The Laws of Faraday & Lenz (104)
BlackBoard Notes

• Notes for Jeff:
  • Print worksheets (updated July 2025)
  • Set power supply in stockroom to 6 volts!
  • Use Uppercase Phi on board!
  • Students may not have covered this material in class, so I added new content to Board Section 2

======================= Photo - Click for a Larger Version =============================

Spring 2027: Need new photo!

======================= First Board Section =============================

• Induce current in a coil by changing the magnetic flux, Φ_B ("phi")

• Faraday's Law:

• Lenz: Direction of the induced I induces B that resists the change in Φ_B

======================= Second Board Section =============================

• (Note: Draw the following with a yellow loop and blue B vectors so that it matches our model magnet and loop!)
• Φ_B ≡ Magnetic flux
  • ⇒ The number of B vectors in a given area

Low ΦB	High ΦB

======================= Third Board Section =============================

• Galvanometer: Detects presence and direction of I

Does the needle point Left or Right?

• You Must Use the 100 kΩ Resistor Here!!

======================= Fourth Board Section =============================

• The Coil: Draw sketches on worksheet

• (Write the following on sketch! Note that bar magnet poles don't need to be drawn)
  • Draw needle pointing left or right
  • Move bar magnet halfway in or out of coil
  • Large coil
• In all cases (permanent magnet and electromagnet), what is the relationship between the change in Φ_B (increasing or decreasing) and the directions of B and B_Ind (the same or opposite)?

• Exit quiz:
  • By yourself! No notes, no compass!
  • Use Faraday & Lenz to find the north pole of an unknown bar magnet
  • Explain your reasoning!
  • Same galvanometer, different coil and connection!