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Physics 21
Practice Midterm #1 Problems
Name _____________________
Chapter 15
b 1. Doug rubs a piece of fur on a hard rubber rod, giving the rod a negative charge. What happens?
a. Protons are removed from the rod.
b. Electrons are added to the rod.
c. The fur is also charged negatively.
d. The fur is left neutral.
b 2. A repelling force must occur between two charged objects under which conditions?
a. charges are of unlike signs
b. charges are of like signs
c. charges are of equal magnitude
d. charges are of unequal magnitude
b 3.
An uncharged conductor is supported by an insulating stand. I pass a positively charged rod near the left end of
the conductor, but do not touch it. The right end of the conductor will be:
a. negative.
b. positive.
c. neutral.
d. attracted.
c 4. If body P, with a positive charge, is placed in contact with body Q (initially uncharged), what will be the nature of the
charge left on Q?
a. must be equal in magnitude to that on P
b. must be negative
c. must be positive
d. must be greater in magnitude than that on P
c 5. Four charges are at the corners of a square, with B and C on opposite
corners. Charges A and D, on the other two corners, have equal charge, while
both B and C have a charge of +1.0 C. What is the charge on A so that the force
on B is zero?
a. 1.0 C
b. 0.50 C
c. 0.35 C
d. 0.71 C
A
C
+1 Coul
B +1 Coul
D
c 6. Charge A and charge B are 3.00 m apart, and charge A is +2.00 C and charge B is +3.00 C. Charge C is located
between them at a certain point and the force on charge C is zero. How far from charge A is charge C?
a. 0.555 m
b. 0.667 m
c. 1.35 m
d. 1.50 m
c 7. An electron with a charge value of 1.6  1019 C is moving in the presence of an electric field of 400 N/C. What force
does the electron experience?
a. 2.3  1022 N
b. 1.9  1021 N
c. 6.4  1017 N
d. 4.9  1017 N
c 8. A proton initially moves left to right long the x axis at a speed of 2.00  103 m/s. It moves into an electric field, which
points in the negative x direction, and travels a distance of 0.200 m before coming to rest. If the proton's mass and
charge are 1.67  1027 kg and 1.60  1019 C respectively, what is the magnitude of the electric field?
a. 28.3 N/C
b. 13.9 N/C
c. 0.104 N/C
d. 0.038 N/C
Chapter 16
c 9.
The quantity of electrical potential, the volt, is dimensionally equivalent to:
a. force/charge.
b. force  charge.
c. electric field  distance.
d. electric field/distance.
b 10.
A free electron is in an electric field. With respect to the field, it experiences a force acting:
a. parallel.
b. anti-parallel (opposite in direction).
c. perpendicular.
d. along a constant potential line.
a 11.
In which case does an electric field do positive work on a charged particle?
a. a negative charge moves opposite to the direction of the electric field.
b. a positive charge is moved to a point of higher potential energy.
c. a positive charge completes one circular path around a stationary positive charge.
d. a positive charge completes one elliptical path around a stationary positive
charge.
a 12. If the distance between two isolated parallel plates that are oppositely charged is doubled, the electric field
between the plates is essentially unchanged. However, the:
a. potential difference between the plates will double.
b. charge on each plate will double.
c. force on a charged particle halfway between the plates will get twice as small.
d. force on a charged particle halfway between the plates will get four times as small.
c 13. If an electron is accelerated from rest through a potential difference of 1 200 V, find its
approximate velocity at the end of this process. (e = 1.6  1019 C; me = 9.1  1031 kg)
a. 1.0  107 m/s
b. 1.4  107 m/s
c. 2.1  107 m/s
d. 2.5  107 m/s
c 14. A uniform electric field, with a magnitude of 600 N/C, is directed parallel to the positive x-axis. If the potential at x
= 3.0 m is 1 000 V, what is the potential at x = 1.0 m?
a. 400 V
b. 1 600 V
c. 2 200 V
d. 2 500 V
b 15. Four point charges are on the rim of a circle of radius 10 cm. The charges are (in C) +0.50, +1.5, 1.0, 0.50. If
the electrical potential at the circle’s center due to the +0.5 charge alone is 4.5  104 V, what is the total potential at
the center due to the four charges combined?
