Motors And Solenoids

Question 1

what does a basic d.c motor look like

Answer 1

forces acting on the two side arms of the wire that are carrying the current

Question 2

what are the forces acting on the two side arms in a d.c motor

Answer 2

the usual forces which act on any current in a magnetic field

Question 3

why does the coil rotate in a d.c. motor

Answer 3

• because the forces acting on one side of the arm each are acting in opposite directions
• so they cause the arms to rotate

Question 4

what does the split ring communator do

Answer 4

• it swaps the contacts every half turn

- to keep the motor rotating in the same direction

Question 5

what are the two ways in which the direction of the motor can be changed

Answer 5

• by swapping the polarity of the d.c supply (reversing the current)
• or by swapping the magnetic poles over (reversing the field)

Question 6

what do you use to work out which way the coil will turn

Answer 6

Flemming’s left hand rule

Question 7

in a d.c. motor setup with a coil of wire being in between a south pole on the left and a north pole on the right, what is the direction of the flowing current and the motion of the coil of wire

Answer 7

• you would use flemming’s left hand rule
• you know the first finger field is pointing from north to south, so your first finger points to the left
• this means your second finger current is pointing away from you, showing the flow of current
• this makes your thumb point upwards, indicating the motion
• your thumb coils down ANTICLOCKWISE, so that is the movement of the coil of wire

Question 8

how can you increase the strength of a magnetic field created by a length of wire

Answer 8

• by wrapping it into a long coil with lots of loops

- creating a solenoid

Question 9

what are the field lines like inside a solenoid and what does it cause

Answer 9

• you get lots of field lines pointing in the same direction

- causes the magnetic field is strong and almost uniform

Question 10

what are the field lines like outside a solenoid and what does it cause

Answer 10

• overlapping field lines cancel each other out

- so the field is weak, apart from the ends of the solenoid

Question 11

what do the field lines of a solenoid look like in comparison to something else

Answer 11

• the field lines of a bar magnet

- with the magnetic field ‘flowing’ through and around to the other side

Question 12

what do the direction of the field lines depend on

Answer 12

the flow and direction of the current

Question 13

what is a solenoid and example of

Answer 13

an electromagnet

Question 14

what is an electromagnet

Answer 14

a magnet that can have its magnetic field turned on and off using an electric current

Question 15

what can you add to increase the magnetic field strength even more

Answer 15

• putting a block of iron at the center of the coil

- this iron becomes an induced magnet whenever a current is flowing