Review for Test 2

Here are some problems from last years exams:

1.(2pts each)

a) **T F
**Electrons tend to move uphill in potential.**
**

** **

b) **T F
**A charge moving along an equipotential will not experience a change
of

potential energy.

c) **T F
**Electric field lines are orthogonal to equipotential lines.

d) **T F
**When a positive charge moves along the Electric field lines its
Kinetic

Energy decreases.

e) **T F
**In a parallel plate capacitor, the capacitance is independent of the
material

between the plates.

f) **T F
**The plates of a parallel plate capacitor have an area of .004 square
meters and

are separated by a distance of .2mm so the capacitance is 177 pF.

g) **T F
**Current is defined to be the amount of charge that flows.

h) **T F
**Resistivity is proportional to conductivity.

i)
**T F
**If the charge on the plates of a capacitor doubles when a dielectric
is placed

between the plates, the dielectric constant is k = 2.

j) **T F
**The direction of a current is the same as the flow of the
electrons.

** **

1.(2pts each) Note: Some are fill in the blank.

a) **T F
**The source that converts some form of energy into electrostatic
potential

energy is a source of emf.**
**

** **

b) **T F
**A real source of emf has no internal resistance.

c) **
__________ loop rule:
**The algebraic sum of the changes in potential around a closed loop is zero

d) **
**The __________ is the time needed for the charge on a capacitor to
drop to 50%

of its initial value.

e) **T F
**No one has ever found a magnetic monopole.

f) **
**If a proton is traveling from left to right across this page and a
magnetic field

is projecting out from the page, the force acting on the proton would point

straight __________.

g) **
**The net force on a current loop in a uniform magnetic field is
____________.

h) **
_{}_____________**

i)
**T F
**The torque experienced by a current-carrying coil in a magnetic field
is used

in motors.

j) **T F
**Ohm’s law relates current and capacitance.

5.)(10pts) Find the equivalent capacitance of the figure:

2mF

2mF 3mF

3mF

2mF

12V

6.)a)(5pts) A 2mF parallel plate capacitor is connected to a 9V battery. A dielectric slab with a dielectric constant of 5 is inserted to fill the space between the plates. Find the additional charge that flows to the plates.

b)(5pts) When 12V is applied across a wire of length 200cm and radius 1mm, a current of 3mA flows through the wire. Find the resistivity of the material.

7.)(10pts) A toaster operates at 120V with a current of 8A. It takes 45sec to toast a slice of bread. At 8 cents per kilo-watt-hour, what does it cost to toast a slice of bread?

4.a)(7pts) A 2-mF capacitor is connected in parallel with a battery and a resistor. When the battery is disconnected the charge on the capacitor falls to 37% of its initial value in 3 ms. What is the resistance.

b)(8pts) In an RC charging circuit, R = 1000W, and C = 5-mF. How long will it take to charge the capacitor to 80% of its final value?