Winter 2008 Apr. 23, 2013 PHYS 1204 Final Exam Place your name on the top of this sheet immediately.

| October 22, 2018

2008 Apr. 23, 2013
1204 Final

your name on the top of this sheet immediately.
do not open the exam until instructed to do so.

implements (pencil recommended)
(graphing or programmable OK)
X 11 in., double-sided, hand-written “cheat sheet” (hand in with exam)
night’s sleep
your wits about you

time: 2:00
time: 5:00
limit: 180 minutes
count (including this one): 8

exam consists of 10 short answer
questions and 6 long problems. Do
all. Budget your time accordingly.
Write directly on the exam. If
you need more space, ask for more paper.
Neatly cross out things that you consider incorrect rather than erasing
them. This way I can give you part marks
for them if they are, in fact, correct.

marks on exam: 70
exam counts for 25% of your final
mark in the course.

You might find it useful to know:
Electrostatic constant: K = 8.99 × 109
Permittivity of free space: ε0
= 8.85 × 10-12 C2/Nm2
Mass of proton: mp = 1.67×
10-27 kg
Fundamental charge: e = 1.60×
10-19 C
Permeability of free space:m0 = 4p× 10-7 Tm/A =
10-6 Tm/A
Acceleration due to gravity: g = 9.81
If you need a constant that isn’t given
here then please ask.

answer questions (answer 8 out of 10):
of the following questions should be answerable in a few (1-3) sentences and/or
a diagram. Point form answers are
acceptable as long as they are clear. No
calculations are required.
S1. The diagram shows wave fronts propagating
outward from two sources. Indicate the
path length differences at each of points A through D. [2 marks]

S2. For the figure in question S1 indicate below
whether each of points A through D are locations of constructive or destructive
interference. [2 marks]

constructive destructive
constructive destructive
constructive destructive
constructive destructive

.0/msohtmlclip1/01/clip_image002.gif”>S3. The diagram shows a very simple circuit. The power “in” the battery isIe
and the power “in” the resistor isI2R. A power always refers to a rate of conversion
of one form of energy to another form.
What energy conversion is occurring in the battery (from what form to
what other form)? What energy conversion
is occurring in the resistor? [2 marks]

S4. The photoelectric experiments are said to have
demonstrated the particle nature of light.
Name an observed phenomenon in the photoelectric effect experiments
which could not be explained using the wave model of light. Describe what the wave model predicted and
what was actually observed. [2 marks]


S5. The diagram shows a metal bar moving through a
region in space with a magnetic field out of the page. Which end of the bar will be the higher
potential end? Explain how you know. [2 marks]

S6. Below is a snapshot graph of two waves on a
string approaching each other. On the
axis provided sketch the snapshot of the string 2 seconds later. [2 marks]




S7. The diagram shows two charges, one positive and
the other negative.

Indicate, roughly, the direction of the electric field at point A. [1 mark]

Indicate, roughly, the direction of the force on an electron placed at point A.
[1 mark]

S8. Explain how you could charge two metal
spheres so that they have charges of exactly equal magnitude but opposite
sign. A sequence of charge diagrams
might help your explanation. [2 marks]

S9. Light of wavelength 500 nm is passed
through a diffraction grating with a distance between slits of 2100 nm. What is the maximum order (value of m) bright fringe that could be observed
with this system? Explain how you know.
[2 marks]


S10. A circuit containing a capacitor is
shown. The switch is initially open and
the capacitor is initially uncharged. Describe
what happens to the voltage difference across the capacitor after the switch is
closed. Explain. [2 marks]

Short Answer Total: /20


should be given to an appropriate number of significant figures.

