Physics IGCSE Revision

Volume and Density

Density VolumeMass=

m= Vρ(rho)

Volume and DensityHow to find the volume of an irregular solid?• You need to fill up a measuring cylinder with

water and measure till where it is filled.• Then lower the irregular solid into the

measuring cylinder and measure how much the water has risen.

• Subtracting the two values that you have will give you the volume of the substance.

Speed

Speed Time

Distance=

Velocity

Average Acceleration Time

Taken

Change in velocity=

v-u= ta v= final velocityu=initial velocityNegative

acceleration is called deceleration or retardation

Forces• A force is a push or a pull.• Force is measure in Newton's (N).If no external forces are applied to an object:- It will remain stationary- It will keep moving at a constant speed.What is Terminal Velocity?It is when something is at its maximum speed.

Forces

Force AccelerationMass= xF am= x

Friction• Friction is a force that stops two materials from

sliding across each other.• Static Friction resists the lateral (sideways)

movement of two objects.• Dynamic Friction is the friction between two

objects that are moving. It heats up the material. When something is moved against the force of friction the kinetic energy is changed into thermal energy.

STATIC FRICTION IS GREATER THAN DYNAMIC FRICTION

Gravitational Force• All the masses attract each other.• The greater the mass, the greater the force.• The closer the mass, the greater the force.

• To every action there is an equal but opposite reaction.

Gravitational Force

Weight GravityMass= xW gm= x

The Parallelogram Rule

1. First you need to draw the two lines given to you. The directions should be accurate and the length of each line should be in proportion to the magnitude of each vector.2. Then draw in two more lines to complete the parallelogram.3. Diagonal from ‘O’ and then measure its length.

Centripetal Force• It is an inward force needed

to make an object move in a circle.

More centripetal force is needed if:

- Mass of the object is increased

- Speed of the object is increased

- Radius of the circle is increased.

MomentsMoment of

a force about a

point

Perpendicular distance from

the pivot

Force= x

The Principle of MomentsClockwise moments = Anticlockwise moments

Hooke’s LawA material obeys Hooke’s law if, beneath the elastic limit, the extension is proportional to

the load.

Load ExtensionSpring Constant

= x

F k= x

Pressure

Pressure Area

Force=

Pressure in Liquids• Its in all directions• It increases with depth• It depends on the density of the liquid• It doesn’t depend on the shape of the

container.Pressure GravityDensity= x x Height

pressure = x gρ(rho) x h

Hydraulic Jack*

Output Piston area=Input ForceOutput Force

Input Piston area

Pressure in Air• Pressure decreases as you rise through it.• It acts in all directions.Barometer: Measures atmospheric pressureManometer: Measures the pressure difference

Gas Law• When studying a gas, the following things should be

considered:a) Pressureb) Volumec) Temperature • Gas Law:

For a fixed mass of gas the pressure times the volume divided by the temperature is constant

PxV = ConstantT

EnergyWork Done

Distance moved in the direction

of the forceForce= x

W dF= x

Different Forms of Energy• Kinetic energy• Potential energy• Gravitational energy• Elastic energy• Chemical energy• Electrical energy• Nuclear energy• Thermal energy• Radiated energy

Energy• The law of conservation of energy

Energy cannot be made or destroyed, but it can change from one form to another.

Kinetic Energy = m½ v 2

Gravitational potential energy

= x gm x h

V = SpeedGain in kinetic energy is a loss in potential energy

Scalar and Vector Quantities Scalar: has magnitude

but no direction-Speed (magnitude of

velocity)- Time- Mass

Vector: has magnitudeand direction.

