- #1

davidhowie34

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## Homework Statement

1. (35 pts) You have a coop job helping to test a capacitor energy storage system. There is a rather large capacitor with capacitance, C = 2.02F. It is charged to a potential V = 602.V with the polarity of the capacitor as shown. The large, solid line on the right of the R–C circuit represents a conducting rod which is quite long. To the right of this rod, more or less in its center, there is a small square coil with N = 128 turns, and side a = 10 cm which is a distance b = 0.21 cm away from the rod.

a.) (5 pts) If the time constant of the circuit is to be 60.6 s, what should be the resistance of the resistor R1?

b.) (5 pts) How much energy will be stored on the capacitor?

c.) (5 pts) At t = 0, the switch S is closed. What will be the initial current I0?

d.) (8 pts) At the distance b = .21 cm, what is the magnetic field B at t = 35s?

e.) (8 pts) At t = 35s, what is the induced emf in the coil?

f.) (5 pts) Is the current in the coil clockwise or counter-clockwise? Explain why

[/B]

## Homework Equations

B=mu0/2a, Emf/R=I0, V/r(e^-t/RC),[/B]

## The Attempt at a Solution

a)we know that for an RC circuit, time constant is given by

tau = RC

R = tau/C

R = 60.6/2.02 = 30 Ohm

**Hence, R = 30 Ohm**

b)energy stored will be:

U = 1/2 C V^2

U = 1/2 x 2.02 x 602^2 = 366028.04 J

**Hence, U = 366028.04 J = 3.66 x 10^5 J**

c)The initial current would be:

I = V/R = 602/30 = 20.07 A

**Hence, I = 20.07 A.**

heres where it gets hard.

heres where it gets hard.

I know that the normal equation for finding magnetic field a distance away from a current source is B=u0I/2a, however, what am i to do when there is a coil at that distance? And then of course, once i figure this out, the induced emf is just the change in the flux which is BA and the direction can be found with the righthand rule. I just can't figure this one out.