OCR A-Level Physics/Glossary of Terms
Definitions of keywords and terms that you will need to know.
- 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.
- 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).
- A device used to measure the electric current in a circuit. It is connected in series with the components.
- Amount of substance
- A SI quantity, measured in moles (mol).
- The SI unit for electric current.
- The maximum displacement of a wave from its rest/mean position (measured in metres).
- A point of maximum amplitude along a stationary wave caused by constructive interference.
- Braking Distance
- Distance travelled from the brakes being applied to the car stopping completely.
- 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
- Two equal, opposite and parallel forces which create rotational force.
- The distance in a given direction
- Density is the mass of a body per unit volume
- Decay Constant
- The probability of decay of a nucleus per unit time
- Electric field strength (E)
- The force that a unit charge would experience at a specified point. Measured in Volts per metre or Newtons per Coulomb
- Electric potential (V)
- The energy that a unit charge would have at a specified point. Measured in Volts
- The stored ability to do work
- Extension (x)
- The change in length of an object when a force is applied to it
- Faraday's Law
- The emf induced in a conductor is directly proportional to the rate at which the magnetic flux changes.
- A force causes a mass to change motion
- The number of waves that pass a fixed point in a unit of time
- Gravitational Field Strength (g)
- The force that a unit mass would experience at a specified point. Measured in metres per second per second or Newtons per kilogramme
- Gravitational Potential
- The energy that a unit mass would have at a specified point. Measured in Joules per kilogramme
- Gravitational Potential Energy
- the energy an object has due to its relative position above the ground. Found by mass x gravity (or gravitational field strength) x height
- or force per unit mass at a set point in a gravitational field
- is 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.
- Instantaneous acceleration
- acceleration at a specific time; slope of tangent to velocity- time graph.
- Instantaneous position
- position of an object at specific time.
- Instantaneous velocity
- slope of the tangent to position- time graph.
- Internal energy
- sum of potential energy and kinetic energy with random motion.
- The SI unit of work done, or energy. One joule is the work done when a force of one newton moves an object one metre.
- Kinetic Energy
- The energy an object possesses due to its motion, given by KE = 0.5 x mass x velocity²
- Lenz's Law
- An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original change in magnetic flux.
Magnetic flux is the product of magnetic flux density and the projection of area onto a surface at right angles to the magnetic field
- Unit in which force is measured. Symbol "N". One Newton is the force required to give a mass of 1kg an acceleration of 1ms^-2
Voltage is directly proportional to current as long as all other physical properties remain constant (V =IR)
- Period (T)
- The time taken for one complete oscillation. Denoted by 'T'. T=1/f
- The rate at which work is done.
- The load applied to an object per unit surface area.
- Potential difference
- The work done in moving a unit positive charge from one point to the other. The unit is volt.
- Q or q
- Often used as the symbol for charge in equations
- The property of a material that measures it resistance to electric current. It is defined as the resistance a wire of the material would have if it had a cross sectional area of one metre square and a length of one meter.
- A radian is the angle subtended at the centre of the circle when the arc length is equal in length to the radius.
- A quantity with magnitude but no direction.
- A scalar quantity, speed = distance / time
NB s can also mean displacement.
- Stopping Distance
- Stopping distance = Thinking distance + Braking distance
- thinking distance (distance traveled while reacting) = time taken to react X velocity
- braking distance (distance traveled while braking)
- Specific Heat Capacity
- The amount of heat energy required to raise the temperature of a substance per unit of mass by 1 degree, without going through a change in state.
- Specific Latent Heat
- The amount of heat energy required to change the state of 1 kg of the mass of a substance, without a change in temperature.
- The amount of heat energy required for a phase change of 1 kg of the mass of a substance from solid to liquid or from liquid to solid, without a change in temperature.
- The amount of heat energy required for a phase change of 1 kg of the mass of a substance from liquid to gas or from gas to liquid, without a change in temperature.
- A SI quantity, measured in kelvin (K).
- Tensile force
The forces being applied onto a material (usually a wire) on two opposite sides in order to stretch it. Both forces' values are the same as the tensile force value.
- Tensile stress
- The tensile force per unit cross-sectional area.
- Terminal Velocity
- maximum velocity a body can travel. When resistive forces = driving force, acceleration = 0, so it cannot travel any faster.
- An electrical component that changes its resistance depending on its temperature.
- Thinking distance
- The distance travelled from seeing the need to stop to applying the brakes.
- Threshold frequency
- The lowest frequency of electromagnetic radiation that will result in the emission of photoelectrons from a specified metal surface.
- A type of force due to an engine (usually forward force).
- Time interval (t)
- A SI quantity, measured in seconds (s).
- Torque / moment
- Moment = force x perpendicular distance from the pivot to the line of action of the force
- Torque = one of the forces x the distance between them
- Transverse Wave
- A progressive wave that transfers energy as a result of oscillations/vibrations.
- Triangle of forces
- If three forces are acting at a point that can be represented by the sides of a triange, the forces are in equilibrium.
- Turning forces
- More than one forces that if unbalanced will cause a rotation.
- Ultimate tensile strength
- The maximum tensile force that can be applied to an object before it breaks.
- Ultimate tensile stress
- The maximum stress that can be applied to an object before it breaks.
- A form of electromagnetic wave (wavelengths 10-9-3.7x10-7m). It may cause sun tanning. Usually classified into three categeries:UV-A, UV-B and UV-C.
- A force experienced due to the pressure difference of the fluid at the top and bottom of the immersed portion of the body.
- A quantity with magnitude and direction.
- The (instantaneous) rate of change of displacement with respect to time. Velocity is a vector.
- Velocity-time graph
- A motion graph which shows velocity against time for a given body.
- Volt (V)
- The unit of potential difference (p.d.) or electromotive force (e.m.f.)
- A device used to measure the potential difference across a component. It is connected in parallel across a component.
- A physical quantity representing how much 3D space an object occupies, measured in cubic metres(m3)
- The unit of power.
- power = energy / time
- Series of vibrations that transfer energy from one place to another.
- The smallest distance between one point of a wave and the identical point of the next wave, measured in metres (m).
- Wave-particle duality
- The theory which states that all objects can exhibit both wave and particle properties.
- The gravitational force acting on a body, measured in newtons (N).
weight=mass x gravitational force
- Work Done
- The energy transferred when an object is moved through a distance by a force. Can be calculated by multiplying the force involved by the distance moved in the direction of the force.
Alternatively, [work done = transfer of energy]. i.e., work is done when energy is transferred from one form to another. [OCR do not accept this definition if asked "Define work done by a force"]
- Work function energy (Φ)
- The minimum energy that is required for a material to release an electron, measured in joules(J).
- X rays
- A form of electromagnetic wave (wavelengths:10-12-10-7m). It is used in X-ray photography.
- Young's double slit experiment
- An experiment to demonstrate the wave nature of light via superposition and interference.
- Young Modulus
- Stress per unit Strain, units: Pascals or N/m2