chapter 20 - electromagnetism

Question 1

how to increase strength of magnetic field?

Answer 1

• increase the current flowing through magnetic field
• increase number of turns per unit length of the solenoid
• placing a soft iron coil within the solenoid to concentrate the field lines

Question 2

when is a magnetic effect felt

Answer 2

it is felt around a wire whenever current flows through it

Question 3

why is there a force when current flows

Answer 3

interaction between magnetic field from magnet and magnetic field created by current carrying coil results in a force which acts from the region of higher magnetic field concentration to lower magnetic field concentration

Question 4

function of carbon brushes

Answer 4

allow split ring commutator to maintain contact with circuit after it turns over to the other direction

Question 5

split ring commutator

Answer 5

allows direction of current in wire to change as it turns so that the motion of the coil can be continued

Question 6

describe how the dc motor works

Answer 6

without the split ring commutator, when the coil rotates past the vertical, the forces will not have any turning effect as both the force and the magentic field is parallel and are acting in the same direction. however, due to the coil’s momentum and inertia, it continues to rotate. however, this causes the current to reverse and the coil to rotate in the opposite direction again. however, with the addition of the split ring commutator and carbon brushes, when the coil rotates past the vertical, the commutator is able to change the direction of the current, as the brush loses contact with the commutator.

Question 7

flow of electrons

Answer 7

opposite to flow of conventional current