electromagnetism

Question 1

what happens when a large current passes through a conductor with compasses around it

Answer 1

needles of compasses deflect and form a circle around the conductor –> direction of magnetic field

Question 2

how to determine the direction of magnetic field of a conductor

Answer 2

right-hand grip rule
- thumb pointing in north pole, curl of fingers is the direction

Question 3

how does current and magnetic field affect one another

Answer 3

1. changing magnitude of current changes strength of magnetic field –> more current, stronger field
2. changing the direction of the current changes the direction of the magnetic field –> reversing, right hand grip rule
3. field is temporary –> current stops, magnetic field disappears –> temporary magnets

Question 4

distribution of magnetic field in a wire

Answer 4

1. lines near wire –> closer together, stronger
2. lines are circular and not uniformly spaced

Question 5

dot and cross in wire

Answer 5

dot = current flowing out of page
cross = current flowing into page

Question 6

how to increase the strength of magnetic field in a solenoid

Answer 6

1. increase the current flowing through the solenoid
2. increase number of turns per unit length of solenoid (coils)
3. placing a soft iron core within the solenoid

Question 7

how do electromagnets in circuit breakers work

Answer 7

normal conditions:
1. current below limit flows through coil and soft iron core becomes electromagnet but not strong enough to attract iron bolt
2. current flows normally
fault:
1. soft iron –> strong electromagnet
2. spring relaxed –> plunger pushed upwards –> open switch
- circuit breaker is switched on by depressing reset button

Question 8

why is a force produced in a current-carrying conductor

Answer 8

magnetic fields from permanent magnet and current-carrying conductor interacts, produces a force of attraction or repulsion. if force is large enough, cause a motion –> motor effect/catapult effect

Question 9

effects on force from current and magnetic field

Answer 9

1. increasing current –> larger swing/stronger force
2. increasing strength of magnetic field –> larger swing
3. reversing direction of current –> swing opposite direction
4. reverse polarity of magnet –> swing opposite direction

Question 10

which finger represents what in fleming’s left hand rule

Answer 10

index = magnetic field
middle = direction of conventional current
thumb = force

Question 11

what can you do to make the proton/electron deflect more

Answer 11

increase the field strength of the magnetic field

Question 12

why does the motor continue to turn even though there is no current every 90 degrees

Answer 12

inertia –> continue to rotate until the opposite split ring commutator comes in contact with the carbon brush

Question 13

function of split-ring commutator

Answer 13

to reverse the direction of the current in the coil every half a revolution

Question 14

what does a soft iron do to the magnetic field

Answer 14

a soft iron core concentrates the magnetic field lines and increases the strength of the magnetic field

Question 15

how can the turning effect be increased

Answer 15

1. increasing number of turns in the coil
2. increasing current
3. adding a soft iron cylinder
4. use stronger magnets

Question 16

current and attraction/replusion

Answer 16

current flowing in same direction = attract and vice versa for repel