-Energy-Displacement-Velocity-Acceleration

Efficiency and Power

EfficiencyTotal energy

input

Useful Work done=

Power Time TakenWork done=

Useful Power Output

SpeedForce= x

Thermal Power StationsFuel burner

Nuclear reactorThermal Energy

Boiler

TurbinesGeneratorElectricity

Fuel Oxygen+ CarbonDioxide + Water + Thermal

Energy

Thermal Power Stations Problems• Increased rate of global warming• Sulphur dioxide causes acid rain• Transporting fuels could lead to pollution due

to leaks• Radioactive wastes are very dangerous• Nuclear accidents

Power Schemes1- Pumped storage scheme – wind farms2- Tidal power scheme3- Hydroelectric power scheme

Energy SourcesNon-renewableCoal, oil, natural gas- Supplies are limited- Carbon dioxide

concentration is increasing

Nuclear fuels- Expensive to build and

decommission

RenewableHydroelectric and tidal energy- Expensive to build- Few areas are suitable- May cause environmental damageWind energy- Large, remote, windy sites required- Noisy, ruin landscapeWave energy- Difficult to buildGeothermal energy- Deep drilling difficult and expensiveSolar energy- Sunshine varies- Solar cells difficult to transport

Thermal Effects• Solids-fixed volume and shape • Liquids-fixed volume but no fixed shape• Gases-no fixed shape and no fixed volume.

• Internal energy: total kinetic and potential energy of all atoms in a material.Objects as the same temperature have the same average kinetic energy per particle

Hotter material � faster the particles move� the more internal energy it has

Absolute Zero-273˚C= 0 Kelvin (0 K)

Kelvin Temperature/K = Celsius Temperature/˚C+273

This is the lowest temperature there is.It is a thermodynamic scale. It is based on the average kinetic energy of particles.

Thermal Effects• Thermal expansion: this is when a substance is

heated and its volume slightly increases.The pressure law:- When the Kelvin pressure doubles so does the pressure- Pressure ÷ Kelvin temperature � always has the same value

Thermal Conduction:Conduction is the process by which thermal energy is

transferred from the hot end to the cold end as the faster particles pass on their extra motion to particles along the bar.

Thermal Effects• More thermal energy is transferred if :- Temperature difference across the ends is

increased.- Cross-sectional area of the bar is increased- Length of the bar is reduced.

Convection

Hot air rises and cold air sinks ☺

Thermal Radiation• This is when things that absorb this radiation

are warmed up.

To increase the rate of evaporation- Increase the temperature- Increase the surface area- Reduce humidity- Blow air across the surface

Specific Heat Capacity

Energy Transferred = xSpecific

heat capacity

mass x Temp change

Energy Transferred

= x cm x ∆ t

Specific heat capacity is 4200J/K kg for water

Latent Heat of Fusion

Energy Transferred

mL=

Energy Transferred

Specific Latent HeatMass= x

Describing Waves Amplitude

Wavelength

Transverse Waves

• The oscillations are at right angles to the direction of the wave.

• For example light waves.

Longitudinal Wave

• It consists of compressions and rarefactions.• Oscillations are in direction of travel.• For example: Sound waves.

( Rarefactions)

The Wave Equation

Speed wavelengthFrequency= x

V f= x= Lambda

Wave Effects: Reflection

The waves are reflected from the

surface at the same angle they hit it.

Wave Effects: Refraction

Due to the plastic the water becomes

shallower causing the waves to slow down. This effect is called

refraction.

Plastic

Wave Effects: Diffraction

• Diffraction is when the light bends around obstacles.

• Wider gaps produce less defraction.

Sound waves• Sound waves are caused by vibration• Sound waves consist of Longitudinal waves.

- Compression passes� Air pressure increases-Rarefaction passes� Air pressure decreases

Sound Waves• Sound waves need a medium to travel in. For

instance the air.• Sound waves can also be diffracted due to their

long wavelength.• They can be displayed on an oscilloscope. The

sound enters via the microphone, a metal plate vibrates, these vibrations cause electrical oscillations producing a wave front.

