OCR A Level Physics Glossary

Absolute zero

Zero on the thermodynamic temperature scale, or 0 K (kelvin),

where a substance has minimum internal energy,

and is the coldest possible temperature.

It is equal to -273.15 degrees Celsius.

Absorption spectrum

A spectrum of dark lines across the pattern of spectral colours

produced when light passes through a gas

and the gas absorbs certain frequencies depending on the elements in the gas.

Acceleration

The (instantaneous) rate of change of velocity in respects to time.

Acceleration of free fall (g)

The acceleration of a body falling under gravity (9.81ms-2 on earth).

Ammeter

A device used to measure the electric current in a circuit. It is connected in series with the components.

Ampere

The SI unit for electric current.

Amplitude

The maximum displacement of a wave from its rest/mean position (measured in metres).

Antiphase

Any odd integer of π radians apart (for points in waves)

Attenuation

The gradual loss of flux intensity through a medium.

Attenuation coefficient

Measure of how much an incident energy beam (ultrasound or x-ray) is attenuated through a medium.

I = I0e-μx

Astronomical Unit (AU)

Average distance from the Earth to the Sun. ≈ 1.5 x 10 ^11 m

Atomic mass unit, u

An atomic mass unit is equal to the mass of 1/12th the mass of one carbon-12 atom.

Archimedes' Principle

For an object submerged in a fluid, the up-thrust is equal to the weight of that the object displaces.

Average Speed (v)

Rate of change in distance (m) calculated over a completed journey, with respect to time. Measured in ms-1.

Antinode

A point of maximum amplitude along a stationary wave

caused by constructive interference.

Angular velocity, ω

Rate of change of angle, measured in rads-1

Aphelion

The furthest point in an elliptical orbit from the sun.

Activity

Rate at which nuclei decay or disintegrate.

It is also the number of alpha, beta or gamma photons emitted per unit time.

Measured in Becquerels. Bq

Acoustic impedance (Z) Z = ρc

Fraction of ultrasound intensity reflected at the boundary depends on the acoustic impedance (Z) of both media.

Product of density (P) of substance and speed of ultrasound (c) in it.

Braking Distance

Distance travelled from the brakes being applied to the car stopping completely.

Baryon

Hadron composed of 3 quarks.

Brownian motion

Random motion of a larger particle in a gaseous system due to collisions with smaller particles.

Bremsstrahlung (or Braking) Radiation

Form of X-ray radiation produced when high energy electrons interact with a nucleus.

Black body radiation

At any given temperature above absolute zero, an object emits emr at different wavelengths and intensities.

Boyle's Law

A gas law stating a gas' pressure is inversely proportional to the volume, considering temperature is constant.

Boltzmann constant, k

A constant describing the ratio between the ideal gas constant (R/Na)

~ 1.38 x 10-23 m2kgs-2K-1

Binding Energy ΔE=Δmc2

Minimum energy required to completely separate a nucleus into its constituent protons and neutrons.

Binding energy per nucleon

Measure of stability.

The greater the value, the more tightly bound the nucleons,

the more energy needed to break them.

Charge (Q)

How much positive or negative the charge carriers are per unit volume.

Measured in coulombs.

Capacitor

An electrical component

which can separate (store) charge on two metallic plates

separated by an insulator (dielectric).

Capacitance (C)

The amount of charge per volt that can be stored.

Measured in Farads.

Chemical Energy (Ec)

Energy contained within the chemical bonds between atoms and molecules.

Characteristic Radiation

Form of X-ray radiation produced

when high energy electrons interact with electrons in orbitals around a nucleus

causing a transition of another electron to fill its gap.

Coefficient of Friction (μ)

Ratio between the frictional force and normal contact force acting on an object.

Conservation of Energy Law

Total energy in a closed system of interacting objects remains constant

can be transferred into alternate forms.

Conservation of Momentum Law

For a closed system of interacting objects,

the total momentum in a specified direction remains constant considering no external resultant force acts on it.

Conventional current

The concept of current as the transfer of positive charge

. I.e. from ve+ to ve- in a circuit.

Contrast medium μ α Z3

Used to improve visibility of soft-tissues in x-rays.

e.g. iodine and barium compounds: due to large atomic number.

Cosmological Principle

When viewed on a large scale,

the universe is homogenous and isotropic,

the laws of physics are universal.

Coulomb's Law

The force between two charges is directly proportional to the product of the charges

and inversely proportional to the distance between them squared

Conductor

A material that allows the transfer of energy through it (e.g. electrical).

Control rods

Absorb thermal neutrons to control the rate of reaction and maintain it at a steady rate.

Coolant

High specific heat capacity to take away heat energy from reactor.

Compression

Moving region in which the medium is more dense or of higher pressure than the surrounding.

Critical Angle (θ)

Angle of incidence at which from that point on, no more refraction will occur - only total internal reflection. Measured in degrees.

Critical Temperature

The temperature in which the electrical resistance of a material falls to zero.

