1. P5. If the current in the long straight wire is decreasing, the current induced in the coil is A. clockwise B. counter clockwise P6. If we close the switch, the current induced in the coil at the right is If after a long time we open the switch, the current induced in the coil is______

2. Transformer two coils that share the same flux
With AC currents or pulses we can easily change voltages! The iron core keeps the magnetic flux the same through both coils.

3. Transformer two coils that share the same flux
Power:
Assume no power loss

5. Tesla coil (1900)

6. Tesla coil (1900)
Capacitor stores huge amount of charge. Dump into primary in a short burst of current. Get a gigantic voltage on secondary!
tesladownunder.com

7. Inductance
How fast can we establish a current in a coil, solenoid or transformer?
Faraday’s law prevents magnetic fluxes from growing infinitely fast

8. Inductors as circuit elements
A solenoid (usually with iron core) as part of a circuit is described by its inductance L (in Henries) and is known as an inductor
Uses of inductors:
Suppress current spikes
Store energy temporarily
Generate high voltage by interrupting currents
Resonant circuit between C and L

9. Inductance
A solenoid fights the change in its flux and current!

10. Inductance
At short times\ (right when a change is attempted) L acts like an opposing battery (that later fades to zero V). Called “back emf” or “reverse voltage”, its V is exactly enough so that I can’t change instantly
At long times, L acts like a wire or “short” (because current isn’t changing then…nothing to fight)

11. It takes time to start, stop a current in an inductor

12. P1. Right after the switch is closed, which bulb is bright. A. Left B
P1. Right after the switch is closed, which bulb is bright? A. Left B. Right C. neither D. both P2. Long after the switch is closed, which bulb is bright?

13. P3. After the switch is closed, the bulb A. is bright then dims B
P3. After the switch is closed, the bulb A. is bright then dims B. is dim then brightens C. starts dim, gets bright, then dim again D. starts bright, gets dim, then bright again

14. Generating sparks (10000 V) from about 10 V
Switch
opens
periodically
the “coil”
spark plugs