Physics

Section 1 - Forces and Motion

average speed = distance moved / time taken

acceleration = change in velocity / time taken

Force - a push or pull of one body on another.

Examples of forces are:

• Applied force - transferred from a person or object to another. e.g. a man pushing a door.
• Gravitational force - a force caused by the attraction between objects by gravity.
• Normal force - when an object is in contact with another. e.g. a cup on a table.
• Friction force - when an object moves across a surface. e.g. a car driving.
• Air resistance - when an object travels through the air. e.g. a plane flying.
• Tension force - when an object is pulled in opposite directions.
• Spring force - when a compressed or stretched spring returns to its inert state.
• Electrical force - an attraction between oppositely charged objects.
• Magnetic force - an attraction caused by magnets.
• Upthrust force - buoyancy. e.g. the lift on a plane.

Vectors - something with both magnitude and direction. e.g. velocity, displacement.

F = MA

force = mass * acceleration 

W = MG

weight = mass * gravitational strength

p = Mv

momentum = mass * velocity

force felt = change in momentum / time taken

Airbags and such increase the time it takes for momentum to reach 0, thereby reducing the force felt.

Centre of mass - the point through which the weight of an object always acts through. 

Stability:

• Stable - the centre of gravity rises and returns to its equilibrium position. e.g. A ball in a bowl.
• Unstable - the centre of gravity falls and moves away from its equilibrium position. e.g. A ball in an inverted bowl.
• Neutral - the centre of gravity remains on the same level. e.g. a ball on a flat plane.

Moments:

Moment = force * perpendicular distance from the pivot

Taking the moment around ‘a’:

The anticlockwise moment = B * 10

The clockwise moment = 200,000 * 5 + 500 * 3

Therefore 10B = 1,001,500Nm

B = 100,150N

A + B = 200,500N

A = 100,350N

Taking the moment around ‘b’:

The clockwise moment =  A * 10

The anticlockwise moment = 200,000 * 5 + 500 * 7

Therefore 10A = 1,003,500Nm

A = 100,350N

A + B = 200,000 + 500

B = 100,150N

You can also take the moment around ‘c’:

Anticlockwise moment = B * (x + 10) + A * x

Clockwise moment = 200,000 * (x + 5) + 500 * (x + 3)

Therefore Ax + 10B + Bx = 1,001,500 + 200,500x

(A + B)x + 10B = 1,001,500 + 200,500x

(A + B - 200,500)x + 10B = 1,001,500

A + B = 200,500N

(0)x + 10B = 1,001,500

B = 100,150N

A = 100,350N

This proves that no matter where you take the moment from the result is always the same.

Stretching materials:

Hooke’s Law - the deformation of a body is directly proportional to the force applied to it, provided that the limit of proportionality is not exceeded.

This is translated into the formula F = kx where F is the force applied, x the extension of the spring and k the spring constant.

The limit of proportionality is the point at which the force and the extension of the spring are no longer proportional.

The elastic limit is the point at which the spring will not return to its original length when the force is removed. 

Elastic behaviour - materials are said to be elastic if they can regain their original size and shape.

Plastic behaviour - materials are said to be plastic if they do not return to their original size and  shape.

Section 2 - Electricity 

V = I * R

voltage = current * resistance

p = I * V

power = current * voltage

e = I * V * t

energy transferred = current * voltage * time taken

I = Q * t

current = charge * time taken

V = J / Q

voltage = joules / charge

mains supply = AC (alternating current) whereby the current is inverted very rapidly.

cell/battery = DC (direct current) whereby the current is always in one direction.

RMS (root mean square) = is a way to convert from peak voltage to shown voltage. The equation is:

RMS = peak AC voltage / √2

The following three graphs show the relationship between current and voltage.

As the voltage on a resistor increases, the current increases directly proportional to the voltage.

As the voltage on a filament lamp increases, the current increases but decelerates. This is because as current increases so does heat, the extra heat causes the atoms in the filament lamp to vibrate more, this creates more resistance thereby meaning less current can pass.

