Download 20 Ω 60. Ω Unit 7 Lesson 1

Unit 7 Lesson 1
Exercises
1. If 2.0 A of current flow through a lightbulb for 20. minutes.
a) how many coulombs of charge (Q) have flowed thru the bulb?
b) how many electrons (N) have moved through the lamp?
(2400 C; 1.5 ×1022 electrons)
2. Find the current and direction
120 V
20 Ω
(6A, CW)
3. If this circuit is connected for 60. minutes, find
a) the current (I)
b) the total charge flow through the circuit (Q)
c) the # of electrons that have flowed through the circuit (N)
120 V
60. Ω
(2.0A, 7200C, 4.5×1022)
4. A student uses a variable voltage power supply and connects it to a lab
resistor. The student uses a voltmeter and an ammeter to measure the voltage
drop across the resistor and the current through it.
resistor
power supply
battery
cell
a) show on the diagram above how you would connect the meters to this circuit
b) plot the following data taken by the student and use it to find the resistance
of the resistor
current through resistor (amp)
voltage drop across resistor (volt)
0.00
0.0
0.80
2.0
1.90
4.0
2.70
6.0
3.70
8.0
4.50
10.0
Physics 12 Student Workbook
©Donald J. Mathewson 2002
429
5. In a house circuit, take the voltage to be 120 volts. Find the current if we
plug in
a) a 240 ohm light bulb
b) a 12 ohm hair dryer
c) a 20. ohm microwave
d) a 0.10 ohm wet finger (0.50 A; 10. A; 6.0 A; 1200 A)
6. The circuit breakers in your house are designed to 'break' the circuit if the
current gets too large. Most circuit breakers are set to 'break' or 'trip' at 15 A.
If the house voltage is 120 volts, what is the minimum resistance of an
appliance?
(8.0 Ω )
7. Why is it important to have circuit breakers (or fuses) for the circuits in our
house? Explain using relevant principles of physics.
8. Find the force (and direction) on the positive charge below.
15.0 cm
-1.00 µ C
10.0 cm
+3.00 µ C
-1.00 µ C
(3.13 N West)
9. Find the work done in moving the 2.5 µC charge from the - plate to the +
plate.
(4.4 × 10-4 J= 0.44 mJ)
175 V
+++++++++++++++++++++++++++++++++++++++++++
7.50 cm
175 V
0V
2.5 µ C
+
-------------------------------------------0V
10. Find the angle of the conical pendulum if the 2.5 kg mass completes a 2.0
metre radius circle in 1.25 seconds.(79°)
Physics 12 Student Workbook
©Donald J. Mathewson 2002
430
Unit 7 Lesson 2
Exercises
1. A 120 V source is connected to a 300. W resistor. Find
a) the current
b) the resistance
c) the heat energy produced in 20. minutes
120 V
300. W
(2.5A; 48 Ω ; 3.6×105J or 0.10 kWhr)
2. A 120. V source is connected to a 1500. W kettle. Find
a) the current
b) the resistance
c) the energy (in kWhr) used in a day
d) if energy costs 5.20 cents per kWhr, how much would it cost to run
the kettle for a day
(12.5 A; 9.60Ω ; 36.0 kWhr; $1.87)
3. A 1500 Watt kettle produces 2000. J of heat energy in 30. seconds. Find its
efficiency
(4.4%)
4. A bulb is connected to a power supply which is turned on. The current thru
the bulb is measured to be 0.450 A and the voltage is measured to be 4.40 volts.
The bulb is found to produce 1.50 J/s of light and heat energy. Find the bulb's
efficiency
( 75.8%)
5. A 220. Watt computer is connected to 110. volts of alternating current and
left on all month. Find
a) the resistance
b) current c) energy used per 30 day month
d) cost of electricity (5.50 cents/ kWhr) (55.0Ω ;2.00A; 158 kWhr; $8.71)
6. A 100.% efficient electric motor runs on 11.0A and 110. V. At what speed
could the motor pull
a)10 kg mass straight up
(12.3 m/s)
`
b) 80 kg mass up a frictionless 15° ramp (5.96 m/s)
motor
10kg
motor
80 kg
15°
7. It takes 10.0 kJ of energy to cook a hot dog. If a 30.0 ohm hot dog is connected
to 120. volts, how long will it take until it is cooked?
