Download Practice Exams II

Physics 203
Midterm Exam #2
Name: ______________
August 16, 2011
Makeup Exam
 Exam is closed book and closed notes. Use only formula sheet provided
 Only scientific calculator is allowed for this test.
 Write all work and answers in the papers provided.
 Show all your work and explain your reasoning (No credit will be given for
an answer that does not include the necessary solution or explanation, except
for true/false or multiple choice questions)
 Partial credit may be awarded for a correct method of solution, even if the
answer is wrong.
Part I - (5 points each) IT IS NOT NECESSARY TO SHOW YOUR WORK FOR THESE
MULTIPLE CHOICE QUESTIONS.
Choose the one correct answer for each of the following questions that best answers or completes the
question.
i)
Compared to the filament of a 100-watt light bulb, the filament of a 40-watt light bulb (of
the same material) is
a) thicker
c) same
b) thinner
d) not possible to determine without its resistivity.
ii)
A light bulb is connect by some aluminum wires to a voltage source. Compared to the
current in filament of the light bulb, the current in the aluminum wire is
a) definitely more
d) definitely less
b) sometimes more
e) not possible to determine without its resistivity.
c) often more
f) none of the above.
iii)
When a bar magnet is broken in two pieces as shown, then the magnetization of each
piece
a) is twice as strong as the original piece.
b) is half as strong as the original piece.
N
S
c) is as strong as the original piece.
d) no longer exists.
e) is a random value and have no relation to one another.
iv)
A conductor carrying a current I is placed in a magnetic field as show. If electrons are the
charge carriers of the current, which direction is the Hall field in the conductor?
a) Toward the top of the page.
b) Toward the bottom of the page.
I
c) Out of the page.
B
B
d) Into the page.
e) To the left.
f) To the right.
A positively charged particle is moving northward in a magnetic field. The magnetic
force on the particle is toward the northeast. What is the direction of the magnetic field?
a) Up
d) South
b) Down
e) Out of the page.
c) West
f) This situation can not exist.
v)
vi)
Two bulbs and a capacitor are connected to a battery as shown. Immediately after
the switch is closed, the currents are ranked as
a)
b)
c)
d)
e)
f)
I bat = IA > IC = IB
I bat > IA> IC = IB = 0
I bat = IA > and IC = IB
I bat = IA > IC = IB
I bat = IA a IC = and IB = 0
I bat = IA and IC = IB = 0
S
I bat
IA
IB
IC
C
V bat
vii)
A certain electrical quantity in a circuit is measured in units of
quantity is being measured?
a) Voltage
b) Current
c) Resistance
kg  m 2
. What electrical
C 2 .sec
d) Power
e) Magnetic Field
Part II – Questions and Problems
Please explain your reasoning or show your work clearly for each of the following
questions or problem.
1. Two wires each of length 1.5m and radius of 0.15mm are joined end to end. A potential
difference of 6.0 V is maintained across the ends of the combination. Wire 1 has a resistivity
of 1.8 106 .m and wire 2 has a resistivity of 5.6 108 .m
a) What is the current in each wire?
b) What is the potential difference across each wire?
2. Consider the circuit shown at right. Let I1 = 2.0A, I2 = 4.0A,
and I3 = 5.0A.
a) Calculate the current values of I4 and I5.
b) If 1 = 20V and Let R1= 5.find the value of R3 .
3. Suppose in the circuit shown the switch has been closed
long enough for the capacitor to be fully charged.
a)
Find the current (steady) in each resistor.
b) Find he charge on the capacitor.
c)
Now switch is opened at t = 0.
d)
What is the time constant?
How long will it take for the charge on capacitor to fall to
one-fourth of its original charge?
4. A rectangular loop of wire carries a current I and is oriented with the lower left
corner at the origin and one edge along the x-axis, as shown. A variable magnetic
field is present; its direction is into the page and its magnitude is B0 (constant value).
a) What is the total magnetic force on the loop?
b) Suppose the loop has mass m and is in a vertical plane above the ground with +y
axis upward. For what value of current  (in terms of B0, m, a, and b) will the loop
be suspended in the field?
y
b
B