The current of a diode only increases when a certain set amount of voltage has been reached. After this point, current increases directly proportional to voltage. 

Benefits of series and parallel circuits :

Series:

• Energy efficient
• Less wiring

Parallel:

• Practical (can be independently controlled)
• If one part of the circuit was to break the entire circuit would not.
• Each closed loop would always receive the same amount of voltage so if for example, a lamp was added in parallel, all the lamps would remain bright while in a series circuit it would dim.

LDR = as light decreases so does the resistance

Thermistor = as heat decreases so does the resistance

The mains supply is 230V (RMS) with a peak voltage of 325V. Because of this, it is very dangerous if the mains charge is transferred to humans. Therefore, mains plugs have many safety features.

Safety features of mains plugs:

1. The body is made of plastic, a good insulator.
2. There is an earth pin to stop the plug from becoming charged. The earth pin is longer than the others so that it is always the first to make and the last to be broken.
3. The cable is clamped to stop the wire from being pulled out.
4. When there is no earth pin double insulation is used. This is where a layer of non-conductive material is wrapped around the body to stop it becoming charged.
5. A fuse is placed on the live wire. When there is high current, enough temperature is created to melt the fuse, which breaks the circuit causing it to stop working.

Mains plugs wire colours:

• live - brown
• neutral - blue
• earth - green and yellow

Waves:

Properties of waves:

Transverse waves - One which the vibrations are perpendicular to the direction of travel of the wave. e.g. a slinky jerked sideways, rope, water, the electromagnetic spectrum.

Longitudinal waves - One which the vibrations are parallel to the direction of the wave. e.g. sound waves, slinky jerked along its length. 

Time period = time / number of waves in that time

Frequency = 1 / time period

Wave velocity = frequency * wavelength

Waves transfer energy and information without movement of matter.

Wave behaviour:

Reflection - this is where a wave hits a surface and bounces back. The angle of incidence (angle at which the wave hits the surface) must be the same as the angle of reflection (the angle at which it  bounces back)

Refraction - this occurs as wavelength decreases when a wave goes from a less dense to a denser material. The light bends to the normal or away if from a dense to rare material. The way to calculate the angle of refraction is through the formula:

n₁ * sini = n₂ * sinr

where n = refractive index (speed of light / speed in material)

Diffraction - when waves move past an obstacle or through a gap it spreads out. This is called diffraction. Diffraction is largest when the gap is the same size as the wavelength.

The Electro-Magnetic Spectrum:

In order of increasing frequency and decreasing wavelength:

radio waves —> microwaves —> infrared —> light —> ultraviolet —> X-ray —> gamma rays

Uses:

• Radio waves - used in broadcasting and communications. Also used to transmit radio and TV.
• Microwaves - used in cooking and satellite transmissions.
• Infrared - used in heaters, optical fibre communication, remote controls and light vision.
• Light - used in optical fibres and photography.
• Ultraviolet - used in sunbeams, fluorescent lights, and security coding of bank notes.
• X-ray - used to produce internal structures of objects and materials. Used in medicine and security.
• Gamma rays - used for sterilisation and killing cancer cells.

Dangers:

• Microwaves - can cause internal heating of body tissue.
• Infrared - causes burning of skin if under the presence for too long.
• Ultraviolet - causes changes to surface cells, blindness and skin cancer.
• Gamma rays and X-ray - changes the DNA of cells and causes cancer and mutations.

Light:

Light waves are transverse waves that can be reflected, refracted and diffracted.

Examiners often like to ask for a part of the ray diagram to be drawn, drawing it similar to this will get you full marks on that question.

In an exam, the paper may ask to work out the real or apparent depth of an object in water, here is the formula to work it out:

real depth / apparent depth = n (the refractive index of the dense material)

Measuring the refractive index of glass:

1. Place a glass block on paper and draw around it.
2. Mark the normal and draw a few different angles of incidence.
3. Send the light rays along the angle and draw the emerging rays from the block.
4. Connect the ray and measure the angle of refraction.
5. Draw a graph of sini and sinr with sini on the y-axis and sing on the x-axis.
6. The gradient of the graph will be the refractive index.

