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What is a permanent magnet? Name an example.
A type of magnet that will not lose its magnetism after the magnetic influence is removed. E.g. Steel.
What is a temporary magnet?
Type of magnet produced under a the influence of a current or another magnet.
What is an electromagnet?
An electromagnet is a magnet produced by an electric current using a solenoid.
How does the domain theory explain magnetism?
According to the theory, one of the quatum numbers is electrospin. The spin can be clock or anti-clock with iron, cobalt, or nickel. The electronic structure forms dipoles with the electrons forming a cluster with +ve and -ve at each end.
What is the domain theory?
It is the atomic theory as applied to magnetism. It explains magnetism using quantum mechanics.
What is quantum mechanics?
It is the more advanced form of atomic physics which contains special theories in the form of quantum numbers.
Describe an electric bell.
Switch on, current flows from cell to switch to EM to metal strip via contact screw to cell. Circuit complete.
Em magnetizes, attracts metal strip forward and strikes gong.
Contact screw broken, circuit broken, EM demagnetizes, metal strip released.
How does a motor work?
AB is pushed up, CD is pushed down.
Coil rotates by 2 equal and opposite forces, pushing it in a vertical position.
Momentum causes it to turn 180. On left, coil is given upwards push, right down. Coil rotates but not smoothly.
Describe a motor.
Converts electrical energy into mechanical energy.
Works on LHMR.
- 2 main parts:
- field magnets
Describe Lenz's Law.
States that the induced current is always such that it opposes the motion producing it.
Predicts completely the direction of the current and the magnetic field.
Describe the motor rule.
An electrical device capable of producing mechanical energy in rotery motion to drive certain appliacnes.
- 3 forces are at right angles to each other
- Motion - rotation - work
Describe a galvanometer.
- Works on the principle of EC motor (LHMR).
- Started revolution of instruments and signs of instrumentation.
- most gauges work on principle of gal.
- Measuring device for mA and um.
- Consists of rectangular coil. Current enters coil via spring and leaves through other.
- If current on ab is up, cd is down. Ab vorce is out, cd force is in. Equal and opposite forces. Deflection is proportional to current.
Describe a relay.
Switch that turns current on or off, operated magnetically by a current flowing in a seperate directiom.
Important device, every device probably has one.
- Pri and sec circuits. Pri activates sec electronically.
- Pri switch off = circuit complete
- Pri switch on, complete circuit, EM magnetizes, metal strip - secondary, circuit cut off, switch off
Describe the LHSR.
Solenoid = cylindrical coil
Cylinder is soft iron w/ coil wrapped around it
LHSR links current with MF
Solenoid behaves like bar magnet with S and N at each end.
- Thumb = N
- Curled fingers = direction of current
Describe the LHTR.
EC always has an associated magnetic field (EC current always has a magnetic field).
Shape of magnetic field depends on the shape of the conductor.
LHTR links current flowing in a straight conductor to its magnetic field.
- Thumb = direction of current.
- Curled fingers = direction of magnetic force.
What is a generator?
A generator produces an electrical current.
- Magnetic field
- Electric current
Describe an A.C. generator.
- 1. In the vertical position, there is no current (No motion possible).
- 2. Coil is rotated clockwise - rotated from 0 to 90. Current increases from 0 to max. Current is out (+ve).
- 3. Coil rotates from 90 to 180. Current decreases from max to 0. (ZY is always connected to x, which is connected to A.
Describe a DC generator.
- 1. In the vertical position, there is no current.
- 2. From 0 - 90, current is out. Current increases from 0 to max.
- 3. Current decreases from max to 0. From 1 - 180, brush A is connected to Y, current is out.
- 4. From 180 - 360, brush A is connected to X, therefore current is out.
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