Physics 222 supplemental instruction

Class 12 Circuits October 6th, 2017

1. In the circuit below, C = 20 mF, R = 1000 , and = 100 V. The capacitor is initially uncharged and the switch is open. What is the current through the resistor 3.0 s after closing the switch?

A. 14 mAB. 34 mAC. 86 mAD. 100 mAE. 120 mA

2. In the RC circuit shown in the diagram, the switch S has been closed for a long time. After the switch is opened, how long does it take for the charge on the capacitor to decrease to 19.4 x 10-3 C?

A. 5.39 msB. 1.32 msC. 0.222 sD. 1.23 sE. 8.9 s

3. The emf and the internal resistance of a battery are as shown in the figure, Then the terminal voltage Vab is equal to 19 V, what is the current through the battery?

A. 5.3 AB. 6.0 AC. 15.5 AD. 26.0 AE. 62.0 A

4. Consider two (top and bottom) long wires in the plane of the page being 30 cm apart. The bottom wire is carrying current I1 = 10 A to the right (+x direction) and the top wire is carrying current I2 = 20 A also to the right.

A. Where in the plane of the page does the net magnetic field vanish? (Give the answer by indicating whether that’s between the wires or outside of the wires and then specify at what distance from both wires.)

A small particle of mass 2.0 g and charge 1.5 µC moves exactly in the middle between these wires to the right direction. Its initial speed is 20 m/s.

B. What’s the magnitude and direction of the magnetic force on the particle?