Electricity Review Sheet
1Consider the following statements given below and determine if the charge of Object A is:
A. positive B. negative C. neutral
I. Object A is charged by friction using animal fur. Animal fur has a weaker electron affinity than object A.
II. Object A is charged by contact using a negatively charged object.
III. Object A is charged by induction using a positively charged object.
IV. Object A is attracted to a negatively charged object.
2A glass rod is given a positive charge by rubbing it with silk. The rod has become positive by
(A) losing electrons(C)losing protons
(B)gaining electrons(D)gaining protons
A
3A positively charged rod is held near the knob of a neutral electroscope. Which diagram best represents the distribution of charge on the electroscope?
D
4The diagram below represents the electric fieldsurrounding two charged spheres, A and B. What is the sign of the charge of each sphere?
(A) Sphere A is positive and sphere B is negative.
(B) Sphere A is negative and sphere B is positive.
(C) Both spheres are positive.
(D) Both spheres are negative.
B
5What is the magnitude of the electrostatic forcebetween two electrons separated by a distance of 1.00 × 10–8 meter?
(A)2.56 × 10–22N(C)2.30 × 10–12 N
(B) 2.30 × 10–20N(D)1.44 × 10–1 N
C
6A negatively charged comb has –8.0 C of charge on it. How many excess electrons are on it?
(A) 5 × 1013(C)2 × 10-14
(B)5 × 1019(D)5 × 10-25
A
7The electrical resistance of a metallic conductoris inversely proportional to its
(A)temperature(C)length
(B)cross-sectional area(D)resistivity
B
8What is the current in a 100-ohm resistorconnected to a 0.40-volt source of potentialdifference?
(A)250 mA(C)2.5 mA
(B)40 mA(D)4.0 mA
D
9The potential difference between two points in an electric field is 10 volts. The energy to move a positive charge of 2 × 10-4 C from a point at the lower potential to a point at the higher potential is:
(A)5 × 104 J(C)2 × 10-3 J
(B)2 × 10-2 J(D)2 × 10-5 J
C
10At a distance 10 cm from a point charge, the electric field is 3600 N/C and points toward the charge. The amount of this point charge is
(A)40 microcoulombs(B)4 microcoulombs
(C)4 nanocoulombs(D)4 megacoulombs
C
11The diagram to the right shows a point, P, locatedbetween two oppositely charged parallel plates. /The electric field between the plates
(A)points up, and is varying (non-uniform)
(B)points down, and is varying (non-uniform)
(C)points up, and is constant (uniform)
(D)points down, and is constant (uniform)
D
12The diagram to the right represents an electric circuit consisting of a 12-volt battery, a 3.0-ohm resistor, R1, and a variable resistor, R2. /At what value must the variable resistor be set to produce a current of 2.0 ampere through R1?
(A)6.0 Ω(C)3.0 Ω
(B)9.0 Ω(D)12 Ω
C
13An electric iron operating at 120 volts draws 10 amperes of current. How much heat energy is delivered by the iron in 30 seconds?
(A)3.0 × 102 J(C)3.6 × 103 J
(B)1.2 × 103 J(D)3.6 × 104 J
D(01/03#26)
14A 20-ohm resistor and a 30-ohm resistor are connected in parallel to a 12-volt battery as shown. As shown to the right, an ammeter is connected. /What is the equivalent resistance of the circuit?
(A)10 Ω(C)25 Ω
(B)12 Ω(D)50 Ω
B(06/04#42)
15In the previous question, what is the current reading of the ammeter?
(A)1.0 A(C)0.40 A
(B)0.60 A(D)0.20 A
B(06/04#43)
16In the previous question, what is the power of the 30-ohm resistor?
(A)4.8 W(C)30 W
(B)12 W(D)75 W
A(06/04#44)
17Two resistors are connected to a source of voltageas shown in the diagram below.
At which position should an ammeter be placedto measure the current passing only throughresistor R1 and a voltmeter be placed to measure the potential difference across R2, respectively?
(A)2 and 1(C)3 and 1
(B)3 and 2(D)4 and 1
C(01/02#38)
18Which combination of resistors has the smallest equivalent resistance?
C
Problem Solving: Do the following problems on separate paper. Show the general equation, substitutions, calculations, final results with units.
19The drawing below shows the atomic nucleus of two atoms each with 8 protons, and a nearby electron.
aFind the force between the two groups of protons.
bFind the net force on the electron.
cFind the electric field at the electron’s location.
20Two resistors are wired in series with a 12-volt battery. The first resistor has 10 volts across it, and the second resistor has 0.5 amps through it.Solve the following with equations, then check with tables:
aDraw and label the circuit schematic diagram.
bCalculate the potential difference across R2.
cCalculate the resistance R1.
dCalculate the combined resistance of R1 and R2.
eCalculate the amount of power R1 consumes.
21The schematic diagram to the right shows and ammeter A,and threeresistors.Solve the followingwith equations, then check with tables:
aCalculate resistanceR1.
bCalculate current in R2.
cCalculate current in R3.
dCalculate power in R1.
22The wiring diagram shown below shows fourlight bulbsand a battery arranged in a combination circuit. The battery is 6 volts, and each light bulb is 12 .
aDraw the schematic diagram for the circuit.
bCalculate the circuit’s equivalent resistance.
Use tables to find:
cCalculate the potential difference of each resistor.
dCalculate the current through each resistor.
eCalculate the power consumed by each resistor.
23The schematic diagram shown below shows five resistors and a battery are arranged in a combination circuit. Solve with tables.
aCalculate the equivalent resistance, total current, and total power for this circuit.
bHONORS:Calculate the current, voltage, and power of all five resistors.