Critical angle - the angle of incidence where the refractive angle is 90º. The equation to work it out is:

n₁ * sinc = n₂

Where n₁ is the refractive index of the denser material, c the critical angle, and n₂ is the refractive index of the rarer material.

Total Internal Reflection - this occurs when the angle of incidence is large than the critical angle when this happens the light reflects and does not refract. This principle is used in bike reflectors and fibre optic cables which are used in communication and endoscopy.

Sound:

Sound waves are longitudinal waves that can be reflected, refracted and diffracted.

Sound waves move through the vibrations of particles in the air. These vibrations are carried. However, although energy is transferred, matter is not.

The human range of hearing is 20Hz to 20,000Hz.

The Speed of sound is around 340m/s in air. This can be tested by performing the following experiment:

1. Measure the distance between 2 places.
2. Have a sound be made at one end.
3. As soon as the sound is made start a stopwatch.
4. When you hear it return stop the stopwatch.
5. The distance the sound travels divided by the time taken will give the speed.

Sound waves can be displayed by using a microphone to detect sounds and then feeding the information gained from it into an oscilloscope which displays the sound wave.

Pitch is controlled by the frequency of the sound wave.

Loudness is controlled by the amplitude of the sound wave.

Analogue and Digital:

Analogue - varies continuously in amplitude

Digital - only two different states exist - on or off

Advantages of digital:

• Less likely to be corrupted by noise as it is harder for the data to be changed by noise since it can only be either 1 or 0.
• Can be restored to its original form relatively simply.
• No loss of quality in amplification while in analogue signals it is very easy for noise to also be amplified therefore decreasing the quality.
• Can be stored in small memory and is processed very quickly by processors.
• More information can be carried by multiplexing.

Section 4 - Energy resources and transfer:

Examples of energy transfer:

• Chemical energy (in food) —> Kinetic energy (in muscles)
• Electrical energy (in circuits) —> Heat energy (from heat leakage from excess current)
• Kinetic energy (in muscles) —> Sound energy (from voice box)
• Elastic potential energy (in taught string) —> Kinetic energy (when string is relaxed)
• Chemical energy (battery) —> Light energy (from phone screen)

Energy is never lost but transferred, this is the principle of conservation of energy.

Energy Efficiency:

Energy efficiency = useful energy output / total energy input

The energy efficiency can be shown by using a Sankey diagram as below: 

The above Sankey diagram shows a light bulb. Its energy efficiency is 0.1 as it loses most of its energy through heat.

Energy can be transferred through conduction (transferred through touch), radiation (infrared) and convection whereby particles with energy rise allowing others to fill the space. If the source of energy continues the convection will continue and repeat. Convection is responsible for the distribution of heat energy. An insulator is bad at conducting so insulating buildings will stop heat energy from conducting away.

W = f * d

work done = force * distance moved in the direction of the force

Work done is also equal to energy transferred.

GPE = m * g * h

gravitational potential energy = mass * gravity field strength * height

KE = 0.5 * m * v²

kinetic energy = 0.5 * mass * velocity * velocity

p = W / t

power = work done / time taken

Energy production:

The following three methods all use natural processes to generate energy. The advantage with this is that it is green and renewable. However, they produce generally less energy and also cause visual pollution 

• wind —> turns turbine —> runs generator —> creates electrical energy
• water —> turns turbine —> runs generator —> creates electrical energy
• geothermal reserves —> heats water to make steam —> turns turbine —> runs generator —> creates electrical energy

The next two methods also use natural processes. However, these two rely on the weather. They again produce relatively less energy and can cause visual pollution 

• solar heating system —> heats water to make steam —> turns turbine —> runs generator —> creates electrical energy
• solar cells —> converter changes sunlight into electricity—> creates electrical energy

The next is probably the most common method of production energy. However, it causes pollution and is non-renewable. It does produce relatively more energy, though.