(20.8 sec)
Physics 12 Student Workbook
©Donald J. Mathewson 2002
436
8. Find the work done (energy required) in launching a 12 100 kg satellite
from the surface of the Earth to a circular orbit 10 200 km above the surface of
the Earth.
(6.11 × 1011 J)
9. A 1000. kg car has a maximum power output of 100. horse-power (1 hp = 746
Watt). How steep a hill can it climb at constant speed of 60. km/hr if frictional
forces add up to 500. N? (24°)
10. Find the work done and the speed after 6.00 metres of displacement
(starting from rest)
(3.00 × 102 J; 11.0 m/s)
top view, 5.00 kg
mass on frictionless
table
30.0 N
5.00 kg
40.0 N
11. A 2.00 kg pendulum (1.75 metre long) is released from a 40.0° angle
a) if there is no friction, find its speed at the bottom (2.83 m/s)
b) if its speed at the bottom is 2.20 m/s, find the energy
lost due to friction/heat energy created (3.18 J)
40.0°
released from rest
12. A cliff jumper of mass 55.0 kg jumps off a 25.0 metre high cliff. After
falling for 2.00 seconds, find (using h=0 at the bottom of the cliff)
a) the kinetic energy
(10.6 kJ=1.06 × 104J)
b) the potential energy
(2.91 kJ=2.91 × 103 J)
13. A 5.00 kg mass moving at 2.25 m/s East hits and sticks to a 8.00 kg mass
moving North at 2.00 m/s. The collision lasts 0.250 seconds. Find
a) the final speed and direction of the two masses (1.50 m/s 54.9° NofE)
b) draw a momentum vector triangle showing Pi=Pf
c) find the collision force on the 5 kg mass (37.1 N at 41.6° NofW)
14. A 10.0 kg hammer intially at rest free falls for 2.0 metres and then hits a
2.00 kg peg. Assume the peg and hammer move together freely after the
collision, and that the collision takes 0.0250 seconds. Find
a) their speed after the impact.
(5.22 m/s)
b) the collision force
(418 N)
Physics 12 Student Workbook
©Donald J. Mathewson 2002
437
Unit 7 Lesson 3
exercises: find unknown voltages and currents
1.
80 V drop
V drop =
240 V gain
60 V drop
2.
(100V)
12.5 A
2.5 A
I=
4 A
(6 A)
3.
12 V
18 V
V=
20 V
4.
(50V)
I=
1 A
2 A
(3A)
5. The three bulbs below are identical- which bulb is brightest? Explain your
answer.
