electromagnetism 🤪

Question 1

how to find deflection of the compass?

Answer 1

use right hand grip rule and grip a pen BUT LOOK OUT for compass above or below wire

Question 2

explanation for force experienced by current-carrying conductor

Answer 2

by Fleming’s left hand rule, where the index finger points in the direction of magnetic field and middle finger points in the direction of the current from A to B. these result in the thumb pointing to ___, in the direction of the force

Question 3

forces between two current-carrying conductors

Answer 3

conductors with current in the same direction attract, opposite direction repel

Question 4

function of a split-ring commutator

Answer 4

reverses direction of current in the coil at the vertical every half a revolution, ensuring the coil continues to rotate in the same direction

Question 5

describe how a dc motor rotates

Answer 5

using Fleming’s left hand rule, a downward force acts on AB while an upward force acts on CD. anticlockwise moment about PQ causes coil to rotate.
when the coil is in the vertical position, current is cut off because split ring commutators are not in contact with carbon brushes. the inertia of the coil carries it past vertical position

Question 6

factors affecting turning effect of coil

Answer 6

1) magnitude of current
2) number of turns of coil
3) soft iron core to concentrate magnetic field lines

Question 7

why is the speed of rotation of the coil not constant?

Answer 7

the force acting on the coil is constant, however the perpendicular distance from the pivot to the line of action of the force changes, hence turning effect on the coil changes