Section 6 - Magnetism And Electomagnetism Flashcards
What do opposite magnets poles do?
Attract
Similar poles
Repel
Magnetic field definition
A magnetic field is a region where a magnetic pole experiences a force acting on it
Field line directions
North to south
How to draw magnetic fields
Two circles from north to south either side
3-4 lines leading in and out of poles
Lines shouldn’t cross
Add arrows to show direction
How do magnetic field diagrams show the strength of the field?
The spacing of field lines show it’s relative strength.
Magnetic field is stronger near the poles
Force of attraction
Two unlike poles - shown by connecting field lines between magnets
Force of repulsion
Between similar poles
Shown field line diverging away from each other
Magnetic materials
Magnetic materials experience a force in a magnetic field. The force between a magnet and a magnetic material is always attraction.
Examples of magnetic materials
Iron, steel, nickel, cobalt
How can Magnetic materials can become induced magnets? -
- Permanent magnets produce their own magnetic fields
- Magnetic materials in a magnetic field become induced magnets
- Induced magnets have their own poles
- Induced magnets only produce a magnetic field when in another magnetic field
What are temporary magnets?
These are magnets made of materials that can lose and gain magnetic charge quickly e.g. soft iron
Does an electric current have a magnetic field?
Yes, when it flows
How do you check the direction of a magnetic field in a wire?
right hand grip rule, thumb in the direction of the current.
What is a solenoid?
A solenoid is a current carrying wire into a coil.
What is the magnetic field direction in a solenoid?
Inside the solenoid it is straight. Outside the solenoid has a north and South Pole like a bar magnet.
How can you test and draw magnetic fields?
Use plotting compasses or iron fillings
What two things make an electromagnet?
A solenoid and a soft iron core
How does a electromagnet work?
The soft iron core becomes an induced magnet and adds to the overall magnetic charge
Three advantage of electromagnets
- turned on and off quickly
- made a lot stronger than permanent magnets
- you can vary their strength
What are relays?
Electric switched used in circuits. They are two or more electrically isolated circuits
Advantages of using a relay - 2
- a small current circuit can be used safely to turn on a large current circuit
- the low current circuit can use components that only work with small current
Passing a current through a wire produces a magnetic field. What happens when that wire is placed in another magnetic field?
The fields interact and a force is exerted on the wire which causes the wire to move.
What is the name of the effect when a wire is moved by a force exerted on it by a magnetic field?
The Motor effect
What is the motor effect?
The motor effect is when a current carrying wire interacts with another magnetic field at 90° to create motion
What happens when the wire and magnetic field run parallel in the motor effect
It won’t experience any force
How can you reverse the direction of force in the wire in motor effect?
Reverse the direction of current or Reverse the direction of the magnetic field.
How can you find the direction of motion, current or the magnetic field in the motor effect?
Using Flemings left hand rule. Thumb - Motion, First finger - field, second finger - current
How can the turning effect of a coil be increased? - 3 ways
- Increasing the current in the coil
- Increasing the number of turns on the coil
- Increasing the strength of the magnetic field
What happens when you twist a current carrying wire into a coil and put it into a magnetic field? What is the name of this process?
This created a turning effect, this makes a D.C motor
What is electromagnetic induction?
Electromagnetic induction is the creation of an emf ( and current in a full circuit) in a conductor which is experiencing a change in magnetic field or which is moving relative to a magnetic field
How can you induce an emf in a straight wire?
You can do this by placing it near a magnet and either moving the magnet or the wire
How can you induce an emf in a coil of wire?
Push a magnet through the coil of wire. If you connect a voltmeter you can see the magnitude and direction of the emf
What are the three ways you can increase the magnitude of induced emf?
- increasing speed of movement
-increasing strength of magnet
-increase number if turns on the coil
What happens when a change in magnetic field induced a current on a wire?
A magnetic field is created on the wire when a current flows, this magnetic field acts against the magnetic field that made it. It’s is trying to repel the magnet and return things to how they were. This is 5e generator effect
What is the name of the effect when a current is created due to inducing a magnetic field on a complete circuit?
The generator effect
What is the generator effect?
When a current is created because a magnetic field is induced on a complete circuit
What is an AC generator?
A generator is a coil in a magnetic field that produces a turning effect once a current is induced on it?
How does a AC generator work?
- An force is applied to the coil to rotate it causing an emf - and therefore a current - to be induced.
- Slip rings and brushes are used so that the contacts don’t swap every half turn like a motor.
- This means the current change direction - so it produces a.c
When is the voltage output greatest in an AC generator?
When the coil is parallel to the field lines because it is cutting through them at the fastest rate.
What is the transformer equation?
Input primary voltage / output secondary voltage = number of primary turns / number of secondary turns
Formula for power in electricity
P = I^2R or P = IV
If power before is power after in a transformer what is the equation
Ip x Vp = Is x Vs
What are the differences between a motor and generator?
Motors are DC generators are AC
Motors use a split ring commutator
Generators use slip rings and brushes