.0/msohtmlclip1/01/clip_image008.gif” alt=”Text box: 1.00 cm”>.0/msohtmlclip1/01/clip_image009.gif”>.0/msohtmlclip1/01/clip_image010.gif”>P1. The diagram shows the end view of a
solenoid. The solenoid has 4000 turns
and is 10.0 cm long. Inside the solenoid
is a square “loop” of copper, 1.00 cm on a side, which has a resistance of
0.0100W. The
inside loop is not connected to a battery or other voltage source. Initially, there is a 10.0 A current in the
solenoid in the direction indicated. At
t = 2.00× 10-6
s the current starts to decrease at a uniform rate until, at 5.00× 10-6 s, the current in the
solenoid is 0 A. The current then
remains zero.

a)Find the strength of
the magnetic field (magnitude and direction) inside the solenoid initially. [3 marks]

is the initial magnetic flux through the inner loop? On the axes provided plot the magnetic flux
through the inner loop as a function of time (be sure to label the axis and
provide clear scales on the axes). [3

c)When does current
flow in the inner loop? What is the
direction of the current in the inner loop? [2 marks]

d)What is the magnitude
of the current in the inner loop? [4

P1 total: /12

.0/msohtmlclip1/01/clip_image012.gif”>P2. A wire is attached to a rigid support at one
end. The other end passes over a pulley
and has a mass suspended from it as shown.
The wire has a mass of 2.00 g.

a) If a 10.0 kg mass is suspended from
the wire then what is the wave speed on the wire? [2 marks]

b) If the wire is plucked it will
vibrate at its fundamental frequency.
What will the frequency of vibration of the wire be? [3 marks]

c) As any guitar playing physicist can
tell you, if you touch the wire lightly at its center then you force there to
be a node there (guitar players call this “playing harmonics”). What frequency will the wire vibrate at if
you touch it in the center while plucking it? [2 marks]

e) Where would you need to touch the wire
to force it to play its 3rd harmonic when plucked? [1 mark]

P2 total: /8

The diagram shows the electrical equipotential curves in some region.
a) On the diagram, sketch the electric
field lines in this region. [2 marks]

b) Use the information on the diagram
to find the electric field strength at point A. [2 marks]

c) A proton is placed at point B. What is the electrical potential energy of
the proton when it is at that point? [1

d) Suppose the proton is launched from
point B with an initial speed of 4.90× 104
m/s. It is launched in a direction
(we’re not worried about the direction in this question) such that a short time
later it passes through point C. What is
the speed of the proton as it passes through point C? [3 marks]

e) On its way from point B to point C
the proton passes through point A. What
is the magnitude of the electric force on the proton as it passes through point
A? [1 mark]

P3 total: /9


Sketch a history graph for the point at 4.00 m.
Be sure to label the axes and supply scales on the axes. [2 marks]


If the wave is represented as a sine function then what is the phase of the
wave at x = 4.00 m at t = 2.00 s? [2

Write the displacement as a function of time and position,Dy(x,
t), for this wave. Your expression
should have numerical values, including units, for all quantities except x and
t. [3 marks]

P4 total: /9

The diagram shows part of two, long, parallel
wires. The upper wire has a current of
20.0 A to the right.
a) What is the magnetic field
(magnitude and direction), due to the top wire, at the location of the bottom
wire? [3 marks]

b) Suppose we wish to magnetically
levitate the bottom wire. What direction
must the current in the bottom wire flow? [1

c) Suppose the portions of wire that
are parallel are 5.00 m long and the bottom section of wire has a mass of 5.00
g. What magnitude of current needs to
flow in the bottom wire for it to be levitated? [3 marks]

.0/msohtmlclip1/01/clip_image017.gif”>P6. In the circuit at right the switch is
initially open. We want to measure the
potential across the unknown battery but our voltmeter is broken. We know the resistance of resistor R1
to good precision from previous measurements.
We do not know the resistance of R2 to sufficient precision
to properly measure the potential across the battery. So first we’ll measure the resistance of R2.
a)With the switch open
the ammeter reads 1.00 A. What is the
resistance of resistor R2 to an appropriate precision? [2 marks]

is the potential difference across R2 when the switch is open? [1 mark]

the switch is closed the ammeter reads 1.57 A.
What is the potential difference across resistor R2 now? [1 mark]

P5/6 total: /12

is the potential difference across the unknown battery? [1 mark]

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