# 3 physics problems concerning inductance and rlc circuit

1. Sep 29, 2005

### Pepsi24chevy

physics problems concerninginductance and rlc circuit

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1. "The resistance of a superconductor." In an experiment carried out by S. C. Collins between 1955 and 1958, a current was maintained in a superconducting lead ring for 2.50 yr with no observed loss. If the inductance of the ring was 3.14 10-8 H and the sensitivity of the experiment was 1 part in 109, what was the maximum resistance of the ring? (Suggestion: Treat this problem as a decaying current in an RL circuit and recall that e -x 1 - x for small x.)

So i have(R/L)t=10e-9 So i plug in and i get 3.98e-23 in which the program i am using says my answer is off by a magnitude of 10. I have recalculated it a few times and i get the same answer.

2.http://www.webassign.net/pse/p31-09.gif
On a printed circuit board, a relatively long straight conductor and a conducting rectangular loop lie in the same plane, as shown in Figure P31.9. Taking h = 0.600 mm, w = 1.30 mm, and L = 2.30 mm, find their mutual inductance

With this problem, the long straight conductor and the loop aren't the same shape, so i don't know how to go about solving this. I know the forumla for mutual inductance for two wires, but that is about it.

3.http://www.webassign.net/pse/p32-50.gif
[PSE6 32.P.048.] In the circuit of Figure P32.48, the battery emf is 75 V, the resistance R is 220 , and the capacitance C is 0.500 µF. The switch S is closed for a long time, and no voltage is measured across the capacitor. After the switch is opened, the potential difference across the capacitor reaches a maximum value of 150 V. What is the value of the inductance L?

FOr this problem, i don't see how to find L using angular frequency= (1/sqrt(LC)) with the variables and info i am givin. That is the only equation i can find in my book to use.

2. Sep 29, 2005

### hotvette

Can't comment on 2.

Re 1, being off by a factor of ten often means a simple mistake in decimal point, or a typo in the answer book. What program are you referring to?

Re 3, looks like a simple DC circuit. What you need to do is develop the differential equation that describes the behavior of the circuit (i.e. voltage, current, time) when the switch is closed.

3. Sep 29, 2005

### Pepsi24chevy

web assign is the program i am referring too. Also, thanks for all the help you have given me today. It has helped me out alot.

4. Sep 29, 2005

### hotvette

You are welcome.