Magnet has two poles. North Pole and South Pole
| Permanent Magnets – | Temporary Magnets – |
| Do not loose their magnetism | Can be magnetised and demagnetised. |
| eg: Bar Magnet | eg Iron, Steel. |
It is the solenoid wound around an iron core. When the current is passed through a solenoid, the iron core becomes magnetised.
It is an electromagnet which magnetised with a large flow of current and attracts the switch towards itself turning off the current.
It has an electromagnet which is magnetised and then attracts the scap.
When a current carrying wire is placed in a magnetic field, it experiences a force.
Force can be increased by :
F – Force on the conductor
B – Magnetic Flux density
I – Current flowing through the conductor
L – Length of the conductor
First Finger:- Magnetic Field
Center Finger: Current
Thumb: Direction of Force
When a current passes through a coil placed in a magnetic field, the coil experiences a force and starts to rotate. The direction of force is given by left hand rule.
Current is switched on it generated a magnet field which interact with the permanent magnetic field and produces force. When the current reverses the direction of force reverses generating sound waves.
It is the device which is used to increase (step up) or decrease the voltage (step down) or the potential difference.
Input Voltage
Output Voltage
= VP/VS=NP/NS
Vp = Voltage across primary coil
Vs = Voltage across secondary coil
Np = Number of turns in primary
Ns = Number of turns in secondary
If the number of turn in primary is 20 and input voltage is 230 V, What are the number of turns in secondary if the voltage generated in secondary is 460 V?
Vp = 230V Np = 60
Vs = 460V Ns = ?
=
Ns = Np x Vs/ Vp
= 20 x 460/ 230
= 40 turns
A transformer input voltage is 230 V and the current is 20 A. What is the output voltage if the output current is 10A.
Vp = 230V Vs = ?
Ip = 20A Is = 10A
Vp x Ip = Vs x Is
230 x 20 = Vs x 10
230 x 20/10 = 460V
Increasing voltage for transmission increases the voltage and decreases the current High current causes heating and results in loss of energy. By increasing the voltage, current is lowered and energy loss is prevented so transmission is efficient.
H x I2
| STEP UP TRANSFORMER | STEP DOWN TRANSFORMER |
| Increase the voltage | Decrease the voltage |
| It has more turns in secondary than in primary. | It has more turns in primary than in secondary |
| Voltage in secondary is greater = Is x Ns ↑ | Voltage in secondary is lower = Is x Ns ↓ |
| Connected next to the power station to transmit high voltage to reduce the heating effects of current during transmission. | Connected to the power supply before it reaches homes to reduce the voltage to 230 V. |
Magnet – A magnet is a material or an object that produces a magnetic field. Magnet has two poles – North Pole and South Pole
Magnetic Field Lines – The magnetic field lines are a visual tool used to represent magnetic fields. Field lines are from north pole to south pole.
Induce Magnetism – When a piece of non-magnetized magnetic material touches or approaches the pole of a permanent magnet, it becomes a magnet in itself.
North Pole – One end of the compass needle points in the North direction and is called the North Pole of the magnet
South Pole – One end of the compass needle points in the South direction and is called the South Pole of the magnet.
Solenoid – Solenoid is a coil of wire.
Electromagnets – It is the solenoid wound around an iron core.
Relay – A relay is an electric or electromechanical switch consisting of an electromagnet, an ammateur, a spring and a set of electrical contacts.
Circuit Breaker – It is an electromagnet which magnetised with a large flow of current and attracts the switch towards itself turning off the current.
Motor Effect – Motion as a result of current in a magnetic field is called the motor effect.
Flemming Left Hand Rule – When a current passes through a coil placed in a magnetic field, the coil experiences a force and starts to rotate. The direction of force is given by left hand rule.
Magnetic Flux density – Magnetic flux density (B) is defined as the force acting per unit of current per unit of length in a cable placed at right angles to the magnetic field.
Split Ring Commutator – These are rings that allow the direct current to move in the opposite direction to maintain full rotation.
Electromagnetic Induction – It is the production of voltage or electromotive force due to a change in the magnetic field.
Generator Effect – Current is produced because of the motion of a conductor in the magnetic field. Mechanical energy is transformed to electrical energy.
Transformer – It is the device which is used to increase (step up) or decrease the voltage (step down) or the potential difference.
Step Up Transformer – It is the device which is used to increase (step up) or the potential difference.
Step Down Transformer – It is the device which is used to decrease the voltage (step down) or the potential difference.
Transformer Efficiency – Efficiency of a transformer can be defined as the output power divided by the input power.
National Grid – Electricity is transferred from the power plant to consumers via the National Grid
Disclaimer: I have tried by level best to provide the answers and video explanations to the best of my knowledge. All the answers and notes are written by me and if there is any similarity in the content then it is purely coincidental. But this is not an alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it.
References:
BBC Bitesize
Make sure you have watched the above videos and are familiar with the key definations before trying these questions. It is also good to time yourself while doing these questions so that you can work on the speed as well.