Electromagnetism is caused by the magnetic fields around electric currents. The fields can cause forces with other nearby magnets and these forces can be used to make motors spin.
A wire carrying a current in a magnetic field feels a force. What is this effect called?
The motor effect
The generator effect
What is the angle between the force and the current flow that feels this force when it is in a magnetic field?
They are parallel
What is the unit for ‘magnetic field strength’?
Which of these will NOT increase the force on a current-carrying wire in a magnetic field?
Increasing the current
Reversing the magnetic field
Extending the length of wire in the field
What happens to the force if the current direction in a magnetic field is reversed?
The force disappears completely
The force decreases
The force direction reverses
When using Fleming's left-hand rule, what does the thumb represent?
0.4 A flows in 0.1 m of wire in a 0.7 T magnetic field. What force acts on the wire?
In a dc motor, what is the function of the split ring commutator?
It reverses the current direction every half turn, to keep the motor spinning in the same direction all the time
It shields the magnetic field from acting outside the motor case
It strengthens the magnetic field to make the motor spin fast on a lower current
Why do the opposite sides of the coil in a dc motor feel forces in opposite directions?
The current in each side is in opposite directions
The current in each side is in the same direction
The commutator switches the current direction every half turn
In a dc motor the commutator disconnects the current every half turn. Why doesn’t the motor stop?
The magnetic field goes off simultaneously
The coil’s momentum keeps it rotating
Gravity pulls one arm of the coil down