P4 Flashcards
What are the two poles of a magnet?
North and South.
What happens between like poles?
They repel.
What happens between opposite poles?
They attract.
What is a permanent magnet?
A magnet that is always magnetic and always has poles.
What is an induced magnet?
A material that becomes magnetic when near or stroked by a permanent magnet. - temporary
Which materials are commonly used as induced magnets?
Iron, Nickel, and Cobalt.
What causes a material to become magnetised?
The alignment of domains within the material in the same direction.
What do magnetic field lines show?
The direction and strength of a magnetic field — from north to south.
What does a greater concentration of field lines indicate?
stronger magnetic field.
What tool is used to map a magnetic field?
A plotting compass.
What produces Earth’s magnetic field?
Currents in the Earth’s magnetic core.
Why does a compass point North?
It aligns with Earth’s magnetic field lines.
What is unusual about Earth’s magnetic poles?
The magnetic south pole is near the geographic North Pole (in Canada).
What happens when current flows through a wire?
It produces a circular magnetic field around the wire.
How is the direction of an electromagnetic field determined?
Using the right-hand grip rule.
What increases the strength of this magnetic field?
Greater current and being closer to the wire.
What is a solenoid?
A coil of wire with current flowing through it, producing a magnetic field like a bar magnet.
What strengthens a solenoid’s magnetic field?
Inserting an iron core.
What factors affect a solenoid’s magnetic field strength?
• Size of current
• Length of coil
• Cross-sectional area
• Number of turns
• Type of core
What happens when two magnets interact?
They exert a magnetic force — attraction or repulsion.
Why does a wire experience force near a magnet?
Because the magnetic field from the magnet and the field around the wire interact.
What direction is the wire pushed?
At right angles to both the wire and the magnetic field.
What does Fleming’s Left-Hand Rule show?
The directions of Force, Magnetic Field, and Current — all at 90° to each other.
What does each finger represent for the Flemings left hand rule show?
Thumb - force direction
Pointer finger - field direction
Middle finger - current
What type of current does the Fleming left hand rule use?
Conventional current — from positive to negative (opposite to electron flow).
What is the formula for magnetic force?
F = B x I x L
(Force = magnetic flux density × current × length)
What is the unit of magnetic flux density?
Tesla (T) — number of flux lines per square metre.
What do electric motors use?
A coil of wire between fixed permanent magnets.
What happens to the coil in electric motors?
It rotates due to opposing magnetic forces on each side.
Why does the coil rotate in an electric motor?
One side moves up, the other down due to induced magnetic forces.
What causes a potential difference in a conductor?
A changing magnetic field causes electrons to move, building up charge.
What happens if the conductor is part of a complete circuit?
A current flows.
What direction is the induced magnetic field from the current?
In the opposite direction to the original field.
What do electric generators use?
A rotating coil between two permanent magnets.
What causes the coil to rotate in generators?
A turbine spinning the coil.
What happens as the coil spins in a generator?
It cuts through the magnetic field, inducing a potential difference.
What happens if the coil is in a complete circuit (generators)?
An alternating current (AC) flows.
What is alternating current?
Current that constantly changes direction.
What does changing direction of current also change?
The direction of the magnetic field produced.
What type of current do transformers need?
Alternating current (AC).
How does a transformer induce voltage?
The changing magnetic field from the primary coil cuts through the secondary coil.
What happens in the secondary coil?
An alternating current is induced.
What if the primary coil used direct current (DC)?
No voltage would be induced — no change in magnetic field.
What happens in a step-up transformer?
The secondary coil has more turns, increasing the voltage.
What happens in a step-down transformer?
The secondary coil has fewer turns, so voltage decreases.
What is the transformer equation?
number of coils on primary/number of coils on secondary = p.d of primary/p.d of secondary
When does the transformer equation apply to current?
Only if the transformer is 100% efficient.
What do microphones produce?
A current proportional to the sound signal.
What is inside a dynamic microphone?
A fixed magnet and a coil of wire that is free to move.
How is current induced in a microphone?
Sound wave pressure variations move the coil, which cuts the magnetic field.
What happens in a loudspeaker?
Current enters the coil → interacts with magnetic field → moves the coil and cone → produces sound waves.
