electric motors

Question 1

what is the basis of an electric motor?

Answer 1

a coil of wire carrying a current in a magnetic field tends to rotate

Question 2

why does it rotate?

Answer 2

because the coil is on an axle and the forces act one up and one down

Question 3

what happens when a loop of wire is placed in a magnetic field and what does it mean?

Answer 3

there is a moment on both sides, meaning loop will rotate in clockwise direction

Question 4

why does the coil start to spin clockwise?

Answer 4

because the left experiences upwards force and right experiences downwards force

Question 5

why does this need to occur, why can’t the coil be left rotating?

Answer 5

once coil is rotated 180 degrees, current travels in opp direction so forces have also swapped direction, so coil will now turn anti-clockwise and flip to where it started, if we left it, it would keep flipping, never turns 360 degrees

Question 6

how can we fix this problem?

Answer 6

• by changing direction of current every half turn so direction of forces will always be acting clockwise so will always rotate in that direction
• use a split-ring commutator which swaps positive and negative connections every half turn, so direction of current swaps every half turn so forces acting on coil act on same direction so coil rotates in same direction all the time

Question 7

how can we increase speed of rotations?

Answer 7

• increase current
• add more turns to coil
• increase magnetic flux density, use more powerful magnets