i) bulb A
ii) bulb B
iii) bulb C
iv) equally bright
Note that bulb brightness depends on power, and therefore on both current
and voltage drop
A
10 V
Physics 12 Student Workbook
©Donald J. Mathewson 2002
B
C
447
6. Find unknown voltages and currents
V=
I=
100 V
V=
I=
R=50 OHM
R=
10 OHM
V=
I=
10 OHM
1A
V=
V=
I=
R=50 OHM
note: two identical resistors in
parallel will split the current evenly
(40V 2A 20 OHM; 50V 1A; 50V 1A; 10V 1A; 10V)
7. Find unknown voltages and currents
4A
V=
2A
4V
V=
I=
12 V
I=
(4A; 8V; 4V 2A)
8.Find unknown voltages and currents
6V
2A
9A
V=
(6V;
6V 3A;
6V)
4A
V=
V=
I=
9. Find unknown voltages and currents
6V
6A
I=
V=
I=
2A
V=
3V
I=
(13V 6A;
6A;
4A 4V)
4V
Physics 12 Student Workbook
©Donald J. Mathewson 2002
448
10. Find unknown voltages and currents
2V
I=
I=
V=55
I=
2A
V=
V=
10V
5A
(7A; 7A; 10V; 3A 43V; 43V)
4A
V=
11. Find unknown voltages and currents
(1A; 20V; 5V 1A;
1A 55 OHM 55V)
20 OHM
1A
V=
5 OHM
V=
I=
80 V
I=
R=
V=
I=
12. Find unknown voltages and currents
20 OHM
I=3A
V=
120 V
I=
V=
I=
R=
V=
I=2A
R=
(5A; 60 V;
60V 3A 20 OHM;
120 V 60 OHM)
13. Find unknown voltages and currents
20 OHM
V=
I=
10 OHM
I=1A
V=
5 OHM
6A
V=
15 OHM
V=
I=
note: in problesm such as
these, assume that the two
end wires are connected to
a cell. that has not been
shown
(20V 1A; 10V; 30V; 105V 7A)
Physics 12 Student Workbook
©Donald J. Mathewson 2002
449
14. What can be said about the currents I1 and I 2 if the resistance of R 2 is half
the resistance of R 1?
I2
I1
R
10 V
R/2
explain your answer using appropriate physics principles
15. What can be said about the voltage drops V1 and V2 if the resistance of R 1 is
three times the resistance of R 2?
3R
V1
V
R
V2
explain your answer using appropriate physics principles
16. What can be said about the resistances R1 and R 2 if the current through R 2
is three times the current through R 1?
10 V
I
3I
R1
R2
explain your answer using appropriate physics principles
Physics 12 Student Workbook
©Donald J. Mathewson 2002
450
Unit 7 Lesson 4
Exercises
1. Find all unknown voltages and currents(2.5 A,15V; 2.5A, 25V; 2.5 A, 20. V)
6.0 Ω
10.0 Ω
60. V
8.0 Ω
2. Find all unknown voltages and currents (6.0 A,12 V; 6.0 A, 48 V; 6.0 A,60. V)
2.0 Ω
8.0 Ω
120 V
10.0 Ω
3. Find all unknown voltages, currents and resistances
(5.0 Ω , 40. V; 8.0 A, 2.5 Ω ; 8.0 A, 40 V)
8.0 A
100. V
20. V
5.0 Ω
4. Which resistors are in series?
R1
R5
R6
R7
R8
R2
R3
R4
5) For the circuit in question 4, complete the equations:
I 3 = ___a________
V 2 = ____b___________
I 1 =__c_________
V t = V1 + V3 + _d______
I5 =
I 6 + ____e____
I 7 = ___f______
V 6 = _____g________
(a)I 4;(b) V3+V4;(c) I 2+I 3 or I 2+I 4; (d)V4; (e) I 7 or I 8; (f) I 8; (g) V7 + V8
Physics 12 Student Workbook
©Donald J. Mathewson 2002
456
6. Find all voltage drops and currents
(120 V, 12A; 120V,8.0A;120V,4.0A)
30. Ω
10. Ω
15 Ω
120
V
7. Find the total current in #6 if we
a) remove the 15 ohm
b) remove the 30. ohm
c) add another 10. ohm in parallel
d) add a 120 ohm in parallel
(16A)
(20. A)
(36 A)
(25 A)
8. Find all voltage drops and currents (120. V,0.833 A;120.V, 6.67 A; 120. V,1.67 A)
200.
Watt
100.
Watt
800.