Current (I)

Rate of flow of charge. Measured in amperes, A.

Couple

Two equal, opposite and parallel forces which create rotational force.

Charles' Law

A gas law

stating that the volume of a gas is directly proportional to the temperature of the gas, considering pressure remains constant.

Centripetal acceleration

Acceleration causing an object to move in a circular path, i.e. always acting towards the centre. Measured in ms-2

Centripetal force, Fc

The force responsible for an object moving in a circular path. Measured in Newtons.

c

Speed of light in a vacuum constant. ~ 3.00 x 108 ms-1

Displacement

The distance in a given direction.

Displacement (Oscillations)

Distance from equilibrium position. Measured in meters.

Diffraction

Property of a wave in which when it passes through a gap, it spreads out.

Density

Density is the mass of a body per unit volume

Drag

The resistive force on an object when it travels through a fluid.

Drift velocity (v)

The average velocity of electrons travelling within a material. Measured in ms-1

Ductility

The ability of a material to plastically deform under tensile forces without fracturing.

Doppler effect

The apparent shift in frequency of a wave caused by relative motion between the source and the observer.

Decay Constant

The probability of decay of a nucleus per unit time

Damping

A reduction in amplitude of an oscillation as a result of energy being drained from the system to overcome friction or other resistive forces.

Driving frequency

The frequency of the forced oscillation system.

Elastic energy (Ee)

Energy stored within an object due to an elastic change in its shape (i.e. stretch or compression). Measured in joules.

Elastic deformation

A change in objects shape in which it will return to its original shape once the force is removed.

Electrical energy

Energy of electrical charges due to their position in an electric field. Measured in joules.

Electric field strength (E)

The force per unit charge that a positive point charge would experience at a specified point in an electrical field. Measured in Volts per metre or Newtons per Coulomb

Electric potential (V)

The energy per unit charge that a positive point charge would require to move from infinity to a specified point in an electrical field.. Measured in Volts

Elementary Charge (e)

Amount of charge carried by a single proton or electron (1.6x10-19 C), which may be positive or negative.

Energy

The stored ability to do work

Electromagnetic Radiation

A form of progressive wave with perpendicularly oscillating magnetic and electric fields.

Electromotive Force (e.m.f)

Energy available to be transferred from other forms (e.g. chemical) into electrical, per unit charge.

Equilibrium position

The resting position for particles in a medium.

Equipotential Field Lines

Field lines that represent lines of equal electrical potentials. Perpendicular to electric field lines.

Extension (x)

The change in length of an object when a force is applied to it

Eccentricity

How 'squashed' an ellipse is. I.e. the closer the foci are, the less eccentric an ellipse is.

Escape Velocity

The minimum velocity of an object required to escape the gravitational field of a larger body.

Faraday's Law

The emf induced in a conductor is directly proportional to the rate at change of magnetic flux linkage.

Force

A force causes a mass to change motion.

Frictional Force

Force arising when two objects rub against each other.

Frequency

The number of oscillations per second. Measured in hertz, Hz.

Free oscillation

When a pendulum is pulled to one side and allowed to oscillate freely,

Forced oscillation

Periodic driver is applied to an oscillator.

Fundamental particle

Particle with no internal structure.

fuel rods and control rods

Bombardment with neutrons causes fission and the release of energy.

Gravitational Field Strength (g)

The force that a unit mass would experience at a specified point. ms-2 or Nkg-1

Gravitational Potential

The work done per unit mass to move and object from infinity to a specified point in a gravitational field. Measured in Jkg-1

Gravitational Potential Energy

the energy an object has due to its relative position in a gravitational field.

Found by mass x gravity (or gravitational field strength) x height or force per unit mass at a set point in a gravitational field.

Measured in joules.

Gravitational Constant, G

Constant ensuring direct proportionality in newtons laws of gravitation. ~ 6.67x10-11m3kg-1s-2

Geostationary orbit

An orbit with equal period to that of the Earth (i.e. equal angular velocity). The orbit must be above the equator and rotate in the same direction as the Earth.

Geosynchronous

An orbit with equal period to that of the Earth. Doesn't have to be above the equator.

Hardness

Ability of an object to resist surface scratching and pressure.

Half life

Average time it takes for the number of radioactive nuclei in a sample to half.

Hadron

Particle composed of quarks in which interacts via the strong force.

Heat

A form of energy transfer, also known as 'Thermal Energy'.

Hooke's Law

An approximation that states that the extension of a spring is in direct proportion with the load added to it as long as this load does not exceed the elastic limit.

Hubble's Law

The recessional velocity of a galaxy is almost directly proportional to the distance, d, from Earth. (V≈H0 d)

Homogenous

The universe is composed of the same thing.

Heat flux, q, (Heat flow density)

Rate at which thermal energy is transferred per unit area, per unit time.

Heat transfer coefficient, h

How well heat is conducted over a series of resistant mediums.