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UPPCS Physics Gap Sheet: Magnetism and Electromagnetic Induction.
UPPCS has asked 13 of these. 18 have not been asked yet. Lock the first list, then read the second: it holds what UPPCS has not used yet.
First, the concept
Magnets have north and south poles together. Electric current also creates a magnetic field, and that field can exert a force on another current. These links explain electromagnets and electric motors.
A changing magnetic flux induces an electromotive force. Lenz law gives its opposing direction; energy conservation explains that opposition. Generators and transformers use induction, while motors use magnetic force on current.
✅ Already asked (13)
Magnets and materials
- Like and unlike poles · Like poles repel; unlike poles attract.
- Cutting a bar magnet · Each piece becomes a complete magnet with both poles.
- Ferromagnetic metals · Iron, cobalt and nickel are strongly attracted by magnets.
- Diamagnetism · Bismuth and copper are weakly repelled by a magnetic field.
- Paramagnetism · Aluminium and oxygen are weakly attracted in a magnetic field.
Current and magnetic force
- Solenoid · A current-carrying coil behaves like a bar magnet; reversing current reverses its poles.
- More coil turns · With the same length and current, more turns make a solenoid's field stronger.
- Electromagnet strength · Higher current and a suitable iron core increase field strength.
- Fleming left-hand rule · Gives the force direction on a current-carrying conductor in a magnetic field.
Induction and Earth
- Faraday induction · Changing magnetic flux through a circuit induces an electromotive force.
- Laminated transformer core · Insulated thin layers reduce eddy-current losses.
- Mutual induction · Changing current in one coil can induce voltage in a nearby coil.
Further magnetic applications
- Magnetic levitation · Magnetic forces can support a body without mechanical contact.
❌ Not asked yet (18)
Magnets and materials
- Field lines · Outside a magnet they run from north to south; inside they return from south to north.
- Magnetic-field strength · Closer field lines indicate a stronger field; lines never intersect.
- Soft iron core · Easy magnetisation and demagnetisation make it useful for electromagnets.
- Steel permanent magnet · Steel retains magnetisation better than soft iron.
- Heating a magnet · Heating above the Curie temperature destroys ferromagnetic order.
Current and magnetic force
- Oersted observation · A current-carrying wire deflects a nearby magnetic compass.
- Right-hand thumb rule · Thumb gives current direction; curled fingers give the surrounding field direction.
- Electric bell · An electromagnet repeatedly attracts an armature as a contact opens and closes.
Induction and Earth
- Lenz law · The induced current opposes the change causing it, consistent with energy conservation.
- Fleming right-hand rule · Gives induced-current direction for a conductor moving through a magnetic field.
- Eddy currents · Circulating induced currents arise in bulk conductors and can cause heating or magnetic braking.
- Magnetic dip · The dip angle is zero at the magnetic equator and about 90° at magnetic poles.
- Magnetic declination · The angle between magnetic north and geographic north varies with place and time.
Further magnetic applications
- Induction cooker · A changing magnetic field heats suitable cookware through induced currents and other magnetic losses.
- Magnetic shielding · High-permeability material can redirect magnetic flux away from a protected region.
- Magnetic domains · Alignment of many domains produces strong magnetisation in a ferromagnet.
- Magnetic compass near a wire · Reversing current reverses the compass deflection caused by the wire.
- Transformer frequency · An ordinary transformer changes voltage but keeps the supply frequency unchanged.
⚠️ A stationary magnet beside a stationary coil does not continuously induce current. Aluminium is weakly paramagnetic, though an ordinary magnet does not noticeably attract it.
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