1. Physics IGCSE Revision
(Part 3)
By: Momina

2. Brief Intro on Magnets
Magnetic material- is a type of material that
can be magnetized and is attracted to other
magnets.
Strong metals contain
1- iron
They are called
2- nickel “Ferromagnetics”
3- cobalt Iron and alloys of iron are
called ferrous. (Ferrous in
Latin means iron)
Aluminium, copper, and other
non-magnets are called non-
ferrous.

3. 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.

4. 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)

5. 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.

6. Right-hand grip rule

7. Electromagnets
• These are types of magnets that can be
switched on and off.
Coils
Iron core
The strength of the magnetic field can be increased by:
- Increasing the current.
- Increasing the number of turns in the coil

8. Magnetic Relay
Metal
contacts.
• 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.

9. Circuit Breaker
Circuit 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.

10. 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
Force is increased if:
the field. It is not -Current is increased
attracted to it. -Stronger magnet is used
-Length of wire in field is
increased.

11. Flemings Left Hand Rule

12. Electric motors
An electric motor transfers electrical energy to
kinetic energy.
• 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. Improve turning effect

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

14. 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.

15. Induced Currents
Fleming’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

16. Generators
• The coil rotates
• Magnetic fields are cut
• EMF is generated
• Causes current to flow
• Coil rotates– upwards,
Increasing EMF:
downwards, upwards - Increasing the number of
causing the current to turns on coil
flow backwards, - Increasing area of coil
forwards, backwards. - Use stronger magnet
- Rotate coil faster

17. 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.

18. 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
output voltage Turns in output coil inducing an alternating
= voltage in the output coil.
Input voltage Turns on input coil

19. Step-up and Step-down transformers
Step-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.

20. Power Through a Transformer
Input x Input = Output x Output
voltage current voltage current

21. Summary
Transformers:
Current + Motion=Magnetic Field
Electromagnetic Induction:
Magnetic Field + Motion = Current
Generator (Electric Motor):
Current + Magnetic Field = Motion

22. Important electronic components
1. Resistors – keep currents + voltages at levels
desired by the electronic component
2. Capacitor – store small amounts of electric
charge
3. Diodes – allow the current to flow in only one
direction
4. Light-emittingg diodes (LED) – glow when a
small current is passed through them.

23. Continued…
5. Transistors – used to amplify signals
6. Integrated circuits(micro-chips)– contain complete circuits with :
a) Resistors
b) Transistors
c) Other components
7. Relays– electromagnetic switches.

24. 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 1 Output
resister

25. Potential Divider
• A potential divider only delivers a portion of
the voltage.

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

27. Transistors as switches
• It is a Collector
semiconductor
device made of
silicon.
Base
Emitter

28. The NPN resistor
1000 ohms c 6V
b
e
• 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 flow
2. Input the base greater than 0.6Vlamp switches on
3. 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.

29. Logic Gates

30. 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.

31. 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)

32. • 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

33. Atoms

34. Nuclear Radiation

35. 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

36. 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.

37. 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.

38. In a Magnetic Field

39. 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

40. Radioactive decay- Alpha Decay

41. Radioactive decay- Beta Decay

42. Half-Life
• This is the amount of time taken for the nuclei
of a radioactive substance to decay.

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

44. Nuclear Fission

45. What can Radioactivity be used for?
1. Tracers
2. Radiotherapy
3. Testing for cracks
4. Thickness monitoring
5. 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

46. This is the physics syllabus Complete
Best of luck for
your IGCSE exams
Especially my fellow candidates of May/June 2011!!!