# Physics

This is for a IGCSE paper

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## Forces and Motions - Main Equations

Speed = Distance / Time OR s = d / t

Acceleration = change in speed / time OR a = (v-u)/t

Force = Mass / Acceleration OR f = m / a

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## Force and Motion - Graphs

On a distance time graphs if:

the line goes upwards it means it is moving forwards,

The line goes downwards you are going backwards

The line stays the same then the object is stationary.

On a speed time graph if:

The line goes up the object is accelerating

The line stays the same then the object is moving at a constant speed.

The line goes down then it is deccelerating.

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## Forces and Motion - Newton's Law

First Law:

A body will not accelerate unless acted upon by an external force.

Second Law:

The more mass the body has, more force must be exerted to move it.

Third Law:

If object A exerts a forc on object B then B will exert en equal force on A.

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## Forces and Motion - Terminal Velocity and Effector

Terminal Velocity is when a body travels at a constant speed because two forces are acting equally on eachother.

The effectors of stop a body is on the friction. Friction is a force that always acts to opposite motion.

Static Friction acts on staionary objects.

Dynamic Friction acts on moving objects.

Static Friction is greater than dynamic friction.

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## Electricity - Main Equations

Current = charge / time OR I = Q / t

Voltage = current x restistance OR V = IR

Power = current x voltage OR P = IV

Energy = power x time OR E = Pt OR E = IVt

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## Electricity - Voltage Current Graphs

On a Voltage Current Grpah:

• Wires go up at a constant speed because the resistance does not change.
• Bulbs the it goes straght up then flattens because the filament heats up, the atoms vibrate so the resistance increases.
• Diodes stay at the bottom the at 0.4 goes slightly up then at 0.6 it goes straight up because diodes turn on at 0.6V and they have infinite resistance before.
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## Electricity - Wiring a Plug

There are tree wires, The Earth Wire, The Live Wire and The Neutral Wire.

There is a fuse by the live wire and a cable grie where they are led through an outer insulator.

Fuses are used because if there is a fault, large currents go through to cause a fire. The fuse will melt the wire at 13A and will cut the circuit.

Cicuit Breakers are like fuses however they can reset by using an elctro magnet which will open the switch so no current can flow when it is over 13A.

The Earth Wire in a circuit connects to the Earth. If there is a fault the current can go through a human to get towards the Earth and a human can die from over 0.2A, the Earth wire is much less resistant therefore the current will go through the Earth wire.

A.C. (alternating current) gets the electrons to go backwards and forwards which is called ostrillation and transfers energy. D.C. (Directional Current) has a constant potential difference cause electrons to flow around a circuit.

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## Waves - Main Equations

Frequency = 1 / Time Period OR f = 1 / T

Wavespeed = Frequency / Wavelength v = f / upside down y

Refractive index = sin i (angle of incidence) / sin r (angle of reflection)

sin critical angle = 1 / n

Angle of incidence = Angle of Reflection

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## Waves - General

The two types of waves are:

Longitudinal where the particles vibrate parallel to the direction of the wave.

Transverse where particles vibrate perpendicular to the wave.

The amplitude is the maximum displacement of 0.

The frequency is the number of waves in a second.

The wavelength is the horizontal distance of one cycle.

Time period is the time taken for one cycle.

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## Waves - Refraction

Refraction is when a wave bends around an edge.

Maximum refraction occours when the egde is at a angle and the gap is the same size of the wavelength.

Total internal refraction occours when the angle of incidence is greater than the critical angle.

Optical fibres ________________________________________

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## Energy - Main Equations

Efficiency = (useful energy / total energy) x 100

Work Done = Energy

gravitation potential energy = mass x gravity x height OR g.p.e = mgh

Kinetic Energy = 1/2 x mass x (speed squared) OR k.e. = 1/2m(v squared)

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Hydroelectric damn produces no pollution, no fuel cost and lots of power generated. HOWEVER: Sediment build up blocks the damn, and the reservoir destroy wildlife and dislocates people.

Solar Energy is light free, no pollution or moving parts. HOWEVER: The sun does not always shine, not much electricity produced, expensive and inefficient.

Tide Power has no fuel cost, no pollution, lots of energy produced and very predictable. HOWEVER: They are expensive and environmentally destructive.

Wave Power has no fuel cost, no pollution and not expensive. HOWEVER: they are easily damaged through corrosion, difficult to maintain and unpredictable.

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## Density

density = mass / volume OR backwards g = M / V

The density of water = 1000 kg / m cubed.

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## Pressure

Pressure = force / area OR p = F / A

Pressure in a fluid = density x gravity x height or p = backwards g x g x h

Pressure acts equally in all directions and increases with the depth of the fluid.

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## Particles

In a solid particles are in a fixed lattice, they have strong bonds and vibrate about a fixed point.

Liquids are close together but no bonds, particles can flow past each other and they have a fixed volume but no fixed shape.

Gases are free to spread and have no fixed volume or shape.

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## Electromagnetism

A charged particle moving through a magnetic field will experience a force that wires experience. The size and direction of this force depends on:

1. The magnitude and size of the charge.          2. The strength of the magnetic field.          3. The speed at which the particles are moving.

Lorentz left hand rule is where you first finger shows you the direction of the field, the second finger shows you the direction of the current and the thumb shows you the motion.

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