Watt
120. V
light
blender
microwave
9.
i) In household circuit #8, find the total current if we make the
following changes to the circuit.
ii) Indicate as well if these changes would cause the circuit breaker to
trip(this happens when the total current exceeds 15.0 A)
a) adding another 100. W light (in parallel)
b) removing the 800. W microwave
c) adding a 1400. W hair dryer (in parallel)
d) adding a 300. W computer (in parallel)
(no I t =10.0 A)
(no I t =2.50 A )
(yes I t = 20.8 A)
(no I t = 11.7 A)
10. What is the maximum number of the following in a house circuit
a) 100 W light bulbs
b) 250 W TV's
b) 10 W toothbrushes
d) 800 W toasters
(18; 7;180; 2)
Physics 12 Student Workbook
©Donald J. Mathewson 2002
457
11. Which resistors are in parallel?
R1
R2
R4
R5
R6
R3
12. For the circuit in question #11, complete the equations
V5 =____a_________
V3= ____b________
Vt = V1 +_____c_____
Vt=V4 + ___d______
I4 = _______e_______
I1 = ____f_________
It= I1 +______g_____
( (a) V6 (b) V2 (c) V2 or V 3 (d) V5 or V 6 (e) I5 + I6 (f) I 2 + I3 (g) I 4 )
13. If we plug in two lights in parallel the same household circuit, one 40 W
and the other 120 W, then clearly the 120 W will be brighter.
120 W
120 W
40 W
120 v ac
120 v ac
40 W
What happens if we mistakenly hook up the 120 W and the 40 W in series?
i) the 120 W bulb is still brighter
ii) the 40 W bulb is brighter
iii) the bulbs are equally bright
14. If we add a resistor in parallel to a parallel circuit, what happens to the
total resistance?
a) it increases
b) it decreases
c) it may increase or decrease depending on the value of the resistance
we add.
Physics 12 Student Workbook
©Donald J. Mathewson 2002
458
Unit 7 Lesson 5
Exercises
1. Find R t , I t , then all voltages and currents
(30. Ω 4.0 A; 1.6 A, 24V; 2.4A, 24 V; 96V,4.0A)
15 Ω
120
V
10. Ω
24 Ω
2. Find R t , I t , then all voltages and currents
15 Ω
120
V
10. Ω
15 Ω
20. Ω
10. Ω
(20.Ω ,6.0A; 90.V,6.0A;30.V,2.0A;30.V,3.0A;20V,1.0A;10.V,1.0A)
3. Find the current through the 6.0Ω resistor
18 Ω
12 Ω
(1.3 A)
6.0 Ω
50. V
3.0 Ω
4. Find the total resistance of the circuit
(4.00Ω )
2.00 Ω
2.00 Ω
4.00 Ω
20.0 Ω
16.0 Ω
5.00 Ω
5. Find the voltage drop across the 6.00 ohm resistor
3.00 Ω
5.00 Ω
2.00 Ω
(12.6 V)
6.00 Ω
20.0 V
Physics 12 Student Workbook
©Donald J. Mathewson 2002
463
6. Find the cell voltage
(235 V)
20.0Ω
10.0 Ω
5.00 Ω
25.0Ω
3.00A
7. Find the cell voltage if 3.00A flows through the 6.00Ω resistor. (153 V)
2.00Ω
10.0 Ω
5.00 Ω
2.00Ω
3.00Ω
9.00Ω
6.00Ω
8. find the total current in this circuit when the switch(S) is
a) open
b) closed
S
10.0 Ω
20.0Ω
30.0 V
5.00 Ω
(2.00A; 2.14 A)
9. A 2.00 kg object is dropped from the top of a tree. Air resistance is negligible
a) What is the acceleration of the falling object?
(9.80m/s2)
b) what is the acceleration of the Earth?
(3.28×10-24 m/s 2)
10. If the surface below has µ=0.100, what is the acceleration of the system?
2.00 kg
12.0 kg
5.00 kg
40.0°
Physics 12 Student Workbook
©Donald J. Mathewson 2002
(0.822 m/s2)
464
Unit 7 Lesson 6
exercises
1. Find the amount of power generated by each bulb if we connect a 40. W bulb
in series with a 120. W bulb to 120. volts AC in a household circuit.