a. 18  104 V
b. 4.5  104 V
c. zero
d. 4.5  104 V
c 16. Two point charges of values +3.4 and +6.6 C, respectively, are separated by 0.20 m. What is the potential energy
of this 2-charge system? (ke = 8.99  109 Nm2/C2)
a. +0.34 J
b. 0.75 J
c. +1.0 J
d. 3.4 J
Chapter 17
b 17. In a certain material there is a current of 16 A flowing through a surface to the right, and there is an equal amount
of positive and negative charge passing through the surface producing the current. How much negative charge passes
through the surface?
a. 8 C/s toward the right
b. 8 C/s toward the left
c. 16 C/s toward the right
d. 16 C/s toward the left
d 18.
The size of the electric current in a electrical conductor is a function of which of the following?
a. velocity of charge carriers
b. conductor cross sectional area
c. density of charge carriers
d. All of the above choices are valid.
b 19. When an electric current exists within a conducting wire, which of the following statements describes the condition
of any accompanying electric field?
a. must be zero
b. must be parallel to current flow
c. must be anti-parallel (opposite direction) to current flow
d. must be perpendicular to current flow
b 20.
The unit of electric current, the ampere, is equivalent to which of the following?
a. V
b. V/
c. m
d. V/s
b 21. A 0.20-m-long metal rod has a radius of 1.0 cm and a resistance of 3.2  105 . What is the resistivity of the
metal?
a. 1.6  108 m
b. 5.0  108 m
c. 16  108 m
d. 160  108 m
a 22. Number 10 copper wire (radius = 1.3 mm) is commonly used for electrical installations in homes. What is the
voltage drop in 40 m of #10 copper wire if it carries a current of 10 A? (The resistivity of copper is 1.7  108 m.)
a. 1.3 V
b. 0.77 V
c. 0.50 V
d. 0.13 V
a 23.
A 60-W light bulb is in a socket supplied with 120 V. What is the current in the bulb?
a. 0.50 A
b. 2.0 A
c. 60 A
d. 7 200 A
c 24.
If a 500-W heater carries a current of 4.00 A, what is the resistance of the heating element?
a. 85.7 
b. 42.8 
c. 31.3 
d. 11.2 
Chapter 18
b 25.
The basic function of an electromotive force in a circuit is to do which of the following?
a. Convert electrical energy into some other form.
b. Convert some other form of energy into electrical.
c. Both choices (a) and (b) are valid.
d. None of the above choices are valid.
a 26.
Which voltage is not caused by a source of emf?
a. the voltage across a charged capacitor
b. the voltage across two copper-iron junctions at different temperatures
c. the voltage across the terminals of a dry cell battery
d. the voltage from an electric generator
d 27. The internal resistances of an ideal voltmeter and an ideal ammeter are respectively (ideal meaning the behavior
of the system is not changed when using the meter):
a. zero and zero.
b. infinite and infinite.
c. zero and infinite.
d. infinite and zero.
c 28. When a light bulb is turned on, its resistance increases until it reaches operating temperature. What happens to
the current in the bulb as it is warming up?
a. It stays constant.
b. It increases.
c. It decreases.
d. It increases at first and then decreases.
c 29.
Three 4.0- resistors are connected in parallel to a 12.0-V battery. What is the current in any one of the resistors?
a. 16 A
b. 9.0 A
c. 3.0 A
d. 48 A
a 30. Two resistors of values 6.0 and 12.0  are connected in parallel. This combination in turn is hooked in series with
a 4.0- resistor and a 24-V battery. What is the current in the 6- resistor?
a. 2.0 A
b. 3.0 A
c. 6.0 A
d. 12 A
d 31. How much power is being dissipated by one of the 10-
resistors?
a. 24 W
b. 9.6 W
c. 16 W
d. 6.4 W
12 V
20 
2
10 
10 
c 32. Of the following choices, what is the maximum number of 60-W light bulbs you can connect in parallel in a 120V home circuit without tripping the 30-A circuit breaker?
a. 11
b. 35
c. 59
d. 3 600