P4 Flashcards
What is strength flux density measured in?
Teslas (T)
What methods can you adapt to see magnetic field patterns?
- Iron fillings
2. Compass
Describe how to plot the magnetic field lines of a bar magnet with a compass.
- Put the magnet on a piece of paper and put a compass next to it, marking on the piece of paper the point which the compass needle points to.
- Then move the compass so that the tail of the compass needle is where the tip was previously
- Repeat and join markings for a complete sketch around the magnet
- Do this several times for different points around the magnet to get several field lines
Explain why a piece of copper is not attracted to or repelled by a magnet.
Copper is not magnetic material.
What is a magnetic field around a straight, current-carrying wire made up of?
How can find the direction of the field?
Concentric circles. Right hand rule.
In what way will the magnetic effect at the ends of the solenoid increase?
- current in wire
- number of turns
- cross sectional area of solenoid decreased
- length decreased
- iron core added
State what the thumb, first finger and second finger each represent in Fleming’s left- hand rule
Thumb: motion
First finger: field
Second finger: current
Describe the formula you could use to calculate the force acting on a current- carrying conductor.
F = BiL
Force on a conductor carrying a current (N) = magnetic flux density (T) x current (A) x length (m)
Under what circumstance will the wire not experience any force at all?
If the wire runs along the magnetic field.
State two properties that could be changed to decrease the speed of an electric motor.
Decrease current/ number of turns on coil/ magnetic flux density
When does electromagnetic induction happen?
When a potential difference is induced across a conductor which is experiencing a change it it’s external magnetic field.
State the difference about the current produced by alternators and dynamos.
Alternator produces a.c and dynamos produce d.c
How is a split ring commutator used in dynamos?
They swap the connection every half turn to keep the current flowing in the same direction, so it changes from a.c to d.c
What do transformers do?
They change the potential difference on an alternating current.
What are step down transformers?
They step the voltage down. They have more turns on the primary coil than the secondary coil.
