In the figure a compass sits 1.1 cm above a wire in a circuit containing a 1.0F

Question

In the figure a compass sits 1.1 cm above a wire in a circuit containing a 1.0F capacitor charged to 4.9V, a 1.0 ohm resistor and an open switch. The compass is lined up with the earth's magnetic field. The switch closed, so that there is a current in the circuit and the switch remains closed until the capacitor is completely discharged.

a)What is magnitude of the magnetic field due to the current in the wire right after the switch is closed?

b)how does this compare with the magnitude of the field of the earth (B=5e-5T)

C)describe how the compass orientation changes right after switch is closed, and how the compass orientation changes as time goes on.

Explanation / Answer

a) I = 4.8/1 = 4.9 A
B = u/2pi I/R = 2*4.9/(1.1/100) *10^-7 = 8.9091*10^-5 T answer

b)this is larger than the magnetic field of earth by the ratio : 8.9091/5

c) when the switch is closed then the compass swings to the right due to the magnetic field from the wire. as the current decays the compass needle gradually comes back to its initial positions as shown in the diagram

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