13) Electromagnetic Induction Flashcards
What is a current?
A flow of charge
What two ways can induce a potential difference?
Electrical conductor moving in a magnetic field
Changing magnetic field through electrical conductor
How does a changing magnetic field through an electrical conductor induce a p.d?
A changing magnetic field is a magnetic field with changing strength
If there is a magentic field through the middle of a coil of wire, it is ‘linked’ with the coil
A chaging magnetic field that is linked with a coil of wire induces a p.d. in that wire
What happens when a wire moves near a magnet?
A p.d is induced in the conductor
How can induced potential difference be increased? (2)
More coils Faster movment (magnetic field change)
What happens when a wire moves downwards in a horse show magnet?
A p.d is induced in the wire and an electric current flows through the wire
A force acts in the opposite direction to the action inducing the p.d
In which direction does a force induced by the motor effect run?
In an opposite direction to the inductive force
What is an AC generated by?
A rotating-coil generator
How does a rotating-coil generator work?
A coil of wire is rotated inside a fixed magnetic field
When the coil rotates it cuts across the magnetic field lines and a p.d is induced
The induced p.d causes a current to flow in the coil of wire
The faster the coils cuts across lines, the greater the magnitude of the induced p.d
What is a DC generated by?
A dynamo
How does a dynamo produce a DC?
A coil of wire rotates and the magnet is fixed
The coil rotates, this generates a p.d in one direction
The split-ring commutator reverses the direction of the current every half-turn of the coil. This makes sure that the current is always moving in the same direction to keep the coil rotating
When is the potential difference highest in dynamos?
WHen the coil and magnetic field are parallel
When is the potential difference 0 in a dynamo?
When the coil is perpendicular to the magnetic field
How do microphones work?
The sound waves that hit the microphone make a coil inside a magnet vibrate
The coil vibrates at the same frequency as the sound wave coming in
This induces a p.d and current in the coil
What can transformers do?
Change the voltage in wires carrying an AC
What are the 3 main parts of a transformer?
Primary coil
Secondary coil
Iron core
What is the transformer equation?
voltage across primary coil / voltage across secondary coil = primary coil turns / secondary coil turns
What are the 2 types of transformer?
Step up
Step down
What are features of a step-down transformer?
Ns < Np
Secondary coil has fewer turns than primary coil
Voltage across secondary coil is less than voltage across primary coil
What are features of a step-up transformer?
Ns > Np
Secondary coil has more turns than primary coil
Voltage across secondary coil is greater than the oltage across the primary coil
How do transformers work?
An AC p.d is applied to the primary coil
This causes an AC current to flow through the primary coil
The AC current creates a continously changing magnetic field in the iron core of the transformer
The changing magnetic field in the iron core also passes through the secondary coil
The changing magnetic field passing through the secondary coil induces an alternating p.d in the secondary coil
What voltage is electricity generated at?
15,000V
What voltage is electricity transmitted at?
400,000V
What does transmitting energy at higher voltages do?
Reduce energy lost as heat due to resistance in cables
What is the equation for power?
power = current x voltage
What would a 100% efficient transformer mean?
Power in primary coil = power is secondary coil
How do step-up transformers reduce energy loss?
Reduced current in secondary coil reduces energy lost as heat
What does a higher current mean for energy loss?
More energy loss
