magnets and magnetic fields

Question 1

temporary magnets

Answer 1

• e.g. things made or iron, steel or cobalt
• temporarily become magnets when placed in a magnet field
• stop being magnets when the field leaves

Question 2

how can you tell that a magnetic field is uniform

Answer 2

• the strengths of the fields are constant
• the distance between the poles are equal
• the spacing of field lines are equal

Question 3

what is the right hand rule

Answer 3

• used to deduce the direction of the magnetic field by using the direction of the current in the wire
• (put your thumb in the direction of the conventional current)

Question 4

solenoid

Answer 4

• a long coil of wire which has a strong even magnetic field inside but weaker outside
• inside the solenoid, the fields caused by each individual coil add up to form a strong field, but outside they cancel to give a weak field

Question 5

ways to make a wire stronger

Answer 5

• increase current
• wrap in a coil

Question 6

equation for force using magnetic field strength

Answer 6

force = field x current x length of wire in magnet

Question 7

what is a tesla

Answer 7

• 1 tesla = 1 newton per amp
• the tesla is the field strength which would exert a force of 1 newton on each 1 metre of wire carrying a current of 1 amp at right angles to the field

Question 8

what is the motor effect

Answer 8

• the force experienced when you place a current-carrying wire in a magnetic field
• this force acts perpendicular to both the direction of the current and the direction of the magnet

Question 9

Flemings left hand rule

Answer 9

• used to find the direction of a force
• make a scissor shape with your left hand
• thumb = motion
• first finger = field (N to S)
• second finger = current (+ to -)

Question 10

electromagnetic induction

Answer 10

• when magnetic field lines ‘cut’ a wire and a voltage is induced in that wire

Question 11

how to increase the strength of the induced current

Answer 11

• increasing the strength of the magnet field
• increasing the speed that the wires or magnets move at
• adding more turns to our coil

Question 12

lenz’s law

Answer 12

• the induced current will flow in a direction to try to oppose the change that caused it
• e.g. if the magnet approaches north pole first, the current in the coil will flow to create a north pole to push the magnet away

Question 13

how does a transformer work

Answer 13

• the AC goes through a primary coil, and exits the secondary coil which creates a magnetic field
• the primary and secondary coil works as an electromagnet

Question 14

what does the iron core do in a transformer

Answer 14

• it carries the magnetic field from the primary coil to the secondary coil

Question 15

what is the difference between a step up and step down transformer

Answer 15

• a step up transformer has more turns on the secondary coil and so increases voltage
• a step down transformer has fewer turns on the secondary coil and so decreases voltage

Question 16

transformer calculations

Answer 16

Ip Vp = Is Vs
I = current
V = voltage
p = primary coil
s = secondary coil