Magnetic Fields in Wires & Solenoids Flashcards
All 6 cards in this deck
What is the magnetic field pattern around a straight wire carrying a current?
Concentric circles centred on the wire, at right angles to it. The circles are closer together (field is stronger) nearer the wire.
Which rule gives the direction of the magnetic field around a straight current-carrying wire, and how is it used?
The right-hand grip rule: point the right thumb along the (conventional) current, and the curled fingers show the direction of the field.
What are the steps to demonstrate the magnetic effect of a current?
e.g. a straight wire passed vertically through a card
- Place a plotting compass next to the wire with no current — it points north.
- Switch the current on — the compass needle deflects, showing a magnetic field is produced.
- Increase the current, or move the compass closer to the wire — the deflection increases, showing the field is stronger.
Describe the magnetic field of a solenoid carrying a current.
Inside: strong and uniform (evenly spaced parallel field lines). Outside: the same shape as the field of a bar magnet.
What is an electromagnet?
A solenoid with an iron core. The turns of the coil add their fields together and the iron core makes the field much stronger.
In a relay, what happens when a current flows in the input circuit?
The electromagnet is switched on and attracts an iron armature, which closes the contacts (switch) in the second circuit.