Sample Exam I

Show your work! NO Electronic communication devices

Part I: Short Answer (13 points each) DO ALL THREE

1. I have a 5V battery connected to the three resistors at the right. How much total current does the battery deliver to this combination of the three resistors?

2. A resistor is made of a square bar (0.5mm×0.5mm) 2cm long. The resistance of the bar is 200W. What is the resistivity of the material?

3. When connected to a 10V battery, a capacitor stores 5×10^-4J of energy. How much energy will it store when connected to a 20V battery?

Problems: (20 points each) DO ALL THREE

4. At a point 3m from a point charge, the electric field has a magnitude of 100V/m and it points directly toward the charge. What is the electric potential there? (Be Sure to SHOW YOUR WORK!)

5. Find the electric field at P (at x = 3m on the x-axis) due to the two charges shown, -3.6mC at (x=-3m, y = 0) and +2.5mC at (x = 0, y = 4m). Find the x & y components of the total electric field and the magnitude of the total field.

6. Two charges are located at opposite corners of a rectangle as shown at the right.

a) Find the electric potential at points A and B (located at opposite corners of the rectangle).

b) How much work would the electric field do on a 200mC charge that moves from A to B?

Formulas and Expressions for Exam I

g = 10m/s² and G = 6.67x10^-11Nm²/kg²

In the figure at the right, B = C cos(J), A = C sin(J), tan(J) = A/B, and A² + B² = C².

In the figure at the right A_x = |A|cos(J) and A_y = |A|sin(J).

M_e = 9.1x10^-31kg, e = 1.6x10^-19C, M_p = 1.67x10^-27kg