Physics Definitions and Concepts

Flashcards created from physics definitions and concepts to aid study for an upcoming exam.

Specific charge

The charge in coulombs divided by the mass in kilograms; also known as charge to mass ratio.

Isotope

An atom with a nucleus that has the same number of protons but a different number of neutrons.

Photo-electric effect

The emission of electrons from metal surfaces by incident light of an appropriate frequency.

Work function

The minimum energy required for an electron to escape from the surface of the metal.

Threshold frequency

The minimum frequency of a photon required to produce photoelectrons.

Electron volt

The energy given to an electron when it passes through a potential difference of 1 V.

Ionisation energy

The minimum energy required to remove an electron from an atom in its ground state.

Excitation energy

The energy required to move an electron from a lower energy level to a higher energy level.

Line spectra

The characteristic wavelengths of light produced by individual excited atoms.

Electric current

The number of coulombs of charge passing a point every second.

Potential difference

The work done per unit charge in moving charges from one point in the circuit to another.

Resistance

The ratio of the potential difference across a component to the current through it.

Ohmic conductor

A conductor where the ratio of potential difference to current remains constant.

Ohm's Law

The current through a component is proportional to the potential difference across it.

Critical temperature

The temperature at or below which the resistivity of a superconductor becomes zero.

Kirchoff’s first law

The sum of the currents into a junction is zero.

Kirchoff’s second law

In any closed loop, the sum of the EMF equals the sum of the potential difference.

EMF (Electromotive Force)

The total energy supplied per coulomb given to charges as they pass through the battery or cell.

Internal resistance

The resistance inside a battery, cell, or power supply.

Useful volts

The potential difference across the terminals of the power supply.

Lost volts

The potential difference across the internal resistance of the power supply.

Root mean square (RMS)

The square root of the mean of all the squares of the values.

Time base

The control on an oscilloscope that changes the time it takes for the beam to cross the screen horizontally.

Y-Gain

The control on an oscilloscope that changes the sensitivity of the vertical voltage scale.

Scalar

A physical quantity that has magnitude only.

Vector

A physical quantity that has both magnitude and direction.

Equilibrium

An object is in equilibrium when the resultant force and resultant torque on it are both zero.

Couple

Two equal and opposite forces separated by a distance producing rotational motion.

Moment/Torque

The turning force about a point, equal to the force multiplied by the perpendicular distance to the line of action.

Principle of moments

For an object in equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments.

Centre of mass

The point at which the whole mass of an object appears to act.

Displacement

The distance an object has moved in a specific direction.

Speed

Distance travelled per unit of time.

Velocity

Displacement per unit of time.

Acceleration

The change in velocity per unit of time.

Parabolic path

The path of a particle moving with a component of motion at right angles to a constant resultant force.

Newton's first law

An object remains at rest or moves with a constant velocity unless acted upon by a resultant external force.

Newton's second law

The acceleration of an object is proportional to the resultant force applied to it, for constant mass.

Newton's third law

For every action, there is an equal and opposite reaction.

Work

Work done equals force multiplied by distance moved in the direction of the force.

Power

Power equals work done divided by time.

Principle of conservation of energy

Energy cannot be created or destroyed; it can only be transformed from one form to another.

Hooke's law

The extension of a spring or material is proportional to the tensile force applied, up to the limit of proportionality.

Elastic limit

The maximum extent to which a material can be deformed and still return to its original shape.

Tensile stress

The force applied per unit area of a material.

Tensile strain

The extension divided by the original length of the material.

Plastic behaviour

A material that does not return to its original shape after the forces causing deformation are removed.

Fracture

When material breaks.

Brittleness

A characteristic of materials that do not undergo plastic deformation before breaking.

Young's modulus

The ratio of tensile stress to tensile strain.

Amplitude

The maximum displacement from the equilibrium position.

Frequency

The number of oscillations per second.

Wavelength

The distance between two consecutive particles in a wave that are in phase.

Wave speed

The speed of energy transfer through the medium.

Path difference

The extra distance one of the waves has to travel compared to another to reach a point.

Electromagnetic wave

A transverse wave consisting of changing electric and magnetic fields.

Polarised waves

Electromagnetic waves with an electric field vector in one plane only.

Un-polarised waves

Electromagnetic waves with an electric field vector in many directions.

Refractive index

The ratio of the speed of light in a vacuum to the speed of light in a substance.

Critical angle

The angle of incidence at which the angle of refraction is 90°.

Total internal reflection

Occurs when the angle of incidence exceeds the critical angle, reflecting all light within the substance.

Step index fibre

A fibre with a sudden change in refractive index between the core and cladding.

Stationary wave

Formed by two waves of the same frequency and similar amplitude travelling in opposite directions.

Node

A point on a stationary wave with zero amplitude.

Antinode

A point on a stationary wave with maximum amplitude.

Fundamental frequency

The lowest frequency capable of producing a stationary wave.

Coherence

Coherent waves have the same frequency and a constant phase relationship.

Fringe spacing

The distance between two consecutive maxima or minima in an interference pattern.

Impulse

The product of force and time.

Principle of conservation of momentum

In a collision, momentum is conserved provided no external forces are acting.

Elastic collision

A collision in which kinetic energy is conserved.

Inelastic collision

A collision in which kinetic energy is not conserved.

Explosion (explosive collision)

A collision where kinetic energy increases due to energy transfer from the explosion.

Centripetal force

The resultant force keeping an object in circular motion, directed towards the center.

Angular speed

The number of radians per second swept by a rotating object.

Simple harmonic motion (SHM)

Motion where acceleration is proportional and opposite to displacement from equilibrium.

Energy in SHM

The energy of the oscillator is proportional to the amplitude squared.

Free vibrations

Oscillations at the natural frequency of the oscillator.

Forced Vibrations

Oscillations at the frequency of the driver.

Resonance

Occurs when the driver's frequency matches the natural frequency of the driven system.

Phase relationship in resonance

The driver leads the driven by a phase angle of π/2 radians or a time of T/4 seconds.

Newton’s Law of gravitation

The gravitational force between two objects is proportional to the product of their masses and inversely proportional to the square of the separation distance.

Field

An area in space explaining the force one object applies on another without contact.

Gravitational field strength (g)

The force per unit mass at a point in the gravitational field.

Electric field strength (E)

The force per unit positive charge at a point in the electric field.

Gravitational potential at a point

The work done per unit mass in bringing a small test mass from infinity to that point in the field.

Electric potential at a point

The work done per unit positive charge in bringing a small test charge from infinity to that point.

Inverse square law

The strength of radial fields decreases with the square of the distance from the center.

Parabolic path

The path taken by a particle moving with a component of motion at right angles to a constant applied force.

Circular path

The path taken by a particle under constant force applied at right angles to its motion.

Capacitance

The charge stored per volt in a capacitor.

Time constant

The product of resistance and capacitance, measured in seconds.

Magnetic flux density (B)

A measure of the strength of the magnetic field, measured in Tesla.

Tesla

The magnetic field strength required to exert a force of 1 N on a 1 m long wire carrying 1 A current.

Magnetic flux (Φ)

The product of magnetic flux density and the area through which it passes.

Magnetic flux linkage (NΦ)

The amount of magnetic flux passing through a wire coil multiplied by the number of turns.

Fleming’s left hand rule

Expresses the relationship between force (thumb), current (second finger), and magnetic field (first finger).

Cyclotron

A device utilizing alternating electric fields and a uniform magnetic field to accelerate charged particles.

Faraday’s Law

The induced EMF in a conductor is proportional to the rate of change of magnetic flux.

Lenz’s Law

Induced current flows in a direction to oppose the change that produced it.