Electromagnetism Flashcards
Describe the shape of the magnetic field around a straight wire
A series of concentric circles
What does each finger represent in Fleming’s left and right hand rule?
Index: Field
Middle: Current
Thumb: Force/motion
How can you increase the field strength of a solenoid?
Increase the number of turns
Increase the current
What would happen if the current reversed direction through a solenoid?
The North and South poles would change positions
When do you use Fleming’s left hand rule?
If there is already a current flowing through a conductor and it has been placed in a magnetic field
When do you use Fleming’s right hand rule?
If a conductor is placed in a magnetic field and is moved to generate a current
How does an electric motor work?
A current flows through the coil and it is placed in a magnetic field. It therefore will experience a force acting on it. A force acts upwards on one side of the coil and downwards on the opposite side. The coil spins on its axis in a clockwise direction
What is the difference between a simple D.C motor and a simple A.C generator?
A D.C motor: Already has a current flowing through it and when placed in a magnetic field will experience a force that makes the coil spin
An A.C generator: There is no current flowing through it already. The coil is made to spin, by a turbine, in a magnetic field. It induces a voltage and therefore a current
What 4 factors affect the output voltage of a simple A.C generator?
Strength of the magnetic field
Speed that the coil spins
Surface area of the coil
Number of turns of the coil
How is an A.C induced in the secondary coil of a transformer?
An alternating current is used in the primary coil, thus creating an alternating magnetic field in the primary. It is directed into the secondary coil by the iron core. The changing magnetic field in the secondary coil induces a voltage and drives a current through the secondary
What is an alternating current?
A current that reverses its direction
What does A.C stand for?
Alternating current
If a transformer has less secondary coils than primary coils what type of transformer is it?
Step down
If a transformer has more secondary coils than primary coils what type of transformer is it?
Step up
How is energy loss kept to a minimum in transformers?
The iron core is made of thin sheets of iron to reduce induced current- minimise heat loss
Copper coils are thick so that resistance is low, reducing heat loss
