GCE A Level Physics - Key Terms and Definitions

Systematic Error

Systematic Errors result in all readings or measurements being either always above or always below the true value by a fixed amount.

Random Errors

Random errors results in readings or measurements being scattered about a mean value. These errors have an equal probability of being positive or negative.

Accuracy

Degree of closeness of the mean value of measurements to the true value

Precision

Degree of agreement between repeated measurements of the same quantity

Distance

The total length of a path an object travels

Displacement

The distance moved in a specified direction from a reference point

Speed

The instantaneous speed of an object is defined as the rate of change of distance with respect to time.

Velocity

The instantaneous velocity of an object is defined as the rate of change of displacement with respect to time.

Average Speed

The total distance travelled over total time taken

Average Velocity

The change in displacement over total time taken

Acceleration

Rate of change of velocity with respect to time.

Average Acceleration

Change in velocity over time taken

Newton's First Law

A body continues in its state of rest or uniform motion in a straight line unless an external resultant force acts on it

Inertia

Inertia of a body is its reluctance to start moving, or to change its motion once it has started

Mass

Intrinsic property of a body which resists a change in motion

Weight

Force experienced by a mass in a gravitational field

Equillibrium

When a state of a body remains unchanged even though two or more forces are acting upon it (translational and rotational equilibrium)

Newton's Second Law

The rate of change of momentum of a body is proportional to the resultant force acting on it and occurs in the direction of the force.

Momentum (of a body)

Product of its mass and its velocity

Newton's Third Law

If Body A exerts a force on Body B, then Body B exerts an equal and opposite force on Body A.

Impulse

Defined as the product of a force F acting on an object and the time delta t for which the force acts.

Principle of Conservation of Momentum

When bodies in a system interact, the total momentum of the system remains constant, provided no net external force acts on it

Hooke's Law

Hooke's Law states that the extension of a body is proportional to the applied load if the limit of proportionality is not exceeded

Centre of Gravity

The centre of gravity of a body is the point at which its hold weight (or resultant of the distributed gravitational attraction on the body) appears to act through

Couple

A couple consists of a pair of equal and opposite forces whose lines of action do not coincide and which tend to produce rotation only

Torque of a Couple

Product of the magnitude of one of the forces and the perpendicular distance between the forces

Density

Mass per unit volume

Pressure

Force per unit area, where the force is acting at right angles to the area

Upthrust

Upthrust is the vertical upward force exerted on a body by a fluid when it is fully or partially submerged in the fluid due to the difference in fluid pressure

Archimedes Principle

The upthrust on a body in a fluid is equal to the weight of the fluid displaced by that body

Principle of Flotation

For an object floating in equilibrium, the upthrust is equal in magnitude and opposite in direction to the weight of the object

Principle of Moments

For a body to be in rotational equilibrium, the sum of all the clockwise moments about any axis must equal the sum of all the anticlockwise moments about the same axis

Moment

Moment about an axis is the product of the force and the perpendicular distance of the line of action of the force from the axis

Work Done

Work done by a constant force is the product of the force and the displacement in the direction of the force

Principle of Conservation of Energy

Energy cannot be created or destroyed. It can only be converted from one form to another

Elastic Potential Energy

Energy stored in objects which have had their shapes changed elastically

Power

Rate of Work Done / Energy Conversion with respect to time

Angular Displaecment

Angle an object makes with respect to a reference line

Angular velocity

Rate of change of its angular displacement with respect to time

Newton's Law of Gravitation

Two point masses attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Gravitational Field

Region of space in which a mass placed in that region experiences a gravitational force

Gravitational Field Strength

Gravitational force experienced per unit mass at a point in space

Gravitational Potential Energy

Work done by an external force in bringing a mass at a point in a gravitational field from infinity to that point

Gravitational Potential

Work done per unit mass by an external force in bringing a small test mass from infinity to that point / a point in the gravitational field.

Escape Velocity

Minimum speed needed for the object to just escape from the gravitational influence of a massive body.

Kepler's Third Law

Square of the period of revolution of the planets are directly proportional to the cubes of their mean distances from the sun

Satellite

Moon, planet or machine that orbits a planet or star

Geostationary Satellite

A geostationary satellite is one that remains at a fixed position as viewed from any location on the earth's surface

Simple Harmonic Motion

Simple Harmonic Motion

Motion of a particle about a fixed point such that its acceleration is proportional to its displacement from the fixed point, and is always directed towards the point

Angular Frequency

Rate of change of phase angle of the oscillation, equal to the product of 2pi and its frequency

Amplitude

Magnitude of the maximum displacement of the particle from its equilibrium position

Period

Time taken to complete 1 oscillation

Frequency

Number of oscillations per unit time

Free Oscillations

Occurs when an object oscillates with no resistive and driving forces acting on it, and its total energy and amplitude remain constant with time

Damping / Damped Oscillations

Process whereby energy is removed from an oscillating system

Forced Oscillations

Forced Oscillations are produced when a body is subjected to a periodic external driving force.

