Download V Volts V q Coulombs CR Ohms Ω V Volts VP Watts

Name: _____________________________________________
Physics: Unit 5 Test Review
Period:_______Date:
Answer the following showing ALL work including equations used, substitutions with units, and correct
answer. For short answer questions, just fill in the blank.
1. How much current flows if 5.0 C of charge moves through a wire in 4.0s?
∆𝑞 0.005 𝐶
𝐼=
=
= 1.25𝐴
𝑡
4𝑠
2. The direction of conventional current is taken to be the direction in which positive charges move.
3. A(n) Volt is defined by doing one Joule of work in moving one Coulomb of charge in an electric field.
4a. 60 Joules of work is needed to move a charge of 5 C a through a wire. What potential difference will
do this work?
𝑊 60𝐽
𝑉=
=
= 12𝑉
𝑞
5𝐶
4b. What is the electric current if this charge moves through the wire over a time of 1.25 seconds?
∆𝑞
5 𝐶
=
= 4𝐴
𝑡
1.25𝑠
4c. How long will it take at this current to move 60 Coulombs of charge?
𝐼=
𝐼=
4d. What is the resistance in the circuit?
∆𝑞
∆𝑞 60 𝐶
⇒ 𝑡 =
=
= 15𝑠
𝑡
𝐼
4𝐴
𝑉 12𝑉
=
= 3Ω
𝐼
4𝐴
4e. If this resistance doubles, what will be the new electric current?
𝑅=
𝑉 12𝑉
=
= 2𝐴
𝑅
6Ω
5. What is the current flowing in a circuit operating at 120 V and has a resistance of 12 Ohms?
𝐼=
𝑉 120𝑉
=
= 10𝐴
𝑅
12Ω
6. Complete the table with proper symbols (used in an equation) SI units:
𝐼=
Symbol
SI Unit
Symbol
SI Unit Name
Electric Potential Difference
V
Volts
V
Charge
q
Coulombs
C
Electric Resistance
R
Ohms
Ω
Voltage
V
Volts
V
Electric Power
P
Watts
W
Electric Current
I
Amperes
A
Work
W
Joules
J
7a. A set of three resistors is connected to a 24.0 V battery, in series to each other: 1.0 ohm, 2.0 ohm,
and 3.0 ohm. What is the current in each resistor?
𝑅!" = 𝑅! + 𝑅! + 𝑅! … = 1Ω + 2Ω + 3Ω = 6Ω
7b. Draw a Circuit Diagram for the circuit in 7a.
8. List three ways by which objects can be charged: gain electrons, lose electrons, or induction
9. Three resistors with values of 4.0 ohms, 6.0 ohms, and 8.0 ohms, respectively, are connected in
series. What is their equivalent resistance?
𝑅!" = 𝑅! + 𝑅! + 𝑅! … = 4Ω + 6Ω + 8Ω = 18Ω
10. A light bulb has a power rating of 200.0 W at 110 V. What is the resistance of the bulb?
𝑉!
𝑉 ! (110𝑉)!
⇒ 𝑅 =
=
= 61Ω
𝑅
𝑃
200𝑊
A wire carries a steady current of 0.20A over a period of 40.0 s. What total charge moves through
wire?
∆𝑞
𝐼=
⇒ ∆𝑞 = 𝐼𝑡 = 0.20𝐴 ∗ 40.0𝑠 = 8𝐶
𝑡
Coulomb's law says that the force between any two charges depends on what 2 things? Directly on
charge magnitudes and inversely one the distance between charges
𝑃=
11.
the
12.
the
13. An electric field has magnitude and direction
14. An object that has electrons tightly bound (they don’t move) in place is known as a(n) insulator
15. When a charged cloud passes overhead, the ground below is charged by induction
16a. A set of three resistors is connected to a 24.0 V battery, in parallel to each other: 1.0 ohm, 2.0 ohm,
and 3.0 ohm. What is the equivalent resistance of the circuit?
1
1
1
1
1
1
1
1
=
+
+ … ⇒ =
+
+
= 0.55Ω
𝑅!" 𝑅! 𝑅! 𝑅!
𝑅!" 1Ω 2Ω 3Ω
16b. Draw a circuit diagram for the circuit in 16a.
