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## 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.