IT IS NOT A PICTURE OF THE SOUND WAVE

BECAUSE SOUND WAVES ARE NOT

TRANSVERSE

Speed of Sound• Temperature of air: Sound travels faster

through hot air.• Does NOT depend on pressure: the pressure

may change but the speed of the wave will remain the same

• The speed of sound is different through different materials.

Ultrasound: sounds above the range of human hearing which is between 20Hz & 20kHz

How to Measure the speed of an echo?

You could use:- Echo-sounder- Electronic tape measure (Works like an echo-

sounder)- Radar

Speed Time

Distance=

To measure echoTake note here the distance is the distance from to the wall and then BACK !

Features of Light1. Form of radiation2. Travels in straight lines3. Transfers energy4. Transverse waves5. Can travel through vacuum6. 300,000 000 m/s

Law of reflection• i˚=r˚• i, r and normal lie on the same plane.

Total Internal Reflection

• Anything greater than the critical angle does not have a refracted ray. Which means that all the light is reflected thus leading to TOTAL internal reflection.

LensesConvex Lens Concave Lens

Convex lenses are used in projectors as they form large, inverted, real images on the screen

When the object is less than F1

Original ObjectRefracted Object Refracted image is

-Upright-Larger-Virtual

-It is also on the same side as F1

When the object is at 2F1

Refracted image is -At 2F2-Inverted-The same size-Real

When the Object is between F1 and 2F1

Refracted image is -Beyond 2F-Inverted-Larger-Real

When the object is beyond 2F1

Refracted image is -Between F2 and 2F2-Inverted-Smaller-Real

The Electromagnetic Spectrum

Electromagnetic waves are emitted when a charged particle oscillate or loose energy in some

way.

Electricity• Rubbing materials does not MAKE charge, it only

separates charges that are already there.• Induced charge: this is the charge that ‘appear’

on an uncharged object because of the charged object nearby.

Charge is measured in Coulombs.

Electricity*• Electrostatic precipitators: are fitted into

chimneys in order to reduce pollution

Electricity• When there are no ions in the air it is a good

electrical insulator.• When there are ions present in the air it is a

good conductor

Current is measured in amps.

Current• Current remains the same at all points round a

simple circuit.

Charge TimeCurrent= xConventional Current flows from positive to negative.Electron flow is from negative to positive.

Potential Difference (Voltage)• The highest potential difference is when it is

not in a circuit and it not supplying current. This is also known as the Electromotive force.

• In a simple circuit, the sum of the PD’s across the components is equal to the PD across the battery.

Resistance

ResistanceCurrent (A)

PD (Voltage)=

RIV

=Ohms Law

The current is proportional to the PD.

How can resistance be increased?1- Length : Doubling the length increases

resistance2- Cross-sectional area: halving the surface area.

(thin wire is more resistance than a thick one)3- Material4- Temperature: resistance increases with

temperature

CIRCUITSParallel Circuit

- Gets full PD from the battery- One bulb removed the other

still works- Total current = Sum of the

currents in the branches.- Resistance:

Series Circuits- Bulbs share PD- One bulb removed, the

other one goes out.- Current through each

component is the same- Resistance:

CIRCUITSParallel Circuit Series Circuits

Power

Power Time takenWork done=

Power

Power VoltageCurrent= x

P VI= x

Power

Power ResistanceCurrent= x

P RI= x

2

2

Electrical Energy Equation

Energy Transformed TimePD= xCurrentx

E tV= xIx

Brief Intro on MagnetsMagnetic material- is a type of material that can be magnetized and is attracted to other magnets.

Strong metals contain1- iron2- nickel3- cobalt

They are called “Ferromagnetics”

Iron and alloys of iron are called ferrous. (Ferrous in Latin means iron)Aluminium, copper, and other non-magnets are called non-ferrous.

Properties of magnets:• Have a magnetic field around them• Has two poles exerting forces on other

magnets.– Like poles repel– Unlike poles attract

• Attract magnetic materials by inducing magnetism in them.

