Physics 202 MWF 10:20 Spring 1997 (Ford)

Exam II Chapts. 28-30 in SZY College Physics 7e

Show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.

(18 pts) 1. A capacitor with capacitance C that is initially uncharged is connected in series with a resistor R and an emf source with = 120 V and negligible internal resistance. Just after the circuit is completed the current in the resistor is 3.0 A. A long time after the circuit is completed the charge on the capacitor is 5 × 10^-6 C. (Note: For a capacitor, C = Q/V.)

a) What is the resistance R and the capacitance C?

Ans. R = __40 __

C = __4.17 × 10^-8 F_________________

b) At some time t after the circuit is completed the charge on the capacitor is 3 × 10^-6 C. At this instant, what is the current through the resistor?

Ans. __1.2 A__


(20 pts) 2. The circuit shown in the sketch contains two batteries, each with an emf and an internal resistance r, and two resistors.

a) What is the current I in the circuit?

Ans. __4 A__

b) What is the terminal voltage V_dc of the 12 V battery? Which point, d or c is at higher potential?

Ans. __20 V__

point __d__

c) What is the power output of the 60 V battery? (That is, what is the rate at which this battery is providing electrical energy to the rest of the circuit?)

Ans. __224 W__


(20 pts) 3. Resistors are connected to a battery as shown in the sketch.

a) What is the current through the 5 resistor?

Ans. __5.29 A__

b) What is the potential difference between points a and b? Which point, a or b, is at higher potential?

Ans. __31.8 V__

point __a__


(22 pts) 4. Consider the circuit sketched below. Note that three currents are given. Calculate:

a) the current through the 3.00 resistor.

Ans. __10 A__

b) the unknown emf's ₁ and ₂.

Ans. ₁ = __42 V__

₂ = __72 V__

c) the resistance R.

Ans. __15 __________________


(20 pts) 5. A particle with negative charge q = -5.0 × 10^-6 C and initial speed v₀ = 2.0 × 10³ m/s moving in the direction shown in the sketch enters a region of uniform magnetic field B = 2.0 T directed into the plane of the paper.

a) When the particle first enters the magnetic field region (at the point shown in the sketch), what are the magnitude and direction of the force F_B exerted on it by the magnetic field? Show the direction of this force in the sketch and clearly label your answer.

Ans. F_B = __0.020 N__

b) Calculate the magnitude and direction of the uniform electric field in the region if the particle is to pass through undeflected. Neglect gravity. Show your answer for the direction of E on the sketch and clearly label your answer.

Ans. E = __4 × 10³ V/m__