Physics - EDEXCEL IGCSE - Finished

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).

Click Here

Physics - EDEXCEL IGCSE - Radioactivity and Particles

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.

Physics - EDEXCEL IGCSE - Magnetism and Electromagnetism

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