Resonance

Resonance occurs when a system responds at maximum amplitude to an external driving force, which occurs when the frequency of the driving force is equal to the natural frequency of the driven system

Phase Difference

Phase difference between two particles on a wave or two waves at a point is a measure of the fraction of a cycle in which one is ahead of the other

Phase Angle

Phase angle of a wave is an angle that gives a measure of the fraction of a cycle that has been completed by an oscillating particle or by a wave.

Wavefront

A line or surface joining points on a wave that are in phrase

Wavelength

The shortest distance between two consecutive points that are in phase.

Progressive Wave

A progressive wave transports energy from one point to another in the direction of wave propagation

In Phase

Particles of a wave are considered to be in phase when they execute the same motion at the same time

Out of Phase

Particles that show different stages of motion are out of phase with each other. They have a non-zero phase difference.

Anti-Phase

Particles in a wave are in anti-phase when they execute motions that are out of phase by pi radians. (Equal but opposite displacements, velocities and accelerations)

Wave Intensity

Intensity I of a wave is defined as the rate of transfer of energy per unit area normal to the direction of energy transfer of the wave.

Transverse Wave

A wave in which particles oscillate in a direction perpendicular to the direction of energy transfer

Longitudinal Wave

A wave in which particles oscillate in a direction parallel to the direction of energy transfer

Polarisation

Phenomenon whereby the oscillations of the wave particles in transverse waves are restricted to one direction only and this direction is perpendicular to the direction of energy transfer.

Malus' Law

Malus' Law states that the intensity of a beam of plane-polarized light after passing through a polarizer varies with the square of the cosine of the angle through which the polarizer is rotated from the position that gives maximum intensity

Principle of Superposition

When two or more waves of the same kind meet at a point in space, the resultant displacement at that point is equal to the vector sum of the displacements of the individual waves at that point.

Stationary Waves

A stationary wave is the result of the superposition of two progressive waves of the same type, frequency, amplitude and speed, travelling along the same line but in opposite directions

Antinode

An antinode is a point in a stationary wave where the amplitude is the maximum

Node

A node is a point in a stationary wave where the amplitude is zero

Diffraction

Diffraction is the bending of waves after passing through an aperture or round an obstacle.

Coherence

Waves are coherent or exhibit coherence when they have a constant phase difference

Interference

Interference is the superposition of two or more waves to give a resultant wave whose resultant amplitude is given by the principle of superposition

Constructive Interference

Occurs when two coherent waves arrive at the same point with a phase difference of zero to provide a maximum amplitude (Fixed amplitude, varying displacement)

Destructive Interference

Occurs when two coherent waves arrive at the same point with a phase difference of pi radians to provide a minimum amplitude

Path difference

The path difference between two waves is the difference in the distance that each wave travels from its source to the point where they meet.

Huygen's Principle

All points on a wavefront could be regarded as secondary sources giving rise to their own outward spreading of circular wavelets. The envelop of wavefronts produced by secondary sources gives the new position of the original wavelet.

Rayleigh's Criterion

Rayleigh's Criterion states that two images are just resolved by an aperture when the central maximum of the diffraction pattern of one image falls on the first minima of the diffraction pattern of the other image.

Thermal Equilibrium

When there is no net flow of heat between two objects in thermal contact, the two objects are in a state of thermal equilibrium

Zeroth Law of Thermodynamics

If objects A and B are each separately in thermal equilibrium with object C, then A and B are also in thermal equilibrium with each other.

Thermometric Property

Physical property of a substance that varies with temperature

Thermodynamic Scale

The absolute scale of temperature or the thermodynamic scale of temperature is one that is independent of the property of any substance and has an absolute zero

Absolute zero

Zero point of the thermodynamic temperature scale and the temperature at which all substances have a minimum internal energy

Ideal Gas

A gas which obeys the equation of state pV=nRT at all pressures, volumes and temperature.

Specific Heat Capacity

Quantity of heat required per unit mass to cause a unit rise in temperature of the body

Specific Latent Heat of Fusion

Quantity of heat required to convert unit mass of solid to liquid without any change of temperature

Specific Latent Heat of Vaporization

Quantity of heat required to convert unit mass of liquid to gas without any change in temperature

Internal Energy

The internal energy of a system is the sum of the microscopic kinetic energy, due to the random motion of the molecules, and the microscopic potential energy, associated with the intermolecular forces of the system.

First law of Thermodynamics

The First Law of Thermodynamics states that the increase in Internal Energy of a System is equal to the sum of the heat supplied to the system and the work done on the system, and the internal energy of a system depends only on its state.

Cyclic Process

A cyclic process is one in which the system goes through a series of process and ends at its initial state

Electric Field

An electric field is a region of space in which a charge placed in that region experiences an electric force.

Electric Field Strength

The electric field strength at a point is defined as the electric force exerted per unit positive charge placed at that point

Coulomb's Law

Coulomb's Law states that the force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance between them

Electric Potential Energy

The electric potential energy of a charge at a point in an electric field is defined as the work done by an external force in bringing the charge from infinity to that point

Field of Force

Region of space in which another body carrying that property experiences a force when it is placed in the field