magnestism, motor effect and electromagnetic induction

physics edexcel

how do you ncrease the strength of an electromagnet

1. increase the current in the wire

2. increase the turns of the wire

3. add an iron core

what happens when a current carrying wire is put in a magnetic field

the carrying conductor experiences a force from the permanent magnets

why is the force in a dc motor equal and opposite on both sides

because the current on each side of the coil is flowing in opposite directions

what happens when the coil in a dc motor reaches 180 degrees

the current must be reversed

what happens in a dc motor to prevent the coil from coming to a stop.

the split ring commutator swaps the positive and negative connections every half turn. This means the direction of the current swaps every half turn. This means the force acting on the wire will always be in the same direction.

what can we do to a dc motor to get it to spin in the opposite direction

1. reverse the direction of the current

2. reverse the direction of the magnetic field lines

what can we do to make the motor spin faster

1. increase the current

2. increase the magnetic flux density (field lines)

3. increase the number of turns in the coil

how can you induce potential difference

1. move a coil of wire in a magnetic field

2. move a magnet into a coil of wire

-for this to work something needs to be moving

explain induced current

1. a magnet has a magnetic field around it

2. a wire is moved into the mag field or a magnet is moved into coil of wire

3. the magnetic field lines are cut by the wire

4. this induces a potential difference

5. if the wire is part of a completed circuit the induced potential difference induces a current

how to increase the induced potential difference

1. faster movement of moving coil or magnet

2. stronger magnetic field

3. more turns on the coil

4. larger area of coils

what is lenz’s law

the induced voltage produces an induced current if the conductor is connected in a complete circuit. the induced current creates a magnetic field around itself. This induced magnetic field opposes the movement inducing the current.

what is a dynamo

a DC motor in reverse

how is pd induced in a dynamo

the spinning coil experiences a changing magnetic field so pd is induced.

when is the highest pd in a DC motor

when the coil is at 90 degreed to the mag field

what happens when the coil is at 90 degrees to the direction of mag field in a Dc motor

no potential difference is induced

what is an alternator

an AC generator

what does an alternator have in it

it has commutator rings and brushes. due to no split ring commutator, the current reverses every half turn

explain how a dynamo works

1. a coil of wire rotates in a magnetic field

2. the coil of wire experiences a changing magnetic field

3. as one side of the wire moves up through the magnetic field, the magnetic field lines are cut by the wire

4. this induces a potential difference

5. because the wire is part of a complete circuit, the induced pd induces a current.

6. the split ring commutator ensures the induced current always flows in the same direction

explain how an alternator works

1. a coil of wire rotates in a magnetic field

2. the coil of wire experiences a changing magnetic field

3. as one side of the wire moves up through the magnetic field, the magnetic field lines are cut by the wire

4. as this side of the wire moves down through the magnetic field, the magnetic field lines are cut in the opposite direction by the wire.

5. this induces an alternating potential difference.

6. because the wire is part of a complete circuit the induced potential difference induces a current which is an alternating current

what does a loudspeaker contain

a coil that vibrates a speaker cone when AC flows through it

what effect does the loud speaker use

the motor effect

how does a loudpseaker work

1. a cone wrapped in a wire is connected to an ac power supply and is placed in a permanent magnetic field

2. when current flows through the wire it creates a magnetic field which interacts with the permanent magnetic field

3. this produces a force which causes the cone to vibrate, producing sound

how does a microphone work

1. the microphone converts sound waves into electrical signals

2. sound waves cause a flexible diaphragm to vibrate

3. the vibration then causes a coil to move backwards an forwards around a permanent magnet

4. because the coils cutting across the magnetic field lines, the coil experiences a changing magnetic field

5. this then induces a potential difference

6. this is an alternating potential difference due to the continual change of direction of the coil

7. because the coil is in a complete circuit, this induced pd then induces a current

8. this current is an ac current and is the electrical output from the microphone

what effect does the microphone use

the generator effect

what does a step up transfromer do and why

increases the alternating voltage so less energy is lost when sending it across the country

what is a step down transformer do and why

reduces the alternating voltage so it will work in people houses without being dangerous

what does a transformer consists of

a primary coil, a secondary coil and an iron core

why is iron used

as it is easily magnestised

how does the transformer work

1. a primary voltage drives an alternating current through the primary coil.

2. the current through the primary coil produces a magnetic field which changes as the current changes direction

3. the iron core increases the strength of the magnetic field

4. the magnetic field passes through the secondary coil

5. the changing magnetic field induces a changing potential difference in the secondary coil

6. the induced potential difference produces an alternating current in the external circuit

what can transformers only work with

an alternating current

how has the national grid ensured the minimum amount of energy is lost

1. the cables are thick and their resistance is low

2. supplies are stepped up to give high voltages in the wires to reduce the current through transmission wires

how do microphones work in simple terms

it converts pressure variations in sound waves into an alternating current

how do loudspeakers work in simple terms

convert variations in the current of an electrical circuit into the pressure variations which produce audible sound