Category Archives: Inductance

LR Time Constant/Variable

Demo: EM-J-LR
Pira Index: 5J 20.10

 Lab Equipment  Directions
  1.  Oscilloscope (philips)
  2. Function generator (Pasco 9598)
  3. Decade resistance (Heath EUW-30)
  4. Choke coil of thick white wire
  5. Springs
  6. BNC-DB lead (scope to resistor)
  7. BB leads
  8. 2 BA leads
  1.  Set up series as shown with either spring or the choke coil in the circuit
  2. Set the function generator to square wave, 10,000 kHZ and approx. 1/2 amplitude.
  3. Set the scope to ~0.5μs/div (for coil ~0.1μs/div) and 0.5V. Set the trigger button (/\) to negative trigger.
  4. Set the decade resistance for 10Ω. (Position 1 on the x10 knob)
Look for a trace as shown. As you stretch or compress the spring the lower part of curve should move.


Flash Emf Demo

Demo: EM-J-FE
Pira Index: 5J 10.20

 Lab Equipment  Directions
  1.  Flash-emf board
  2. Neon bulb
  3. Flashbulb
  4. Coil and core
  5. Board to elevate coil
  6. Dip needle compass
  7. 2 BB leads
Warninng: Do not stare at the flash bulb directly. Have students look at the ceiling.
  1.  With neon bulb in socket, test the circuit by pushing the switch and then letting it go. Bulb should flash when the circuit is broken due to collapsing field coil inducing a current that moves through the bulb in opposite direction.
  2. Replace neon bulb with a flash bulb.
  3. Dip needle indicates when coil is energized.
Do not test flash bulb-it has only a one time use. (use neon bulb)