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F16 PH333 7.2.3-7.2.4
Transcript of F16 PH333 7.2.3-7.2.4
7.2.4 Energy in Magnetic Fields
Two loops of wire.
One induces a current from the B field of the other
Key equations and ideas
M is purely geometric
reverse roles of 1 and 2
now if that second loop is actually attached to the first, then we would call it self inductance.
It is measured in Henries.
Purely geometric as well... just like resistance and capacitance
Always opposed change, we call it back emf.
square lope sides a, lies midway between 2 wires 3a apart. A clockwise current I is in the little loop increasing gradually and constant( ). Find emf in big loop and direction.
When you turn up the current it creates a back emf that you have to work against. The value of work is:
or, another way you can discuss the work in a circuit as being stored in the magnetic field. Both work fine.
A source, inductor and resistor are in series long time.
Now a switch thrown and only inductor and resistor. What is current at time t, total energy to resistor, and total energy stored in inductor?
run problem backwards.
flux from the lower wire
total flux and M
initial energy stored in inductor
"Could you explain back emf i didn't quite understand it"
"Can you please help me to visualize mutual inductance verse self inductance?"
"I will probably need some more practice with Neumann formula"
"How can I tell what induced the electric current?"
"What exactly does it mean by purely geometric?"
"How is energy stored in the B field if it can't do any work?"