Current Electricity
Test Review Key
I. Matching: Match the terms and definitions
_E__ 1. Ampere
_H__ 2. Battery
_K__ 3. Potential Difference
_B__ 4. Capacitance (Pre-AP)
_M__ 5. Electric Current
_G__ 6. Capacitor
_J__ 7. Electric Circuit
_N__ 8. Schematic Diagram
_A__ 9. Dielectric (Pre-AP)
_D__ 10. Resistance
_L__ 11. Voltmeter
_F__ 12. Power
_C__ 13. Ammeter
_I__ 14. Ohmic Conductor
A. An insulator separating two plates of a capacitor.
B. The ratio of the charge on a body to its potential.
C. A device that measures the current flowing through a
point in the circuit.
D. The opposition to current flow.
E. A measure of the electric current in Coulombs per second
F. The rate at which energy is transmitted.
G. A device where electrical energy is stored.
H. An example of a voltage source.
I. A conductor which follows Ohm’s Law.
J. A continuous path through which electric current flows.
K. The difference in electric potential energy between two
points in a circuit.
L. A device that measures the potential difference across
two points in a circuit.
M. A flow of charged particles.
N. This diagram represents the components of an electric
circuit.
1. The direction of current flow in a circuit is said to be from the _positive_ terminal to the _negative_ terminal of
a battery. Charges move because of a _potential__ difference. This flow of charges is called a __current__.
2. The charges that move in a circuit are those already found in the _atoms_ of the circuit. These charges move at
a drift velocity of approximately _1 - 5__ mm/s (answers vary depending on textbook).
3. All capacitors are made of two __parallel or conducting__ plates separated by an insulator called a
_dielectric_. The two conductors have (identical / opposite) charges.
4. What 3 things are necessary to make an electric circuit and what is their function in the circuit?
Voltage source – provides the “push” or potential difference
Conductor – provides the complete path
Load – uses the electricity
5. Voltmeters are connected in _parallel_. Ammeters are connected in _series__. In the circuit below, add a
voltmeter that will tell the potential difference across the resistor and an ammeter that will tell the current
flowing through the resistor.
V
A
6. As a charge moves through resistors in a circuit, its potential energy is _reduced_. The energy used as the
charge moves around the remainder of the circuit is _equal____ to the amount of work done to give the charge
its initial energy. Therefore, the total voltage drop going around the circuit is __equal__ to the amount of
potential difference supplied by the battery.
7. Resistance is the __opposition__ to the electric current. It is also the ratio of __voltage or potential
difference__ across it to the ___current____ through it.
8. List four factors that affect the resistance of a wire and explain whether each is directly or inversely related to
the resistance of the wire.
Temperature - directly
Resistivity (nature of the material) - directly
Length - directly
Cross Sectional Area - inversely
9. To create a wire with the least resistance would be made out of a material with a (high / low) resistivity, (long /
short) length of the material, have a (large / small) diameter, and be at a (high / low) temperature.
10. To have the greatest current flow through a circuit, you want to have a (high / low) potential difference and a
(high / low) resistance. Therefore, current and voltage are (directly / inversely) related whereas current and
resistance are (directly / inversely) related.
III. Identify the Parts of a Circuit:
V
_Battery__
__resistor__
lamp or light or bulb
wire or conductor voltmeter_
A
_ammeter_
V. Solve the following problems:
1. If you have a current flowing through a resistor of 5 Amps, how many Coulombs of charge pass through the
resistor in 10 seconds? 5 = q / 10 q = 50 C
2. What is the capacitance of a capacitor with a charge of 50 microCoulombs when it is connected across a 220
V source? (Pre-AP) 50x10-6 = C(220)
C = 2.27 x 10-7 F
3. How much energy is stored in a capacitor of 50 microFarads which has been connected to 120 V? (Pre-AP)
W = 0.5 x (50x10-6)(1202) = 0.36 J
4. What is the resistance of a copper wire that is 1000 cm long and 0.81 mm in diameter at 20oC? (Resistivity
is 1.724 x10-5  mm) (Pre-AP)
A = (3.14)(0.81/2)2
R= (1.724 x10-5)(10000) / (0.515) R = 0.33 Ohms
5. A 15 Ohm resistor is connected to a 50 V battery. What is the current in the resistor?
I = 50 / 15
I = 3.3A
6. A current of 5 A flows through a 50 Ohm resistor for 2 hours. How much energy is generated?
5 = V / 50 V = 250
P = 250(5) = 1250 W
1250 = W / (20 x 60 x 60)
W = 9 x 106 J