What is induced magnetism?Some metals like iron and steel are attracted to other magnets because if there is a magnet near by, they themselves get magnetized. Magnetism is INDUCED in them.– When steel is pulled away from a magnet, it keeps its

induced magnetism causing it to become a permanent magnet.(hard magnet)

– When iron is pulled away from a magnet, it looses its induced magnetism meaning that iron was only a temporary magnet.(soft magnet)

Magnetic Effects of Current• When an electric current is passed through a

wire an magnetic field is produced. The features of this magnetic field are:– They are circles– Field is strongest close to the wire– Increasing current � increases strength of field.

Right-hand grip rule

Electromagnets• These are types of magnets that can be

switched on and off.

Iron core Coils

The strength of the magnetic field can be increased by:- Increasing the current.- Increasing the number of turns in the coil

Magnetic Relay

• When electricity is passed through the coil end wires, it induced a magnetic field in the iron ROD. This attracts the iron STRIP causing both metal contacts to touch.

Metal contacts.

Circuit BreakerCircuit breaker- it is an automatic switch cutting off the current within a circuit if it rises above a specified value.

- In the case on the left, the pull of the electromagnet has become so strong that it has attracted the soft iron armature. This causes the contacts to open and stop the current.

- If u press the reset button, the contacts close once again.

Magnetic force on the current• Copper is a non-

magnet � feels no force of the magnet

But..• If it has a current

passing through it, there will obviously be a force on the wire.

The wire moves ACROSS the field. It is not attracted to it.

Force is increased if:-Current is increased-Stronger magnet is used-Length of wire in field is increased.

Flemings Left Hand Rule

Electric motors

• A motor is made up from a coil of wire which is positioned between the two poles of the magnet.

• When the current flows through the coil, it creates a magnetic field. This magnetic field that is produced interacts with the magnetic field produced by the 2 permanent magnets.

• The combination of these two magnetic fields exert a force, pushing the wire at right angles to the permanent magnetic field.

An electric motor transfers electrical energy to kinetic energy.

Improve turning effect

Increasing Turning Effect• Increase the current• Use a stronger magnet• Increase the number of turns on the coil• Increase the area of the coil.

Electromagnetic Induction• A magnetic field can be used to produce

current.When the wire is moved across the magnetic field a small EMF(voltage) is created. This is called electromagnetic induction.“EMF is induced”

Induced EMF increased by:-Moving wire faster-Using stronger magnet-Increasing length of wire.

Induced CurrentsFleming’s right hand rule:

Difference between the left hand and the right hand rule:-When current causes motion� the left hand rule applies-When motion causes current� the right hand rule applies

Generators• The coil rotates• Magnetic fields are cut• EMF is generated• Causes current to flow• Coil rotates– upwards,

downwards, upwards causing the current to flow backwards, forwards, backwards.

Increasing EMF:- Increasing the number of

turns on coil- Increasing area of coil- Use stronger magnet- Rotate coil faster

Coils and Transformers• Moving magnet induces EMF• Magnetic field SAME effect.• Mutual induction: when coils are magnetically

linked so that changing current in one coil causes an induced EMF in the other.

Simple Transformer- Alternating current flows

through primary coil- This sets up an altering

magnetic field in the core.

- Coils of the secondary coil ‘cut’ the altering magnetic field thus inducing an alternating voltage in the output coil.Turns in output coil

=Input voltage

output voltage

Turns on input coil

Step-up and Step-down transformersStep-up: this is when the number of output coils is greater than the number of input coils which means that there will be a greater output voltage as opposed to input voltage.

Step-down: this is when the number of output coils is less than the number of input coils which means that there will be less output voltage as opposed to input voltage.

Power Through a Transformer

= x Output current

Output voltage

Input voltage x Input

current

Generator (Electric Motor):Current + Magnetic Field = Motion

Electromagnetic Induction:Magnetic Field + Motion = Current

Thermionic Emission

• Basically what happens in thermionic emission is that the tungsten filament is heated to 2000 degrees Celsius. Some electrons that are hot enough escape the surface of the white hot surface. These then pass through the vacuum and on the screen.