• fossil fuels —> heats water to make steam —> turns turbine —> runs generator —> creates electrical energy

This final one is probably the most dangerous method and produces toxic nuclear waste. However, it produces large amounts of energy and is technically renewable.

• uranium —> nuclear fission —> heats water to make steam —> turns turbine —> runs generator —> creates electrical energy

Section 5 - Solids, Liquids, and Gases:

This is one of the simplest sections. As such there is only a small amount of information that you need to know.

p = m / v

density = mass / volume

p  = F / A

pressure = force / area

The pressure at a point in gas or liquid at rest acts equally in all directions.

p = h * p * g

pressure difference = height * density * gravitational field strength

Particles within a liquid have random motion within a closely packed irregular structure.

Particles within a solid vibrate about a fixed position within a closely packed regular structure.

Brownian Motion - this is the principle that particles move randomly about a space and that when particles collide they exert a pressure on a surface.

Kelvin:

We are all familiar with the celsius and Fahrenheit scales which are used to measure temperature. In science, another scale called the kelvin scale is also used. The scale starts at the lowest temperature possible in the universe.

There is an absolute lowest temperature of -273ºC

This is where particles have no energy at all and, therefore, are not moving at all.

0 kelvin = -273ºC

higher temperatures means higher pressure.

pressure₁ / kelvin₁ = pressure₂ / kelvin₂

pressure₁  * volume₁ = pressure₂ * volume₂

Section 6 - Magnetism and Electromagnetism:

Magnetically hard material - retains its magnetism for a long time. It is also hard to demagnetize.

Magnetically soft material - loses its magnetism almost as soon as it leaves the magnetic field.

Magnetic field lines represent the direction (through the direction of the lines) and magnitude (through the density of lines) of a magnetic field on a single North Pole.  

The three pictures above show the magnetic field lines present in the presence of bar magnets.

The two pictures shown to the left show the magnetic field lines of a straight wire and a solenoid. The direction of the magnetic field lines can be shown by using the right-hand grip rule shown on the first picture to the left.

A coil of wire carrying current acts like a magnet and as such has filed lines as shown to the left. 

The way to test for the magnetic field lines and its direction is by using a compass. The compass will point always in the direction of the magnetic field line. You can then draw dots at the end points of the compass and connect the dots to show the magnetic field lines.

To increase the strength of the magnetism you can:

1. Increase current
2. Increase the number of coils in the wire
3. Adding a magnetic soft material in the solenoid

An electromagnet is created by wrapping a soft magnetic material with a current carrying wire. These are then used in relays and circuit breakers.

How do Electric Motors work:

1. A wire in a magnetic field feels a force and so turns.
2. This turns the split ring commutator.
3. The commutator reverses the current every half turn.
4. The wire continues to spin until the current is switched off.

How do Loud Speakers work:

1. A wire is pushed forwards and then moves back and forwards hundreds of times a second.
2. This pushes the cone / diaphragm.
3. Noise is created.

These both work because of the motor effect. When there is a magnetic field and current then a force will be created. Fleming’s left-hand rule is used to see which direction the force is in.

The picture below shows Fleming’s left-hand rule:

The motor effect can be increased by:

1. Increasing the amount of coils, the magnetic field strength or current strength.
2. Add a magnetically soft material in the centre.

Moving a wire back and forth across a field will induce a voltage.

Ways to increase the voltage are to increase the field strength, quicken the movement or increase the number of coils in the wire.

How do transformers work:

1. An AC current passes through a coil wrapped around a soft iron core (electro-magnet).
2. This induces a magnetic field.
3. The magnetic field makes a second wire move back and forth, creating voltage.

Step up transformers - this has fewer turns in the first wire compared to the second thereby creating a higher voltage and lower current as the output.

Step down transformers - this has more turns in the first wire compared to the second thereby creating a lower voltage and higher current as the output.