(40W bulb emits 23 W; 120W bulb emits 7.5 W)
2. Find the voltage difference between the points x and y
x
10. Ω
50. V
20. Ω
y
5.0 Ω
15 Ω
(35 V)
3. Find the voltage difference between the points x and y if 2.0 A flows though
the 3.0 Ω resistors
(320 V)
x
20.Ω
10. Ω
3.0Ω
4.0Ω
16 Ω
y
4.0Ω
2.0Ω
3.0Ω
4. Find the net voltage (Vx-Vy) for cells in series:
a) cells in same 'direction'
x
6 ohm
30V
10
ohm
60 V
y
8 ohm
b) cells opposite
x
6 ohm
30V
10
ohm
60 V
y
8 ohm
(90V; 30V)
Physics 12 Student Workbook
©Donald J. Mathewson 2002
470
5. What happens to the voltage drop across the 5Ω below when the switch is
closed? Does it increase or decrease? Explain your answer.
S
20Ω
10 Ω
5Ω
100 V
6. In the circuit below, the bulbs are identical. When we close the switch, what
happens to the brightness of the bulbs?
S
A
10 V
B
C
7. Find the current through the 3 ohm resistor. (2 A)
2Ω
4Ω
6Ω
3Ω
6Ω
12 V
Physics 12 Student Workbook
©Donald J. Mathewson 2002
471
(11.2 Ω )
8. Find the equivalent resistance
10.0 Ω
2.0 Ω
8.00 Ω
8.00 Ω
10.0 Ω
9. Find R t and I t , then all voltages and currents
(recall: equal parallel resistors split current evenly)
10 Ω
150 Ω
100 Ω
120
V
100 Ω
100 Ω
(120 Ω , 1.0 A; 10.V,1.0A; 60.V,0.60A; 60.V,0.40A; 50.V,0.50A,50.V,0.50A)
10. Find the unknown voltage drops, currents, resistances
36 V I=
R=
72 V
V=
I=
R=
2A
V=
4A
20V
R
R=
5A
V=
(6A 6 OHM
20V 10 OHM 5 OHM
16V 1A 16 OHM
16 V 3.2 OHM)
R=
11. Find the unknown voltage drops, currents, resistances
48V
4 OHM
I=
10 OHM
80V
I=
200V
I=
R=
V=
Physics 12 Student Workbook
©Donald J. Mathewson 2002
V=
I=
R=
(12A; 12A; 8A;
80V 4A 20 OHM
72V 12A 6 OHM)
I=
472
12. Electrostatics review:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Across
Down
2. Two protons will_________
1. Measured in volts per metre
5. 4 volts and 0.25 Coulomb
3. Another word for voltage
6. the charge on the electron is
4. kQ/r
________to the charge on the proton
7. kQq/r is electric ___________
8. 2 N/C and 5 C
12. force is kQq over _________
9. force times distance
13. kQq/r 2
10. the charge on the proton is called
18. force/field
the f____________ charge
19. kQq/r 2 is known as ______'s law
11. PE = 0 at __________
22. the units of potential
14. 2 J of work done on 1 C of charge
15. 2 protons and 2 neutrons form an _____particle
16. Joule/Coulomb
17. the force that holds the atom together
20. number of protons in the hydrogen nucleus
21. 10 N/C and 0.5 m
23. direction of the electric field (3 words)
Physics 12 Student Workbook
©Donald J. Mathewson 2002
473
Unit 7 Lesson 7
Exercises and Review
1. Find the terminal voltage of a 6.0 volt cell with 0.60 Ω internal resistance
that is connected to a 7.2 Ω load (5.5V)
2. Four 1.50 V cells are connected in series in the same direction inside a
flashlight. If the internal resistance of each cell is 0.400 Ω and the light bulb
has resistance 6.20 Ω then find the current through the bulb and the terminal
voltage of each cell. (0.769 A; 1.19 V)
3. A 1.5 V dry cell is short circuited and produces a maximum current of 30. A.
At this current, the terminal voltage is zero. What is the internal resistance of
the cell?
