# IGCSE Definitions

This document contains the common definitions that may be asked in the Cambridge IGCSE examinations.

IGCSE Definitions

## IGCSE Definition List (2016)

### General Physics

Speed

Speed is the distance travelled by an object per unit time.

Acceleration

Acceleration is the rate of change of an object’s velocity.

Resultant force

Resultant force is the single force that has the same effect as two or more forces.

Weight

Weight is the product of the mass and the acceleration of free fall.

Density

Density is mass per unit volume.

Force

Force is the product of the mass and the acceleration of the body.

Newton

Newton the is the force required to give a mass of 1 kg an acceleration of 1 m s–2.

Momentum

Momentum is the product of the mass and the velocity of the body.

Impulse

Impulse is the change in momentum of a body.

Principle of conservation of momentum

The principle of conservation of momentum states that the total momentum before a collision equals to the total momentum after the collision.

Conditions for equilibrium

For an object to be in equilibrium, it must satisfy two conditions:

• there is no net forces on the body, AND
• there is no net moment on the body.

Moment of a force

The moment of a force is the product of the force and the perpendicular distance from the pivot to the force.

Principle of moment

The principle of moment states that for an object to be in equilibrium, the total clockwise moments about a point is the same as the total anticlockwise moments about the same point.

Hooke’s Law

Hooke’s law states that the extension of a spring is proportional to the load applied to it,

Pressure

Pressure is the force acting per unit area at right angles to a surface.

Pascal

Pascal is the SI unit of pressure, equivalent to one newton of force per square metre.

Principle of conservation of energy

In any energy conversion, the total amount of energy before and after the conversion is constant.

Efficiency

The efficiency of an energy conversion is the fraction of the energy that ends up in the desired form.

Work done

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

Joule

One joule of energy os the energy transferred by a force of 1 newton when it moves through a distance of 1 m.

Power

Power is the rate at which energy is transferred.

Watt

Watt is the power when 1 J of work is done in 1 s.

### Thermal Physics

Specific heat capacity

Specific heat capacity is the energy required per kilogram and per degree Celsius to raise the temperature of a substance.

Specific latent heat of vaporisation

Specific latent heat of vaporisation is the energy per kilogram required to cause a substance to change state from liquid to gas at its boiling point.

Specific latent heat of fusion

Specific latent heat of fusion is the energy per kilogram required to cause a substance to change state from solid to liquid at its melting point.

### Physics of Waves

Law of reflection

Law of reflection states that in a reflection, the angle of incidence equals to the angle of reflection.

Refractive index

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

Snell’s law

Snell’s law states that when a wave travels from vacuum to the medium, the refractive index of the medium is the ratio of sine of the incidence angle to the sine of the refraction angle.

Total Internal Reflection

Total internal reflection occurs at a boundary when a light travels with an angle of incidence greater than the critical angle from a denser to a less dense medium.

Real Image

A real image is an image which light falls on it and it can be formed on a screen.

Virtual Image

A virtual image is an image which light does not fall on it and it cannot be formed on a screen.

Frequency

Frequency is the number of waves per second passing a point.

Wavelength

Wavelength is the distance between adjacent crests of a wave.

Longitudinal waves

A longitudinal wave is a wave which the particles move back and forth parallel to the direction of the wave velocity.

Transverse waves

A transverse wave is a wave which the particles move back and forth perpendicular to the direction of the wave velocity.

Amplitude

The amplitude of a wave is the maximum distance that the surface of the wave is displaced.

### Electricity and Magnetism

Current

Current is the rate at which electric charge passes a point in a circuit.

Resistance

Resistance is the ratio of the potential difference across a resistor to the current flowing through it.

Electromotive force

Electromotive force is the amount of energy needed to push one coulomb charge round a circuit.

Potential difference

Potential difference is the amount of energy released from a resistor when one coulomb charge passes through it.

Volt(unit)

One volt is the SI unit of potential difference when 1 joule of energy is produced when 1 C charge passes through a point.

Transducers

An input transducer produces a voltage due to a change in the environmental conditions.

Law of magnetism

Like poles repel, unlike poles attract.

Light-dependent resistor

LDR is a resistor which the resistance depends on the intensity of light.

Thermistor

Thermistor is a resistor which the resistance depends on its temperature.

Diode

Diode is a component that allows current to flow in one direction only.

Logic gate

A logic gate is a device that receives one or more electrical input signals, and produces an output signal that depends on those input signals.

AND

OR

NOT

NAND

NOR

### Atomic physics

Alpha particle

Alpha particle is a helium nuclei and it has 2 protons and 2 neutrons.

Beta particle

Beta particle is a fast moving electron.

Gamma ray

Gamma ray is part of the family of electromagnetic waves.