# List of O Level Physics Definitions In this post, I have included a list of O Level Physics definitions. Here, you will find the common terms that you will be asked to define in O Level Physics exams.

Definition questions for O Level Physics are usually worth 1 to 2 marks each. Although it’s just simply a regurgitation question, it’s a pain to many as such questions are just pure memorising, and in order to score, you’ll need to make sure you have the keywords in your answer. My advice for O Level students would be to keep this list with you, and memorise the definitions (or test how well you remember them) a few days before the exam.

In this post, you will find the common definitions asked for O Level Physics. Note that this is not an exhaustive list but should cover most of what you need (to define) for your exam.

## O Level Physics Definitions based on topics

I have classified all these terms that you need to define according to the topics. Click on the link below to go straight to the definitions in the particular topic.

### Definitions: Physical Quantities, Units and Measurement

Scalar Quantity: A scalar quantity is one that has magnitude but no direction. e.g. mass, time, distance, speed

Vector Quantity: A vector quantity is one that has both magnitude and direction. e.g. displacement, force, velocity, acceleration.

### Definitions: Kinematics

Speed: Speed is the rate of change of distance with time.

Velocity: Velocity is the rate of change of displacement with time.

Acceleration: Acceleration is the rate of change of velocity with time.

Constant acceleration: A body is moving at constant acceleration when there is a constant rate of change of velocity with time.

### Definitions: Dynamics

Newton’s First Law of Motion: Newton’s first law of motion states that every object will continue in its state of rest or uniform velocity if no net force acts on it.

Newton’s Second Law of Motion: Newton’s second law of motion states that for an object with a constant mass, the net force acting on it is directly proportional to its acceleration. The direction of the acceleration is the same as the direction of the net force.

Newton’s Third Law of motion: Newton’s third law of motion states that if an object A exerts a force on object B, then object B must exert of force of equal magnitude and in opposite direction back on object A.

Friction: Friction is the force that opposes motion. It only acts when an object is moving.

### Definitions: Mass, Weight and Density

Mass: Mass is a measure of the amount of substance in a body.

Weight: Weight is the amount of gravitation force acting on a body.

Inertia: Inertia is the state that mass of a body resists a change in the state of rest or motion.

Gravitational field: Gravitational field is a region in which a mass experiences a force due to gravitational attraction.

Gravitational field strength: The gravitational field strength at a point is the gravitational force acting per unit mass.

### Definitions: Turning Effect of Forces

Principle of moments: Principle of moments states that for a body to be at equilibrium, the sum of the clockwise moment about a point is equal to the sum of the anti- clockwise moment about the same point.

Moment: Moment of a force is equal to the product of the force and the perpendicular distance from the line of action of the force to the pivot.

### Definitions: Pressure

Pressure: Pressure is the force acting per unit area.

### Definitions: Work, Energy, Power

Principle of conservation of energy: Principle of conservation of energy states that energy cannot be created or destroyed. It can only be converted from one form to another, or transferred from one body to another. Total amount of energy in an isolated system is always constant.

Work done: Work done is the product of force and distance moved in the direction of the force.

Power: Power is the rate at which work is done.

Efficiency: Efficiency is the ratio of useful power output to total power input. OR Efficiency is the ratio of the energy converted to useful output to the total energy input.

### Definitions: Temperature

Temperature: Temperature is the measure of the degree of hotness or coldness of a body.

### Definitions: Transfer of Thermal Energy

Conduction: Conduction is a process where heat is transferred through a medium from one particle to another.

Convection: Convection is a process where heat is transferred by the movement of heated particles of a fluid.

### Definitions: Thermal Properties of Matter

Heat capacity: Heat capacity is the thermal energy needed to change the temperature of the entire substance by 1 degree Celsius.

Specific heat capacity: Specific heat capacity is the thermal energy needed to change the temperature of a unit mass of the substance by 1 degree Celsius.

Latent heat of fusion: Latent heat of fusion is the energy required to change the entire substance from solid to liquid without a change in temperature.

Specific latent heat of fusion: Specific Latent heat of fusion is the energy required to change a unit mass of the substance from solid to liquid without a change in temperature.

Latent heat of vaporisation: Latent heat of vaporisation is the energy required to change the entire substance from liquid to gas without a change in temperature.

Specific latent heat of vaporisation: Latent heat of vaporisation is the energy required to change a unit mass of the substance from liquid to gas without a change in temperature.

### Definitions: General Wave Properties

Speed: Speed of wave is the distance travelled by the wave over the time taken.

Frequency: Frequency of the wave is the number of oscillations per unit time made by a particle of a wave.

Wavelength: Wavelength is the distance between two successive points on a wave that are in phase.

Period: Period is the time taken for a particle of a wave to complete one oscillation.

Amplitude: Amplitude is the maximum displacement of a particle from its equilibrium position.

Wavefront: A wavefront is an imaginary line or curve that joins all adjacent points of the waves in the same phase.

### Definitions: Light

Refraction: Refraction is the bending of light rays as they pass from one optical medium to another and undergo a change in speed.

Refractive index: The refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in the medium.

Critical angle: Critical angle is the angle of incidence in the optically denser medium for which the angle of incidence in the optically less dense medium is 90o.

Total internal reflection: Total internal reflection occurs when light is travelling from an optically denser to an optically less dense medium and the angle of incidence in the denser medium is greater than critical angle.

Focal length for a converging lens: Focal length is defined as the distance from the optical centre of the lens to the focal point on the principal axis.

### Definitions: Electromagnetic Spectrum

Electromagnetic waves: Electromagnetic waves are transverse waves that travel with the same speed in
vacuum and state the magnitude of this speed.

### Definitions: Sound

Ultrasound: Ultrasound is sound that has a frequency greater than the higher limit of the human audible range i.e. 20000 Hz.

### Definitions: Static Electricity

Electric field: An electric field is a region in which an electric charge experiences a force

### Definitions: Electricity

Current: Current is the rate of flow of charges.

Electromotive force (e.m.f): Electromotive force (e.m.f.) is the work done by a source in driving unit charge around a
complete circuit.

Potential difference (p.d.): Potential difference (p.d.) across a component in a circuit is the work done to drive unit charge through the component.

Ohm’s Law: Ohm’s law states that the potential difference across a conductor is proportional to the electric current passing through it, provided that its temperature remains constant.

Fuse: A fuse is placed in the live wire so that if there is a fault in the circuit, and the current exceeds the fuse rating, the fuse melts, and stops the flow of current through the circuit.

Circuit breaker: A circuit breaker will open the circuit when the current exceeds a predetermined amount.

Double insulation: Double insulation consists of two layers of insulation to ensure the outer casing of an appliance does not become ‘live’

Live wire: A live wire is connected to the high voltage supply and allows current to flow through and reach the appliance.

Neutral wire: A neutral wire is connected to the 0 Volts supply and allows current to flow back to the source and hence completes the circuit.

Earth wire: An earth wire is a wire with a very low resistance. In the event the live wire touches the metal casing, causing the metal casing to become ‘live’, the earth wire conducts the current away to earth, preventing the user who touches the metal casing from getting an electric shock.

### Definitions: Magnetism, Electromagnetism and Electromagnetic induction

Magnetic field: A magnetic field is a region in which a magnetic material placed in that region experiences a magnetic force.

## Learn On-demand – O Level Physics Courses

Knowing the definition is only a small part of the O Level Physics exam. We go into detail what you need to know, and how to apply the concepts in our O Level Physics courses. Find out more here.