(0.050 Ω )
4. A 12.0 volt cell has 8.8 V terminal voltage when it is providing 70.A of
current. What is the internal resistance of the cell (0.045Ω )
5. A 9.0 V radio cell with internal resistance 0.20 ohm is being charged. The
charger is a 12 V cell with internal resistance 1.3 ohm. Find
a) the terminal voltage of both cells
b) the charge flow through the 9.0 V cell in 24 hrs
(9.4V; 9.4V; 170 kC=1.70×105 C)
6. Write equations relating the currents and voltage drops in the circuit
R2 V2 I2
Vt
It
R1
V1
I1
R3
V3
I3
(I t = I1 +I 2 = I1 + I3; I 2=I3; Vt =V1=V2 +V3)
7. find the total current in this circuit when the switch(S) is
a) open
b) closed
(1.9 A; 5.2 A)
S
20. V
0.50 Ω
10. Ω
5.0Ω
Physics 12 Student Workbook
©Donald J. Mathewson 2002
479
8. find the total current in this circuit when the switch(S) is
a) open
b) closed
(1.9 A; 40. A)
S
10. Ω
20. V
0.50 Ω
9. Find R t and I t then all voltages and currents
(50Ω ,2.0A; 20.V,2.0A; 20V,0.67A; 20.V,1.3A; 60.V,1.5A; 60.V,0.50 A )
10. Ω
100. V
30. Ω
15 Ω
40. Ω
120 Ω
10. Find the cell voltage given that 2.00A flows through the 15.0Ω . (225V)
4.00 Ω
4.00 Ω
5.00 Ω
3.00 Ω
10.0 Ω
14.0 Ω
15.0 Ω
11. Find the unknown voltage drops and currents
2V
I=3A
12 V
I=
4V
I=
V=
I=
(3A; 6V 3A; 3A)
12. Find the total current on a 120. volt household circuit if we plug in a
1200. W toaster and a 60.0 Watt light bulb
(10.5 A)
Physics 12 Student Workbook
©Donald J. Mathewson 2002
480
13. A 5.0 kg mass slides down a rough 25° incline at constant speed. What is the
net force acting on the mass?
(0 N)
25°
14. A satellite orbits around the equator of the Earth with a period of 30 hours.
Is it possible to move the satellite further from the Earth and keep the same
orbit period? YES or NO. Explain your answer using principles of physics
Earth
Earth
satellite
T=30 hrs
satellite
T= 30 hrs ??
15. In a wet climate, it is very difficult to build up a large charge with a
VandeGraaf generator. Why is this? Explain using principles of physics.
water
vapour
- O
H+
H+
water molecule
VdG generator
16. The cells in the circuits below are identical. Cell A has a larger terminal
voltage(V t = 1.5 volts) than cell B (Vt =1.3 volts). Which of the following is true?
a) cell A will last longer than cell B
b) cell B will last longer than cell A
c) the cells will last the same length of time
A
Vt=1.5 V
R1
B
Vt=1.3 V
R2
explain your answer using principles of physics
Physics 12 Student Workbook
©Donald J. Mathewson 2002
481
Lesson 8: Practice Exam
Section I. Multiple Choice. (1 mark each, 25 marks total)
1. The diagram shows an electrical junction and four resistors. What is
the current I 4?
2 A
4 A
I=?
3 A
a) 1A
b) 2 A
c) 3 A
d) 9 A
2. An electrical toaster is rated 1500 W at 120 V. What is its resistance?
a) 1500 Ω b) 13 Ω c) 19Ω
d) 9.6Ω
3. The emf of a dry cell is 1.50 V. When the current through it is 6.3 × 10-2 A,
the potential difference across its terminals is 1.39 V. What is the internal
resistance of the cell?