24A +3.0 nanocoulumbcharge is located 1.0 m to the left of a –1.0 nanocoulumbcharge.
aDraw the field lines around these two charges.
bCalculate the electric field at the midpoint between the two charges.
cHONORS:Where should a third charge of +2 nC be placed so that it is in static equilibrium?
Answers
1 I-B, II-B, III-B, IV-A or C 2A 3D 4B 5C 6A 7B 8D 9C 10C 11D 12C 13D 14B 15B 16A 17C 18 D
19a 424 N b 5.26 N, right c 3.29 × 1019 N/C, left 20b 2 v c 20 Ω d 24 Ω e 5 W 21a 200 Ω b0.5 A c0.67 A d 72 W
22b 20Ω c VA–VD : 3.6, 1.2, 1.2, 2.4 V d IA–ID: 0.3, 0.1, 0.1, 0.2 A e PA– PD : 1.08, 0.12, 0.12, 0.48 W
23a 12 Ω, 3 A, 108 W b I1–I5: 1.8, 1.8, 1.2, 3, 3 AV1–V5 : 10.8, 7.2, 18, 12, 6 V; P1– P5 : 19.44, 12.96, 21.6, 36, 18 W
Electricity Review Sheet Solutions
1. answers: I – B, II – B, III - B, IV – A or C
I. Friction charging causes electrons to move from the animal fur to Object A, which becomes negative.
II. Conduction charging causes excess electrons in the negatively charged object to be shared with Object A, so object A becomes negatively charged.
III. Induction charging causes Object A to be oppositely charge, so using a positive object induces a negative charge on Object A.
IV. Object A can be attracted to a negatively charged object if it oppositely charged positive, but also may be attracted by polarization if it is neutral.
2. answer: A
Ordinarily only electrons can be moved from one body to another (movement of protons requires high-energy collisions in accelerators!). So a glass rod acquires a positive charge, when rubbed with silk, by losing electrons.
3. answer: D
The positively charged rod near the electroscope will attract some electrons into the knob (top) of the electroscope, leaving the electroscope polarized, but still neutral. The correct representation has negative signs in the knob, and positive signs in the leaves (bottom).
4. answer: B
By definition, electric field lines point towards negative charges and away from positive charges (because a test charge is always assumed to be positive). So sphere A must be negative and sphere B must be positive to create the field lines shown in the drawing.
5. answer: C
6. answer: A
7. answer: B
Electrical resistance depends directly on temperature, length, and resistivity. It depends inversely on cross-sectional area. That is, the wider the diameter of resistor the less the resistance (much like a drinking straw has less resistance than a narrow stirring straw.)
8. answer: D
Using the definition of resistance as the ratio of voltage divided by current:
Converting amps to milliamps:
9. answer: C
10. answer: C
11. answer: D
The electric field inside this parallel plate capacitor is constant (except at the left and right ends). The field points down because a positive test charge is used to define the direction of an electric field, and the positive test charge would be repelled by the positive charges above, and attracted by the negative charges below it.
12. answer: C
13. answer: D
14. answer: B
15. answer: B
16. answer: A
17. answer: C
The ammeter must be placed in series with resistor #1 within the branch, so at position 3. The voltmeter must be placed in parallel with resistor #2, so at position 1.
18. answer: D
19a.
19b.
19c.
20a.
20b.
20c.
20d.
20e.
table method:
R / I / V / PR1 / 4 / 0.5 / 2 / 1
R2 / 20 / 0.5 / 10 / 5
Req / 24 / 0.5 / 12 / 6
21a.
21b.
21c.
21d.
R / I / V / PR1 / 200 / 0.6 / 120 / 72
R2 / 240 / 0.5 / 120 / 60
R3 / 180 / 0.67 / 120 / 80
Req / 67.9 / 1.767 / 120 / 212
22a.
22b.
22c,d,e.
Series:
R / I / V / PRB / 12 / 0.1 / 1.2 / 0.12
RC / 12 / 0.1 / 1.2 / 0.12
RBC / 24 / 0.1 / 2.4 / 0.24
Parallel:
R / I / V / PRBC / 24 / 0.1 / 2.4 / 0.24
RD / 12 / 0.2 / 2.4 / 0.48
RBCD / 8 / 0.3 / 2.4 / 0.72
Series:
R / I / V / PRBCD / 8 / 0.3 / 2.4 / 0.72
RA / 12 / 0.3 / 3.6 / 1.08
Req / 20 / 0.3 / 6 / 1.80
23a.
23b.
Using the table method, work through each resistor column from the first table, to the second, then to the third.
Then complete the third table for the final series circuit. Only the known values are shown in bold. All others are found by multiplication or division.
Then complete the second table. Notice the bottom row is simply taken from the table below it.
Finally, complete the first table. Again, notice the bottom row is simply taken from the table below it
Series:
R / I / V / PR1 / 6 / 1.8 / 10.8 / 19.44
R2 / 4 / 1.8 / 7.2 / 12.96
R12 / 10 / 1.8 / 18 / 32.4
Parallel:
R / I / V / PR12 / 10 / 1.8 / 18 / 32.4
R3 / 15 / 1.2 / 18 / 21.6
R123 / 6 / 3 / 18 / 54
Series:
R / I / V / PR123 / 6 / 3 / 18 / 54
R4 / 4 / 3 / 12 / 36
R5 / 2 / 3 / 6 / 18
Req / 12 / 3 / 36 / 108
24a.
24b.
24c.