IGCSE Physics notes

Physics

Moment of a force:

Moment of a force = force

x

Law of moments:

When a body is in equilibrium the sum of the clockwise moments about any point equals the sum of the anticlockwise moments

about the same point.

Centre of mass:

I. Centre of mass is the point where whole mass of the body assumes to be concentrated.

II. If the vertical line through the centre of mass is outside the base it will be a topples but if it’s passed through the base it will be

stable.

The stability of the body is increased by: 1. Lowering its centre of mass.

Energy measurement:

Work is set to be done when a force is applied at an object and the object is moved in the direction of the force.

Kinetic energy:

All moving objects have kinetic energy. ( )

Potential energy:

The energy due to change in position, shape, or state.

Power:

It’s the rate at which it transfers energy from one form to another. Efficiency:

Pressure: Speed Velocity Acceleration

Uniform acceleration ( ) Vsecond speed Ufirst speed Sdistance

The heat equation

Specific heat capacity:

The specific heat capacity of a substance is the heat required to produce a rise in 1 Kg

Specific heat capacity of water

( ) ( ) ( )

Thermal capacity:

It’s the quantity of heat needed to raise the temperature of the whole body by .

Specific latent heat of fusion:

The specific latent heat of fusion of a substance is the quantity of heat needed to change unit mass from solid to liquid without

Specific latent heat of fusion

Specific latent heat of vaporization:

The specific latent heat of vaporization of a substance is the quantity of heat needed to change unit mass from liquid to vapor

without change of temperature.

Specific latent heat of vaporization

Heat supplied by a heater:

Speed of wave

Circular motion:

The Ampere and the Coulomb

The unit of current is the Ampere (A) which is defined using the magnetic effect.

The unit of charge, the Coulomb (C)

The Coulomb is the charge passing any point in a circuit when a steady current of 1 ampere flows for 1 second,

( ) ( ) ( ) Series and parallel circuit

The current is the same at all points in a series circuit The current is different in the branches of a parallel circuit

Direct and alternating current

In a Direct current (d.c) the electrons flow in one direction only. In an Alternating current (a.c) the direction of flow reverses

regularly.

Voltages round a circuit

In series: The voltages at the terminals of a battery equal the sum of the voltages across the devices in the external circuit from one

battery terminal to the other.

In parallel: the voltages across devices in parallel in a circuit are equals.

V

The opposition if a conductor to a current is called its resistance. The resistance of a wire of a certain material:

i) Increases as its length increases

ii) Increases as its cross-section area decreases iii) Depends on the material

The Ohm

The ohm is the resistance of a conductor in which the current is 1 ampere when a voltage of 1 volt is applied across it.

Resistors in series:

. Also, if R is the combined resistance, and so

Dividing both sides by I, Resistors in parallel

Also, if R is the combined resistance, and so

For simpler case of two resistors in parallel

Inverting both sides,

Capacitor

It stores electric charge and is useful in many electronic circuits. Effects of capacitors in d.c and a.c circuits

The capacitor block d.c The capacitor passes a.c

Electric power Electronic system

Any electronic system consists of three parts: i) An input sensor or transducer

iii) An output transducer

A transducer is a device to convert a non-electrical input into an electrical signal or vice versa.

The processor decides on what action to take on the electrical signal receives from the input sensor;

The output transducer converts the electrical energy supplied by the processor into another form.

Light dependent resistor (LDR)

It’s a type if variable resistor where resistance depends in the amount of light falling on it. It is used in circuits to detect the level

of light

Dark high resistance less current Light low resistance more current

Thermistor

It’s a type of variable resistor where resistance depends on the temperature.

Cold high resistance less current Hot low resistance more current

Relays

Diode

It’s a component that allows the electric current to flow in one direction only. It’s also known as Rectifier. It changes alternative

current to direct current.

Magnetization of iron and steel

Magnetic materials like IRON which magnetize easily but readily lose their magnetism (are easily demagnetized) are said to be

SOFT.

But those like STEEL which are harder to magnetize than iron but stay magnetized are HARD.

Simple d.c electric motor

A direct current (DC) motor is a fairly simple electric motor that uses electricity and a magnetic field to produce torque, which turns

the motor.

Parts of the Motor

 DC power supply of some sort  Armature or rotor

 Commutator  Brushes

Lenz’s law

An induced current is always in such a direction as to oppose the motion or change causing it

Sensitivity of a thermometer

It is the length of increase of the liquid per degree rise in temperature. More sensitive means more noticeable expansion.

Linear scale

When the fixed points of the thermometer have been marked, the distance between them is divided into equal degrees which are the

range of the thermometer. Range of thermometer

The temperature limits of the thermometer. The lower limit and the upper limit.

Linear expansivity

The expansion can be calculated if: i) The length of the bridge,

ii) The range of temperature it will experience, and

iii) The linear expansivity of the material to be used, Are all known

Weight

Mass

Mass is the amount of matter in an object and is measured in Kg.

Hooke’s law:

Within elastic limit, the force is directly proportional to the extension produced.

Plastic

If a force is applied to an abject, the object changes its shape, and it stays the same shape when the force if removed.

Elastic

If you put a force on an object making the object change shape and it returns to its original shape after removing the force. We say the

object is Elastic.

Conditions of equilibrium:

I. The sum of the forced in one direction equals the sum of the forces in the opposite direction

II. The law of moments must apply.

Stable equilibrium

The body is in stable equilibrium when it slightly displaced and then released, it returns to its previous position.

Unstable equilibrium

A body is in unstable equilibrium if moves farther away from its previous position when slightly displaced and then released.

Neutral equilibrium

A body is in neutral equilibrium if it stays in its new position when displayed.

The gas laws Boyle’s law:

The pressure of fixed mass of gas is inversely proportional to its volume if its temperature is kept constant.

Charles’ law:

The volume of a fixed mass of a gas is directly proportional to its absolute temperature if the pressure is kept constant.

Pressure law:

The pressure of a fixed mass of a gas is directly proportional to its absolute temperature if the volume is kept constant.