a) 2.4 Ω
b) 22Ω
c) 1.7Ω
d) 46Ω
**4,5 and 6*******************************************
15 Ω
60. Ω
20. Ω
V
A
S
4. When the switch S is closed (contact), the total resistance in the circuit is:
a) 7.5Ω
b) 30.Ω
c) 35Ω
d) 55Ω
5. When the switch S is open (no contact), the reading on the ammeter is 2.0 A.
When the switch is closed, the reading on the ammeter will
a) increase b) not change c) decrease d) double
6. When the switch is open, the ammeter reading is 2.0 A. What is the emf of
the voltage source?
a) 30. V
b) 60. V
c) 70. V
d) 110 V
*****************************************************
Physics 12 Student Workbook
©Donald J. Mathewson 2002
482
7. In the circuit shown, what happens to the ammeter and voltmeter readings
when the switch is closed? The ammeter reading __________ and
the voltmeter reading___________.
a) increases, decreases
b) decreases, increases
c) increases, increases
d) decreases, decreases
A
6V
4Ω
3Ω
S
2Ω
V
8. What is the current in the cell shown?
a) 0.17 A b) 0.50 A
c) 1.5 A
d) 2.0 A
6.0 Watt
6.0 Watt
6.0 Watt
12 V
9. A certain cell has an emf of 12.0 V and an internal resistance of 0.30 Ω . If
the cell is connected in a circuit where it delivers a current of 1.9 A, what is
the terminal voltage?
a) 0.57 V b) 11.4 V c) 12.0 V d) 12.6 V
10. If the terminal voltage of the cell in this circuit is 12.0 V and the
potential difference across R 1 is 4.6 V, what is the potential difference
across R 2?
a) 3.7 V b) 7.4 V c) 12.0 V d) it depends on the value of R1 and R 2
R1
4.6 V
R3
12.0 V
R2
Physics 12 Student Workbook
©Donald J. Mathewson 2002
483
11. In this circuit, which of the following changes would cause
the greatest increase in the current through the 6 Ω resistor?
a) removing the 2 Ω
b) removing the 4 Ω
c) connecting a 2 Ω resistor between x and y
d) connecting a 12 Ω resistor between x and y
x
6.0 Ω
12 Ω
2.0 Ω
4.0 Ω
12.0 V
y
12. If you pay 4.0 cents per kiloWatt hour, how long can you watch a 150 Watt
TV if you have 6 cents?
a) 7.5 hr
b) 0.10 hr
c) 2.5 hr
d) 10. hr
13. Find the current in resistor R4.
a) 0.091 A b) 0.12 A c) 0.14 A d) 0.18 A
R1
3.0 V
R3
33 Ω
22 Ω
12.0 V
R2
R4
66 Ω
14. What is the terminal voltage of the cell.
a) 10. V b) 12 V c) 4.0 V d) 6.0 V e) 16 V
3.0 Ω
2.0 Ω
10. V
15. A 50 V cell is connected to a 5.0 Ω resistor and a 10.0 Ω resistor in series. I f
the current in this circuit is measured using a 0.5Ω ammeter, what reading
will result?
a) 3.3 A
b) 3.2 A
c) 0.30 A
d) 2.0 A
e) 15 A
Physics 12 Student Workbook
©Donald J. Mathewson 2002
484
**16, 17***********************************
10.0 Ω
2.00 Ω
20.0 Ω
16. If 60.0 W of power is dissipated in the 20.0 Ω resistor, what is the emf of the
cell?
a) 55.4 V b) 90.0 V c) 96.0 V d) 52.0 V e) 10.7 V
17. What is the terminal voltage of the cell?
a) 58.9 V b) 53.7 V c) 94.3 V d) 52.0 V e) 92.5 V
*****************************************
18. Which picture shows an ammeter correctly reading the current through
the 2 ohm resistor?