I      a


x
5. Find the magnitude and direction of the magnetic field at point P. All curves are
circular arc of radius a or b.
6. A loop of wire is located inside a uniform magnetic field, as shown above. Name at
least four things you could do to induce a current in the loop.
Physics 213
Midterm Exam #2
February 18, 2004
Please enter your last name and university ID number on the optically scanned answer sheet. Fill
in the circles darkly. Also sign your name in the space provided at right. Before you begin the
exam, fill in the ID information requested on all pages of the solution papers.
Directions: The exam consists of 5 questions worth 20 points each. Only approved calculators
may be used for this exam. Palmtop or laptop computers are not allowed. A sheet of formulas
and constants is provided for your use. In solving problems, show your work and explain your
reasoning. Except for multiple choice questions, no credit will be given for an answer that does
not include the necessary solution or explanation. Partial credit may be awarded for a correct
method of solution, even if the answer is wrong. Work only on the front of the pages of the exam
booklet, and use only the exam booklet provided.
________________________________________________________________________
7. (4 points each) IT IS NOT NECESSARY TO SHOW YOUR WORK FOR THESE
MULTIPLE CHOICE QUESTIONS.
Choose the one correct answer for each of the following questions that best answers or completes
the question.
I.
The switch in the circuit is initially in the open position (as shown). After the switch is
closed, what happens to the current through the resistor?
A) It starts out at zero and gradually builds up to a maximum.
B) It suddenly rises to a maximum and gradually decreases to zero.
C) It starts out at zero and gradually builds up to a maximum and drops sharply down to
zero.
D) It remains at a constant nonzero value.
R
E) It is zero at all times.
C
V
II.
Which of the following statements is false?
A) If a uniform magnetic field acts in any direction on a rectangular current loop, the net
force on the loop will be zero.
B) If a uniform magnetic field is directed perpendicular to the plane of a rectangular
current loop, the torque on the loop will be zero.
C) When a charge particle moves through a magnetic field, its kinetic energy does not
change.
D) The drift velocity of electrons in a wire can be determined from the Hall effect.
E) The time constant  = RC is the time needed to discharge a capacitor completely.
III.
A resistor R is connected to an ideal battery V. When a second identical resistor is added
in series with the first, the total power dissipated compare with the power when only the
single resistor was present is
A) the same.
D) four time as large.
B) twice as large.
E) half as large.
C) 1/4 as large.
IV.
A 40-W light bulb and a 100-W light bulb are connected in series to a 120V source.
Which bulb will glow brighter?
A) 100-W bulb
C) both have the same brightness
B) 40-W bulb
V.
D) neither one will glow (will be lit)
Two particles enter a region of uniform magnetic field as shown. Both move at the same
speed, but particle 1 is two times as massive as particle 2. Particle 2 has 4 times the
charge of particle 1; particle 1 is positive and particle 2 is negative. Which of the
following statements is true?
A) The force on particle 1 is twice the force on particle 2.
1
2
B) Both particles are deflected in the same direction.
B
C) Particle 2 makes a tighter turn than particle 1.
D) If we double the speed of particle 1 it would
experience the same force as particle 2.
8. a) A 100-W light bulb has a thin silver filament of 0.02-mm in diameter. When it is
connected to a 120-V and turned on, its temperature rises to 750 oC. What is the length of its
filament? The resistivity of silver at 20 oC is 1.59 108 m and its temperature coefficient
 is 0.006/ oC.
b) What is the maximum number of 100-W light bulbs you can connect in parallel in 120V home circuit without tripping the 20-A circuit breaker?
9. Two 6.0-F capacitors, two 2.2-kresistors, and a 12.0-V source are connected in series.
Starting from the uncharged state, how long does it take for the current to drop from its initial
value to 1.50 mA?