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Inductance and Energy

  • #1

Homework Statement



After you measure the self-inductance of a coil, you unwind it and then rewind half the length of wire into a coil with the same diameter but half the number of turns. How does this change the self-inductance?

a. It is the same.
b. It is doubled.
c. It is quadrupled.
d. It is halved.
e. It is quartered.

Homework Equations



See below.


The Attempt at a Solution



L = (N* magnetic flux)/i = (N*B*A*cos theta)/i = (n*l*A*B*cos theta)/(i), where N = n*l (l = wire length)

L2 = [(l/2)*A*(n/2)*B]/i = (1/4)*[(L*A*n*B)/i] = (1/4)*L??



Homework Statement


How much does the energy stored in an inductor change if the current through the inductor is doubled?

a. It remains the same.
b. It is doubled.
c. It is quadrupled.
d. It is halved.
e. It is quartered.




Homework Equations



See below.

The Attempt at a Solution



U = 0.5*L*I^2

U2 = 0.5*L*(2I)^2 = 4*0.5*L*I^2 = 4*U??


Homework Statement



The magnetic flux through a loop is made to vary according to the relation magnetic flux = 6t^2 + 7t + 1, where the units are SI. The emf induced in the loop when t = 2 s is

a. 38 V
b. 39 V
c. 40 V
d. 31 V
e. 19 V


Homework Equations



Emf_induced = -(d magnetic flux)/(dt)

The Attempt at a Solution



Taking the derivative, |emf| = 12t + 7, where t = 2 s

|Emf| = 12*(2s) + 7 = 31 V??

Thanks.
 

Answers and Replies

  • #2
5,428
291
You don't seem to be having any problems with this. They all look correct.
 

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