Physics 202 MWF 10:20 Spring 1996 (Ford)
Exam II Chapts. 28-31 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 5.00 × 10^-6 F capacitor that is initially uncharged is connected in series with a resistor R with R = 60 and an emf source with = 250 V and negligible internal resistance.

a) Just after the circuit is completed what is the potential difference v_ab across the resistor. Which point, a or b, is at higher potential?

Ans. v_ab = __250 V__

a or b? __a__


b) After time t the charge on the capacitor is 7.00 × 10 ^-4 C. At this time t what is the voltage v_ab across the resistor?

Ans. __110 V__

c) A long time after the circuit is completed what is the voltage v_ab across the resistor?

Ans. __0__


(22 pts) 2.

a) In the circuit in the sketch find the current through each resistor.

Ans. I₁ = __4 A__

I₂ = __2.67 A__

I₃ = __1.33 A__

I₄ = __3 A__

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

V_ab = __8 V__

a or b? __a__


(22 pts) 3. In the circuit shown in the sketch note that the currents through the 6 and 3 resistors are given.

a) What is the magnitude and direction (left to right or right to left) of the current through the resistor R?

Ans. I = __2 A__

direction __right to left__

b) What is the resistance R?

Ans. __5 __

c) What is the emf ?

Ans. __42 V__

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

Ans. V_ab = __-24 V__

a or b? __b__


(20 pts) 4. A particle with negative charge q = -5.0 × 10^-6 C and initial speed v₀ = 4.0 × 10³ m/s moving in the direction shown in the sketch enters a region of uniform magnetic field B = 3.0 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 = __0.060 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 = __1.2 × 10⁴ V/m__


(18 pts) 5. The rectangular loop shown in the sketch is pivoted about the y-axis and carries a current of 15.0 A in the direction indicated in the sketch. The loop is in a uniform magnetic field with magnitude 0.25 T and in the -x-direction.

a) What is the magnitude of the torque that the magnetic field exerts on the loop?

Ans. __0.0156 N·m__

b) Is the torque exerted by the magnetic field in a direction that rotates the loop toward the +x-axis or toward the +z-axis?

Ans. __+x-axis __