How is this used:

Transformers are used to change the voltage and current of electricity. Below shows one example of how transformers are used to deliver electricity to our homes safely:

power plant —> step up transformer (to avoid heat from high current) —> power lines —> step down transformer —> distribution lines —> homes

input (primary) voltage / output (secondary) voltage = primary turns / secondary turns

Vp * Ip = Vs * Is

primary voltage * primary current = secondary voltage * secondary current

The above only occurs, however, if the transformer is 100% efficient

Section 7 - Radioactivity and Particles:

Atomic number - the number of protons in the nucleus

Mass number - the number of protons and neutrons in the nucleus

Alpha, beta and gamma rays are all radiation that damages cells (ionises) and is emitted from unstable (full) nuclei.

Alpha - this type of radiation contains 2 neutrons and 2 protons which make it essentially the helium nucleus. This is the weakness type of radiation and cannot even penetrate paper.

Beta - this type of radiation contains only electrons created when a neutron turns into a proton and electron. This is stronger than the alpha radiation but cannot penetrate anything above aluminium.

Gamma - this type of radiation is part of the electromagnetic spectrum. It is very strong but cannot penetrate lead.

Alpha = -2 atomic number, -4 mass number

Beta = +1 atomic number, -1 neutron number, -0 mass number

Gamma = N/A

Uranium (Atomic number of 92, mass number of 235) —> Thorium (Atomic number of 90, mass number of 231) + alpha (atomic number of 2, mass number of 4)

Carbon (Atomic number of 6, mass number of 14) —> Nitrogen (atomic number of 7, mass number of 14) + beta (atomic number of 0, mass number of 0)

Radiation:

Ionising radiation imprints on camera film.

The Geiger-Muller detector beeps in the presence of radiation.

Background Radiation Examples:

• Radon gas in the ground.
• Cosmic rays
• Food and drink
• Buildings
• Boron in the soil
• Medical instruments.

The radiation from a radioactive source will decrease over time. The half-life is the time taken for the radiation to decrease by a half. It is different for different sources of radiation.

Uses of radiation:

1. Tracers - a radioactive source is put into a system such as a piping network. It will then build up at the blockage and can then be detected to tell people where the fault is.
2. Medical tracers - these are similar to the normal tracer except that these are put int a body. The radioactive source builds up, for example, at a blocked blood vessel and doctors will then know where to operate on.
3. Radiotherapy - radiation is used to target cancer cells.
4. Carbon dating - the amount of radiation is measured and carbon’s half-life is used to date the object.

Dangers of radiation:

Radiation can damage the structure of the cells DNA, when these damaged cells replicate, cancerous tissue may form. Therefore, some radiation is said to be carcinogenic. It damaged cells and tissues by changing their atomic structure, thereby causing them to stop functioning properly.

Radioactive waste can poison waters, destroy ecosystems and cause widespread harm to nature.

Experiment involving the alpha particles:

Rutherford designed an experiment which his two assistants Geiger and Marsden carried out.

Geiger and Marsden beamed alpha particles at a gold foil. They expected the particles to go straight through the gold foil. However, they found, rather surprisingly, that a few went through but emerged at a bent angle, some even got deflected. Using this surprising result, Rutherford formed out present day view of atoms. This new model explained why the positive alpha particles were sometimes repelled and why the faster they went the faster they were repelled.

Nuclear fission:

The nucleus of a uranium-235 atom can be split through fission whereby a neutron is fired at the uranium. This splits the uranium nuclei into 2, leaving 2 ‘daughter nuclei’ and some neutrons. These neutrons are then used to cause a chain reaction through hitting other uranium nuclei.

In nuclear fission, control rods are used to absorb neutrons to prevent there being too many of them. If there were too many neutrons then the reaction would get out of hand.

A moderator is also used. This is usually water and is used to slow the neutrons down enough to be able to hit the nuclei at the right speed.

So that's all there is to IGCSE Physics. Once again now all you have to do is learn these notes, memorise them and then you're done.



Good luck in your exams!

PS. I've attached a complete copy in case you're too lazy to read it from the blog (it has a mighty 32 pages).

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