P7 - Electromagnetism Flashcards
What is a magnet?
Material/object that produces a magnetic field
What 3 things do magnets have in common?
- Poles: north and south pole
- Surrounded by magnetic field
- Field lines go from north to south pole
If the field lines closer, what does this mean?
The magnetic field is stronger
What is magnetic material? Give examples.
- Any object that can be influenced by magnetic fields
- Has potential to become magnetic
- Nickel, cobalt, iron and steel
What are permanent magnets?
Produce their own magnetic field at all times
What are induced magnets?
- Only have their magnetic field temporarily
- Magnetic material comes into contact with field of permanent magnet causing it to gain it’s own field
What is electromagnetism?
- Electric currents produce own magnetic fields
- Only magnetic when current provided through the wire
Electromagnetism in wires:
- Current flow from bottom to top
- Magnetic field is all around wire (circles)
- Find out direction of magnetic field using right hand rule
Electromagnetism in a solenoid:
- Solenoid: wire coiled into spiral shape
- Magnetic field is strong and uniform
- Field lines point out at north pole and point in at south pole
How do you reverse the direction of the magnetic field in an electromagnet?
Reverse direction current flows
(poles also switch)
What are four ways to increase strength of an electromagnet?
- Increase current
- Increase number of turns
- Decrease length of coil
- Add iron core to inside of coil
What is the motor effect?
- A wire carrying current in the presence of a magnetic field
- produces a force
- Magnetic field of wire interacts with other magnetic field
- Force acts on wire, pushing it out of the field
- To feel full force, wire has to be 90 degrees to magnetic field
How do you find the direction of the force in the motor effect?
Use Flemming’s left hand rule
Split ring commutator:
-Swaps positive and negative connections every half turn
- Direction of current swaps every half turn
- Forces on coil always act in same direction
- Coil always rotates in same direction
How do you increase rotation speed in an electric motor?
- Increase current
- Add more turns to coil
- Increase magnetic flux density
Generator effect:
- coil between a magnetic field
- move coil
- induce potential difference field in wire
- generates current
What are three ways to increase the size of the induced potential difference?
- Change strength of magnetic field
- Move the wire/ magnet faster
- Shape wire into proper coil
What are the two different types of generators? What are the differences?
Alternators: slip rings and brushes –> alternating current
Dynamos: split ring commutator –> direct current
How do alternators work?
- The coil of wire rotates relative to the magnets, this induces a magnetic field in the coil, which then induces a voltage and current in the coil.
- The slip rings and brushes mean that contacts don’t swap every half turn
- This means that they produce an alternating potential difference and an alternating current
How do dynamos work?
- As the coil of wire spins relative to the magnet, a magnetic field, and hence a voltage and current, is induced in the coil.
- Split ring commutator means that the contacts swap every half turn.
- This means that they produce a direct potential difference and hence a direct current (d.c.)
How transformers work?
- Alternating pd at primary coil
-2. Cause current to flow - Forms magnetic field around coil
- Iron core is induced and gains magnetic field
- Iron core induces pd at secondary coil
- current flows