17.There is a potential difference of 20.0 V across a resistor with 0.250 A of current in it. What is its
resistance?
𝑉
20𝑉
𝑅= =
= 80Ω
𝐼 0.250𝐴
18. A set of three resistors is connected to a 24.0 V battery, in parallel to each other: 1.0 ohm, 2.0 ohm,
and 3.0 ohm. How much voltage goes into each branch of the circuit?
𝑉 = 𝑉! = 𝑉! = 𝑉! … ⇒ 24𝑉 = 24𝑉 = 24𝑉 = 24𝑉
19. A set of three resistors is connected to a 24.0 V battery, in parallel to each other: 1.0 ohm, 2.0 ohm,
and 3.0 ohm. What is the current flowing through each resistor?
𝑉! 24𝑉
𝑉! 24𝑉
𝑉! 24𝑉
𝐼! =
=
= 24𝐴 𝐼! =
=
= 12𝐴 𝐼! =
=
= 8𝐴
𝑅!
1Ω
𝑅!
2Ω
𝑅!
3Ω
20. A 100-watt light bulb is connected to a 120-V outlet. How much current is in the light bulb?
𝑃 100𝑊
𝑃 = 𝑉𝐼 ⇒ 𝐼 = =
= 0.83𝐴
𝑉
120𝑉
21. A light bulb with a potential difference of 9.0 V across its filament has a power output of 80.0 W. How
much current is in the bulb filament?
𝑃 80𝑊
𝑃 = 𝑉𝐼 ⇒ 𝐼 = =
= 8.89𝐴
𝑉
9𝑉
22. What is the potential difference across a resistor that dissipates 10.0 W of power and has a current of
5.0 A?
𝑃 10.0𝑊
𝑃 = 𝑉𝐼 ⇒ 𝑉 = =
= 2.0𝑉
𝐼
5𝐴
23. For most conductors, as their temperature decreases, their resistance will INCREASE. As their length
increases, their resistance will INCREASE.
24. A 75-W light bulb and a 100-W light bulb are each connected
to a 120-V outlet. Which light bulb has more current in it?
The 100 Watt Bulb
25. A repelling force occurs between two charged objects when the charges are the same sign
26. A negatively charged rod is brought near a metal can that rests on a wood table. You touch the
opposite side of the can momentarily with your finger. The can is then charged positively
27. A light bulb has a resistance of 240 Ω when operating at 120 V. What is the current in the light bulb?
𝑃 240𝑊
𝑃 = 𝑉𝐼 ⇒ 𝐼 = =
= 2.0𝐴
𝑉
120𝑉
28. Three resistors with values of 2.0 ohms, 3.0 ohms, and 4.0 ohms, respectively, are connected in
series. What is their equivalent resistance?
𝑅!" = 𝑅! + 𝑅! + 𝑅! … = 2Ω + 3Ω + 4Ω = 9Ω
29. A device that transforms electrical energy to mechanical energy is a motor
30. A light bulb is plugged into a 120-volt outlet and has a 0.6 A current in it. What is the power rating of
the light bulb?
𝑃 = 𝑉𝐼 = 120𝑉 ∗ 0.6𝐴
31. If the potential difference across the bulb in a flashlight is 3.0 V,
what is the potential difference across the battery used to power it?
3V
32. If the current in a wire of a CD player is 0.00500 A, how long would it take for 3.00 Coulombs of
charge to pass a point in this wire?
∆𝑞
∆𝑞
3 𝐶
𝐼=
⇒ 𝑡 =
=
= 600𝑠
𝑡
𝐼
0.0050𝐴
33. Does current flow through an open circuit, or through a closed circuit? CLOSED Circuit
34. A balloon rubbed against denim gains a charge of -7.0 x 10-6 Coulombs. What is the electric force
between the balloon and the denim when the two are separated by a distance of 0.040 m?
!
∗ −7.0 × 10!! 𝐶 ∗ +7.0 × 10!! 𝐶
𝑘𝑞! 𝑞! 8.99 × 10!!∙!
!!
𝐹! =
=
= −275𝑁 𝑟!
(0.040𝑚)!
35. Draw electric field lines around the two charges below. Be sure to cover all the area around the
charges and include arrowheads. Also draw an arrow to show the direction that the positive test charge
would move: