Physics 236 Practice Test #2

1) In the circuit C = 12 mF, R = 2000 W. 15 ms after the switch is closed, the voltage on the capacitor is 4.0 v. Calculate the capacitor voltage after 20 ms.

2) I1 = 24 A and I2 = 70 A. I1 is directed out of the page and I2 is directed into the page. Calculate the resultant magnetic field at a point P, directly above the midpoint of the line connecting the currents. Calculate the x and y-components and the magnitude and direction. Use x-y coordinates defined as shown.

(Ans: B = 1.60 x 10^-4 T < 69^o )

3) An 18 m length of copper wire carries a current of 12 A. The diameter of the wire is 2.8 mm and its resistivity is 1.7 x 10^-8 W m. Calculate the heat energy produced in 4.1 minutes. (Ans 1.06 x 10⁵ J)

4) An electron is accelerated through a potential difference of 28 v. It then enters a perpendicular magnetic field where it moves in a circle with a period of of 1.5 x 10^-7 s. Calculate the value of the radius of the orbit. (Ans: 7.5 cm)

5) q = 1.00 mC, v = 50.0 m/s, B = 0.020 T. Calculate F (Ans: (-0.866 j +0.500 k) mT)

6) Calculate the current in the 40 W resistor (Ans: 13.6 mA, to the right)

7) A battery with EMF = E, and internal resistance r is connected to a load resistor R. When R = 8.0 W, the power to the load is 8.0 W. When R = 18.0 W, the power is 4.5 W Calculate the emf and internal resistance. (Ans: 10 v, 2 W)