinks.

converging lens

A lens that brings light rays together

control rod

Absorbs neutrons in nuclear fission to slow down the nuclear chain reaction

critical angle

The angle of incidence above which total internal reflection occurs

daughter nucleus

A nucleus produced when the nucleus of an unstable atom splits into two during fission or when a radioactive nucleus by emitting an alpha or beta particle

deceleration

When an object is slowing down. A negative acceleration

diffuse reflection

Reflection from a rough surface, where the reflected light is scattered in all directions

displacement

distance in a particle direction, it is a vector.

dissipated

spread out

divereging lens

A lens that spreads out light rays

gradient of a distance/time graph

its speed

gradient of a velocity/time graph

its acceleration

longitudinal wave

A wave where the vibrations are parallel to the direction of which the wave is travelling (e.g. sound wave)

mass number

Total number of protons and neutrons in the nucleus of an atom. Also known as the nucleon number.

medium

material through which electromagnetic waves travel

moderator

A substance in a nuclear reactor that slows down neutrons, so that they can be absorbed by the nuclear fuel more easily

momentum

The mass of an object multiplied by its velocity. Momentum is a vector quantity measured in kilograms meteres per second (kg m/s)

normal

An imaginary line drawn at right angles to the suraface of a mirror or lens where a ray of light hits it

nuclear fission

The reaction in which the nucleus of a large atom, such as uranium, splits into two smaller nuclei

nucleon

A particle found in the nucleus (neutron or proton)

oscillation

movement backwards and forwards

P waves

Longitudinal seismic waves that travel through the Earth

period

The time taken for one complete wave to pass a point. It is measured in seconds. (1/t)

PET scanner

A medical scanning technique that detects gamma rays caused by the interaction of a positron from a radioactive source with an electron

Power (in energy transfers)

The amount of energy (in J) transferred every second. It is measured in Watts (W).

Power (in lens)

A measure of how much the lens bends light rays passing through it (1/focal length)

real image

An image through which light rays pass, so that it can be seen on a screen placed at that point

reaction time

The time taken to respond to a stimulus

refraction

The change in direction when a wave goes from one medium to another

resultant force

The total force that results from two or more forces acting upon a single object. It is found by adding together the forces, taking into account their directions. Another term for net force.

S waves

Transverse seismic waves that travel through the Earth

scalar quantity

A quantity that has a magnitude (size) but not a direction. Examples include mass, distance energy and speed

Shadow zone

A part of the Earth's surface that P waves or S waves from an earthquake do not reach because of the way they have been reflected or refracted within the Earth

specular reflection

When light is reflected evenly, so that all reflected light goes off in the same direction. Mirrors produce specular reflection.

stopping distance

The distance in which a car stops, which is the sum of the thinking and braking distanceq

speed

A scalar quantity (distance/time)

thinking distance

The distance travelled by a vehicle while the driver reacts

total internal reflection

The reflection of a ray of light inside a medium such as glass or water when it reaches an interface. It only happens when the angle of incidence inside the material is greater than the critical angle.

transverse

A wave where the vibrations are at right angles to the direction in which the wave is travelling

ultrasound

Sound waves with a frequency above 20kHz, which is too high for the human ear to detect

transverse wave

A wave where the vibrations are at right angles to the direction in which the wave is travelling

unbalanced forces

When the forces in opposite directions on an object do not cancel out, so there is a non-zero resultant force

upthrust

The upward force in a liquid or gas exerts on a body floating in it

tracer

A radioactive substance that is delibrately injected into the body or moving water. It allows the movement of the substance to be followed by detecting the ionsing radiation emitted

virtual image

An image that light rays do not pass through; they only appear to come from the image

Watt

Unit for Power

work done

force x distance

force

mass x acceleration

GPE

mass x gravitational field strength x height

KE

0.5 x mass x velocity2