Faraday's and Lenz's Laws

• What does Faraday's Law link together?

  Rate of change of flux linkage with e.m.f
• How is the magnitude of the induced e.m.f defined?

  It is proportional to the rate of change in magnetic flux linkage
• What does Lenz's Law describe about the direction of induced e.m.f?

  It opposes the change causing it
• What apparatus is needed to verify Lenz's Law?

  • A bar magnet
  • A coil of wire
  • A sensitive ammeter
  • No cell required
• What happens when a known pole of the bar magnet is pushed into the coil?

  A magnetic field is induced in the coil

  
• How do you determine the direction of the current in the coil?

  Using the right-hand grip rule
• What does reversing the magnet direction do to the ammeter reading?

  It gives an opposite deflection
• Why does the induced field in the coil repel the bar magnet?

  It opposes the change creating it
• What is the equation for Faraday's Law?

  ε = N Δϕ / Δt

  
• What does the equation for Faraday's Law show about the magnetic flux against time graph?

  The gradient represents the e.m.f
• What happens when a bar magnet goes through a coil?

  An e.m.f is induced due to changing magnetic flux

  
• How does the coil's magnetic field relate to the bar magnet's field?

  It acts in the opposite direction

  
• What happens to the e.m.f when a d.c. power supply is replaced with an a.c. supply?

  The e.m.f becomes alternating
• What is the angle θ between the normal to the area and the field lines?

  50°
• What are the steps to calculate the average e.m.f. induced in the coil?

  1. Identify known quantities
  2. Write Faraday's law equation
  3. Write flux linkage equation
  4. Substitute values into flux linkage equation
  5. Substitute flux linkage and time into Faraday's law
• What does the minus sign in Lenz's law signify?

  It indicates opposition to the change
• What does the term 'magnitude' of the e.m.f refer to?

  Its size, not direction