a)
b)
2Ω
Α
2Ω
3Ω
3Ω
Α
c)
Α
d)
2Ω
2Ω
3Ω
Α
19. What is R?
a) 96 Ω b) 1.0× 102 Ω c) 56Ω
d) 150Ω
3Ω
e) 30.Ω
2.0 A
50. V
0.75 A
120 V
R
Physics 12 Student Workbook
©Donald J. Mathewson 2002
485
20. What is the total resistance of this circuit?
a) 120Ω b) 35Ω c) 10.Ω d) 30.Ω
e) 7.0 Ω
30. Ω
5.0 Ω
10. Ω
V
20. Ω
21. What is the total resistance of this circuit?
a) 19 Ω b) 4.6Ω c) 12Ω d) 2.7Ω e) 1.9 Ω
2.0 Ω
6.0 Ω
3.0 Ω
8.0 Ω
22. What current flows through the 3.0 Ω resistor?
a) 0.84 A b) 0.75 A c) 1.1 A d) 5.3 A e) 0.86 A
2.0 Ω
3.0 Ω
10. Ω
6.0 V
2.0 Ω
23. A 3.0 Ω light bulb is connected to a 6.0 volt source. The bulb produces 11
watts of heat and light energy. What is its efficiency?
a) 1.0 × 102% b) 55% c) 92% d) 61% e) 27%
Physics 12 Student Workbook
©Donald J. Mathewson 2002
486
24. Consider this circuit. What current flows through the 4.0 Ω resistor and in
what direction does it flow?
a) 4.0 A upwards b) 2.0 A downwards c) 4.0 A downwards d) 2.0 A upwards
2.0 A
6.0 Ω
1.0 Ω
8.0 Ω
4.0 Ω
V
25. For the circuit in #24, what is the cell voltage V?
a) 34 V b) 58 V c) 15 V d) 44 V e) 36 V
Section II. Problems (5 marks each, 25 marks total)
1. Make a graph, showing how the voltmeter reading will change as the
variable resistor in the circuit is decreased. What do the slope of the graph and
the y-intercept represent?
variable resistor
I
-
+
V
V
•with less resistance,more current flows
•with more current, the voltage (terminal voltage) gets smaller
(Vt=e-Ir)
• the equation of the line is
vt = (-r) I = e
•the slope is -r and so tells us the internal resistance of the
cell
•the y-intercept is the internal voltage of the cell (e)
I
Physics 12 Student Workbook
©Donald J. Mathewson 2002
487
2. Find the unknown voltage drops and currents
10 OHM
V=
I=
V=
I=
1 OHM
V=
I=
2 OHM
3A
V=
(96 V, 11A ; 90V, 9A ; 6V ; 6V, 6A ;
48 OHM
V=
I=
96V, 2A)
3. Find the voltage difference between the points x and y if 3.00 A flows
through the 2.00 Ω resistor. Indicate steps in a clear logical order. (102 volt)
x
10.0Ω
2.00Ω
5.00Ω
y
3.00Ω
6.00Ω
9.00Ω
2.00Ω
4. If a current of 2.4 A runs through a light for 7.0 minutes, how many
electrons have passed through the light? (6.3 × 10 21 electrons)
Physics 12 Student Workbook
©Donald J. Mathewson 2002
488
5. Consider the following circuit. All of the bulbs are identical
A
B
D
10 V
S
C
a) rank the bulbs in order of brightness
dimmest:
______
______
______
______
brightest
b) using principles of physics, explain your answer to a)
c) what happens to the brightness of each bulb if we close the switch S?
i) bulb A
ii) bulb B
iii) bulb C
iv) bulb D
(a) B=C< D < A;
(b) if the current through B is I, then C will have the same current. D will
have twice as much current since it has the same voltage drop as C and B
together. A will have three times as much current since it has the current of
bulb B/C and D ;
(c) the switch S shorts out D, B and C, so they all go out. This short reduces the
circuit to just bulb A. With less resistance, there is more current and so bulb A
is brighter)
1
a
2
d
3
c
4
b
5
a
6
c
7
a
8
c
9
b
10
b
16
a
17
d
18
d
19
c
20
d
21
d
22
b
23
c
24
c
25
b
Physics 12 Student Workbook
©Donald J. Mathewson 2002
11
c
12
d
13
a
14
c
15
b
489