P7: Electromagnetism Flashcards
1
Q
How can you increase the strength of a magnetic field?
A
- Increase current
- Increase number of coils on a wire
- Inserting iron bar in centre
2
Q
How can you reverse the direction of a magnetic field?
A
- Reverse the direction of the current
- Wind coils in the opposite direction
- Reverse the direction of the magnet
3
Q
How do you know which pole is which?
A
Look at the end of the coil:
- If current is flowing clockwise, that end is south
- If current is flowing anticlockwise, that end is north
4
Q
What direction do field lines go?
A
From north to south.
5
Q
What is a solenoid?
A
A spiral of insulated, conducting wire wound around a cylinder.
6
Q
How does a scrapyard crane work?
A
- Scrap vehicles lifted by powerful electromagnets attached to cranes
- Steel frame sticks to it when current passes through coil of electromagnet
- When switched off, vehicle falls
7
Q
How does a circuit breaker work?
A
- Switch is held closed by a spring
- When current is too large, switch is pulled open by electromagnet
- It stays open until closed manually
8
Q
How does an electric bell work?
A
- When connected to battery, iron armature is pulled to electromagnet
- This opens make-or-break switch & electromagnet is switched off
- This makes iron armature spring back and the make-or-break switch closes again, causing cycle to repeat
