Download Sample Exam 3

Physics 2020 Exam 3 Constants and Formulae
Useful Constants
ke
= 8.99 × 109 N m2 /C2
e
= 1.60219 × 10−19 C
◦
= 8.85 × 10−12 C2 /(N m2)
µ◦
= 4π × 10−7 T m/A
h̄
= h/2π = 1.05459 × 10−34 J s
h
= 6.62620 × 10−34 J s
mp
= mH = 1.672 × 10−27 kg
me
= 9.110 × 10−31 kg
c
= 2.997925 × 108 m/s
σ
= 5.6696 × 10−8 W/m2 /K4
g
= 9.80 m/s2
1 kg
= 1000 gram
Ith
= 1.00 × 10−12 W/m2
Itp
= 1.00 W/m2
1 eV
= 1.60219 × 10−19 J
1 kHz = 103 Hz
1 km = 103 m
1 Å
= 10−10 m
1 nm
= 10−9 m
1 cm
= 10−2 m
Note that
x = log y
⇐⇒
y = 10x
x = ln y
⇐⇒
y = ex
and
where base e = 2.71828...
Useful Formulae
KE = 12 mv2
PEs = 12 kx2
2
Fe = ke |q1| |q2|/r12
PEe = ke q1 q2 /r
E = −N ∆ΦB /∆t = −L∆I/∆t
∆V = E = E` = B`v
B = µ◦ n I
n = N/`
Fs = −kx
M = vs /v
q
q
T = 1/f = 2π m/k
T = 2π L/g
β = 10 log(I/I◦)
I = P/(4πr2 )
q
v = (331.3 m/s) T /273 K = f λ
q
L = (n/2)λ
q
fn = (n/2L) F/µ (string)
v = F/µ, µ = m/L
ω = 2πf
fn = nf1
∆λ/λ◦ = (λ − λ◦ )/λ◦ = vr /c
λν = c
E = hν = hc/λ
F = σT 4
λmax = (2.897 × 10−3 m K)/T
rn = n2 (0.0529 nm)
h
i
1/λ = RAZ 2 (1/n2 ) − (1/m2 ) , (m > n)
Ln = me vn rn = nh̄
Physics 2020-001
Name:
Exam 3A – 6 April 2015
Part A: Hard Multiple Choice (10 points total, 2 points each, Circle Best Answer).
1. An electron is orbiting a proton with an angular momentum of 4.21836 × 10−34 J·s. What is
principle quantum number of the orbit of this electron?
a) 13
b) 6
c) 4
d) 2.4
e) 1
2. A spring is compressed by –2.34 cm.. If this spring contains 45.7 J of potential energy, what is
the spring constant of this spring?
a) 6.17 × 10−3 N/m
b) 8.35 N/m
d) 2.34 × 10−2 N/m
e) 1.07 × 103 N/m
c) 1.67 × 105 N/m
3. A pendulum undergoes small oscillations on the surface of the Earth. If its period of oscillation
is 1.78 s, what is the length of the pendulum?
a) 18.2 cm
b) 1.33 m
c) 8.71 m
d) 5.51 cm
e) 78.7 cm
4. A photon has a frequency of 6.682 × 1015 Hz. What is the wavelength of this photon?
a) 91.22 nm
b) 6563 Å
c) 12,420 Å
d) 12.24 nm
e) 44.87 nm
5. How fast must a 52.6 cm long metal bar move through a 2.34 T magnetic field directed in a
perpendicular direction to the velocity vector of the bar for this bar to produce an emf of 12.0 V?
a) 2.66 m/s
b) 9.75 m/s
c) 32.6 m/s
d) 3.29 cm/s
e) 32.6 cm/s
Page 2
PHYS-2020-001: General Physics II – Exam 3A – 6 April 2015
Part B: Easy Multiple Choice (10 points total, 1 point each, Circle Best Answer).
6. We observe a spectrum from a cool, low density cloud in front of a hot, opaque luminous source.
What type of spectrum would we observe from this cloud?
a) bosons
b) emission-line
d) continuous
e) absorption-line
c) fermions
7. When the Space Shuttle entered the Earth’s atmosphere, it traveled at Mach 17.3. At this
speed, the Space Shuttle is said to be traveling
a) supersonically
b) subsonically
d) at the sonic point
e) at warp speed
c) hypersonically
8. Which of the following can be interpreted as a measure of the opposition to the rate of change
of current in a circuit?
a) inductance
b) capacitance
c) emf
d) resistance
e) none of these
9. Which of the following is an example of an intrinsic property of a particle?
a) energy
b) momentum
d) acceleration
e) charge
c) position
10. Elementary particles that participate in the strong force are called
a) bosons
b) neutrinos
c) leptons
d) hadrons
e) jedi
11. What is the name of the field particle that mediates the electromagnetic force?
a) muon
b) gluon
c) weakon
d) photon
e) none of these
Page 3
PHYS-2020-001: General Physics II – Exam 3A – 6 April 2015
12. When applied to macroscopic systems, “a new physics must reduce to the old physics” is a
statement of the
a) Principle of Relativity
b) Correspondence Principle
c) Huygens’ Principle
d) Heisenberg Uncertainty Principle
e) Principle of Causality
13. For a pendulum to oscillate in simple harmonic motion, which of the following must be true?
a) The mass must be smaller than the bob-support length.
b) The pendulum must be in a gravity-free environment.
c) The bob-support tension must equal the force of gravity.
d) The angle of oscillation must be small.
e) Pendulums cannot oscillate in a simple harmonic fashion.
14. Sound waves with frequencies lower than 20 Hz are called
a) audible
b) ultrasonic
d) hypersonic
e) George
c) infrasonic
15. For sound, a change in frequency is perceived as a change in
a) density
b) pitch
c) intensity
d) pressure
e) color
PHYS-2020-001: General Physics II – Exam 3A – 6 April 2015
Page 4
Part C: Problems (20 points total, 10 points each).
16. A public speaker is talking into a bull horn. At a distance of 168 m, a spectator hears this
speaker’s voice at volume of 53.6 dB. (a) What is the intensity of the sound at this distance?
(b) What is the power of this bull horn? (See the Constants Sheet for useful information to
solve this problem. Show all work!!!)
PHYS-2020-001: General Physics II – Exam 3A – 6 April 2015
Page 5
17. You may have noticed that a bound electron (q = −e, m = me ) orbiting a proton (q = +e,
m = mp ) in the Bohr model atom obeys the following relation: 2 KEn = –PEn . (a) If an
excited electron orbits a proton at a distance of 1.9044 nm, what is the potential energy of
this electron in eV? (b) What is the orbital velocity of this electron? (Hint: You will need
to figure out the kinetic energy first from the above equation.) (c) What is the principle
quantum number of this orbit (remember that this number must be an integer)? (See the
Constants Sheet for useful information to solve this problem. Show all work and use
only the equations supplied on the equation sheet!!!)
PHYS-2020-001: General Physics II – Exam 3A – 6 April 2015
Page 6
Extra Credit Problem (5 points, do this only if you have time).
18. A guitar string 44.2 cm long and has a mass of 3.46 grams. What tension must you place
on this string to produce a third harmonic frequency of 1.44 kHz? (Show all work!)