Download 1. An electric car is designed to run off a bank of 12

Electromagnetism & Modern Physics
Practice
PHYSICS 42 Exam 2
Name:
Rec.
1. An electric car is designed to run off a bank of 12-V batteries with total energy storage of 2 × 107 J. If
the electric motor draws 8000 W in moving the car at a steady speed of 20 m/s, how far will the car go
before it is "out of juice?"
(a)
(b)
(c)
(d)
25 km
50 km
100 km
150 km
ANSWER[
]
(4 points)
2. The following three appliances are connected to a 120 volt house circuit: i) toaster, 1200 W, ii) coffee pot,
750 W. and iii) microwave, 600 W. If all were operated at the same time what total current would they
draw?
(a)
(b)
(c)
(d)
3A
5A
10 A
21 A
ANSWER[
]
(4 points)
3. Three resistors connected in parallel have individual values of 4.0, 6.0 and 10.0 Ω, respectively. If this
combination is connected in series with a 12.0 V battery and a 2.0 Ω resistor, what is the current in the 10
2.0 Ω
Ω resistor?
(a) 0.59 A
(b) 1.0 A
12 V
4.0Ω
6.0Ω
10.0Ω
(c) 7.5 A
(d) 11.2 A
(e) 16.0 A
ANSWER[
αβγδ
]
(4 points)
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Electromagnetism & Modern Physics
Practice
PHYSICS 42 Exam 2
Name:
Rec.
The next two questions both refer to the figure below.
10 V
C
2µF
V
A
2.0 Ω
4. A 10 V emf battery is connected in series with the following: a 2 µF capacitor, a 2 Ω resistor, an ammeter,
and a switch, initially open; a voltmeter is connected in parallel across the (initially uncharged) capacitor.
At the instant the switch is closed, what are the current and capacitor voltage readings, respectively?
(a)
(b)
(c)
(d)
zero A, 10 V
zero A, zero V
5 A, zero V
5 A, 10 V
ANSWER[
]
(4 points)
5. A 10 V emf battery is connected in series with the following: a 2 microFarad capacitor, a 2 ohm resistor,
an ammeter, and a switch, initially open; a voltmeter is connected in parallel across the capacitor. After
the switch has been closed for a relatively long period (several seconds, say). What are the current and
capacitor voltage readings, respectively?
(a)
(b)
(c)
(d)
zero A, 10 V
zero A, zero V
5 A, zero V
5 A, 10 V
ANSWER[
]
(4 points)
6. A parallel plate capacitor of capacitance C0 has plates of area A with separation d between them. When it
is connected to a battery of voltage ∆V0 , it has charge of magnitude Q0 on its plates. It is then disconnected
from the battery and the plates are pulled apart to a separation 2d without discharging them. After the
plates are 2d apart, the new capacitance and the potential difference between the plates are
(a) C0 , 2∆V0
(b) 2C0 , 2∆V0
(c) 12 C0 , 21 ∆V0
(d) 21 C0 , ∆V0
(e) 21 C0 , 2∆V0
ANSWER[
αβγδ
]
(4 points)
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PHYSICS 42 Exam 2
Electromagnetism & Modern Physics
Practice
Name:
Rec.
7. A 3.0 µF capacitor is charged to a potential difference of 12.0 volts and is then disconnected from the
battery. When a second capacitor that is initially uncharged is connected in parallel with the first capacitor,
the potential difference drops to 4.0 volts.
(a) What is the capacitance of the second capacitor?
(8 points)
(b) Calculate the electrostatic energy stored in the parallel combination. Is it greater than, less than, or
the same as the energy stored on the 3.0 µF capacitor before the second capacitor was connected to
it?
(8 points)
αβγδ
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PHYSICS 42 Exam 2
Electromagnetism & Modern Physics
Practice
Name:
Rec.
8. A parallel plate capacitor with a plate area of 8.0 × 10−2 m2 and a plate separation of 1.0 × 10−4 m is
filled with polyethylene. If the potential difference between the plates is 2.0 × 104 V, what will be the
current flowing from one plate to the other through the polyethylene (ρ = 2 × 1011 Ω · m)? (10 points)
9. An ordinary light bulb draws 0.87 amps of current with connected to a 115 volt outlet. What is the
resistance of the bulb? When a series arrangement of two such bulbs is connected to the 115 volt outlet,
the current through the combination is 0.69 A. What is the resistance of each bulb now? If the resistance
is different, why is it different?
(10 points)
αβγδ
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PHYSICS 42 Exam 2
Electromagnetism & Modern Physics
Practice
Name:
Rec.
10. Four resistors, with R1 = 25 Ω, R2 = 15 Ω, R3
= 40 Ω, and R4 = 20 Ω, are connected to a 12-V
battery as shown in the figure
(a) Find the combined resistance of the four resistors.
(5 points)
(b) Find the current in each resistor
αβγδ
(15 points)
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PHYSICS 42 Exam 2
Electromagnetism & Modern Physics
Practice
11. For the circuit shown here, all the batteries are
ideal. There is no resistance anywhere that has
not been explicitly labelled. Each of the batteries
has a known emf and each resistor has a known
resistance as labelled in the accompanying figure.
The current in each battery, Ej has been labelled
as ij for j = 1,2,3. A positive value for any of these
currents means the current flows in the direction
shown. A negative sign means the current flows
opposite to the indicated arrow.
Name:
Rec.
R1 = 2!
E1= 2.0V
+
a
I2
I1
R 3 = 4!
+
R2 = 2!
+
E2= 1.0V
E3= 4.0V
I3
b
(a) Write a junction equation for the currents leaving and entering the point a.
(4 points)
(b) Write a loop equation for the currents around the left hand loop.
(4 points)
(c) Write a loop equation for the currents around the right hand loop.
(4 points)
(d) Solve the equations you derived in parts (a), (b) and (c) for each of the currents i1 , i2 , and i3
(8 points)
αβγδ
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