4.7.2.2 Flemming's Left Hand Rule (HT only)

Question 1

Motor effect:

Answer 1

when a conductor carrying a current (e.g. conducting wire) is placed in a magnetic field the magnet producing the field and the conductor exert a force on each other - motor effect

Question 2

General motor effect question answer format:

Answer 2

• switch is closed + circuit is complete
• current flows through the circuit
• electromagnet turns on
• electromagnet has magnetic field
• the magnet attracts something iron
• something happens
• switch is opened + current is broken/incomplete
• current stops flowing through circuit
• electromagnet turns off
• iron is no longer attracted to it
• something happens

Question 3

How does an electric bell work?

Answer 3

• high voltage circuit - using switch to turn them on and off can be dangerous as you can get sparking + there is a risk of electrocution
• to turn circuits like this on and off you use a relay - relays contain 2 separate circuits
  
  • low voltage circuit containing an electromagnet - this circuit is safe to be switched on and off
  • the high voltage circuit replaced the switch with 2 metal contacts - one contact connects to a spring which keeps the contacts apart
  • have an iron block next to the spring
• low voltage circuit is turned off/switch is open so no current is flowing - the electromagnet is turned off and there is no magnetic field
• the high voltage circuit is also turned off as the contacts aren’t touching
• switch on/close switch of low voltage circuit - current now flows around the circuit
• electromagnet turns on and now a magnetic field around it
• the magnetic field attracts the iron block in the high voltage circuit
• this causes the contacts to close and switches on the high voltage circuit
• if we switch off the low voltage circuit no current so electromagnet turns off so has no magnetic field - iron block no longer attracted to it
• the contacts spring apart and the high voltage circuit is switched off

Question 4

How does a door bell work?

Answer 4

• the switch is closed when the buzzer is pressed
• causes current to flow through the circuit causing electromagnet to turn on
• magnetic field produced by the electromagnet
• iron contact now attracted towards the magnetic field
• when the contact moves towards the magnetic field the clapper now hits the bell
• at the same time, this breaks the circuit
• now no current flowing so no magnetic field
• the iron contact springs back to its original position
• now circuit is complete again so current flows around the circuit and the process is repeated

Question 5

How does the motor effect work?

Answer 5

• place conducting wire with a current through it into a magnetic field
• the magnetic field around the wire interacts with the magnetic field between the magnets
• this means thats the wire now experiences a force - upwards direction

Question 6

Calculate the force for a conductor at right angle to a magnetic field carrying a current:

Answer 6

Question 7

Flemming’s left hand rule:

Answer 7

• thumb - movement, motion, direction of force
• first finger field - N to S
• second finger - current +ve to -ve

Question 8

What happens if the conductor or conducting wire is parallel to the magnetic field?

Answer 8

if the conductor/conducting wire is parallel to the magnetic field then it will not experience a force

Question 9

What factors affect the size of the force on the conductor?

Answer 9

• Current - larger the current, the larger the force
• Length - the longer the length of the conductor, the larger the force
• Magnetic Flux Density - the higher the density, the more magnetic field lines and the larger the force on the conductor
  
  • increase strength of magnet - more magnets