The Oscilloscope

• The Cathode Ray Oscilloscope uses (as mentioned on previous slide) an electron gun and the X and Y plates to adjust where the stream of electrons go.

• The X-Plates move the beam horizontally (Left or Right)• The Y-Plates move the beam vertically (Up or Down)

• The Y-plates are connected to a Y input terminal. These are connected to an AC supply.

Examples of things that use electron beams:- Television- X-ray tube

Atoms

Nuclear Radiation

Alpha�Alpha particles are made of 2 protons and 2 neutrons.�This means that they have a charge of +2, and a mass of 4.�Alpha particles are relatively slow and heavy. �They have a low penetrating power - you can stop them with just a sheet of paper.�Because they have a large charge, alpha particles ionize other atoms strongly

Beta•Beta particles have a charge of minus 1, and a mass of about 1/2000th of a proton. .•They are fast, and light. •Beta particles have a medium penetrating power - they are stopped by a sheet of aluminum•Beta particles ionize atoms that they pass, but not as strongly as alpha particles do.

Gamma•Gamma rays are waves, not particles. This means that they have no mass and no charge. •Gamma rays have a high penetrating power -it takes a thick sheet of metal such as lead, or concrete to reduce them significantly.•Gamma rays do not directly ionize other atoms•We don't find pure gamma sources - gamma rays are emitted alongside alpha or beta particles. Strictly speaking, gamma emission isn't 'radioactive decay' because it doesn't change the state of the nucleus, it just carries away some energy.

In a Magnetic Field

What is Background Radiation?• Background radiation comes from naturally

decaying substances such as soil, rocks, air, food and drink.

• It is detected by a Geiger Muller Tube

Radioactive decay- Alpha Decay

Radioactive decay- Beta Decay

Half-Life• This is the amount of time taken for the nuclei

of a radioactive substance to decay.

Nuclear Fusion

This does not take place on Earth so far. It is the process that powers the stars.

Nuclear Fission

What can Radioactivity be used for?1. Tracers2. Radiotherapy3. Testing for cracks4. Thickness monitoring5. Carbon Dating- after an organism dies the amount of

C-14 inside it begins to decay. It can be used to find out how old a substance is.

6. Dating Rocks

This is the physics syllabus Complete

Best of luck for your IGCSE exams

IMPORTANT:Come to school during study leave and ask your questions

EXTRANOT IN SYLLABUS

Important electronic components1. Resistors – keep currents + voltages at levels

desired by the electronic component2. Capacitor – store small amounts of electric

charge3. Diodes – allow the current to flow in only one

direction 4. Light-emittingg diodes (LED) – glow when a

small current is passed through them.

Continued…5. Transistors – used to amplify signals6. Integrated circuits(micro-chips)– contain complete circuits with :

a) Resistorsb) Transistorsc) Other components

7. Relays– electromagnetic switches.

Diodes• Can be used to change AC to DC �

Rectification• Lets forward parts of the AC through but

blocks the backwards part.• Forming a DC

Input Output1 resister

Potential Divider• A potential divider only delivers a portion of

the voltage.

Reed Switch• A reed switch is operated by a magnetic field.

Transistors as switches• It is a

semiconductor device made of silicon.

Emitter

Base

Collector

The NPN resistor

• In the diagram above there are actually two circuits put together as one. The first circuit is the one with the base and the emitter ( input circuit) and the second is the circuit with the collector and the emitter (output circuit).

1. Two input connections joined together� no current flow2. Input the base greater than 0.6V�lamp switches on3. 1000 ohm resister is present to protect the input to the resistor, allowing input to

be higher than 0.6V to 5V without harming transistor.4. Little current is needed in the input circuit.

b

e

c1000 ohms 6 V

Logic Gates