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Sample Final Exam
Physics 2220, Spring, 2013
D 1. An inertial reference frame S is one
a) that is identical to all other frames, inertial or not. b) in which F=ma does not hold. c) in which the
universe is spinning. d) with respect to which all other inertial reference frames move with constant
velocity but not accelerations. e) NOF (None of foregoing).
A 2. The first postulate of relativity says that in inertial reference frames:
a) all physical laws are the same. b) physical laws differ according to the reference frame. c) One must
modify all physical laws. d) Galilean transformations hold. e) NOF
B 3. The second postulate of relativity says that in inertial reference frames:
a) Light propagates. b) The vacuum speed of light always measures the same value. c) The vacuum
speed of light depends upon the relative speed of the reference frames. d) Einstein was wrong. e) NOF
D 4. A time interval in a space ship when measured by a clock on earth is:
a) Shorter. b) Longer. c) The same. d) Can't be determined. e) NOF
C 5. Consider two twins. One leaves earth on a space ship, travels near the speed of light for a period of
time, then turns around and returns to earth. After the return the one who remained on earth is:
a) younger. b) the same age. c) older. d) Their relative age cannot be determined. e) NOF
C 6. Under what circumstance is the kinetic energy of a mass moving with speed v equal to ½ mv2?
a) It is always equal to ½ mv2. b) It is never even close to ½ mv2. c) When v <<c. d) When v>>c. e)
NOF
C 7. With regard to light as a photon:
a) It is a photon unless it satisfies the photoelectric equation. b) It has a photon nature unless the
frequency is too low. c) Presumably it can always have a photon nature. d) The photon nature and the
wave nature always are observed together. e) NOF
B 8. What potential energy function best describes an oscillating O2 molecule? U=
a) -k/r. b) ½ kx2. c) mgh. d) Infinite square well. e) NOF
C 9. An infinite square well system is in a superposition state ψ=(ψ2+ψ4)/21/2 where the subscripts
indicate the n quantum numbers. If a measurement is made resulting in the observation of E4, what is the
subsequent wave function for that system immediately after the measurement?
a) (ψ2+ψ4)/21/2. b) ψ2. c) ψ4. d) ψ2/21/2. e) NOF
A 10. In the wavefunction ψ=(ψ2+ψ4)/21/2, what is the probability of measuring energy (E2+E4)/2?
a) 0. b) ½. c) 1. d) It cannot be determined. e) NOF
A 11. Which of the following particles does not possess a magnetic field?
a) Photon. b) Electron. c) Neutron. d) Proton. e) NOF
C 12. A parallel-plate capacitor with air between the plates is charged to voltage V. Then a dielectric of
constant κ= 3 is inserted fully between the plates while keeping the voltage constant. What happens to
the charge?
a) Goes down to 1/3 the original value. b) Stays the same. c) Goes up to 3 times the original value. d)
Cannot be determined. e) NOF
C 13. What is the dilemma discussed in class with regard to an electron?
a) How does it get charge? b) How does it get mass? c) How does it hold together against the huge
electrical repulsive force? d) How does it bind to a proton to form hydrogen. e) NOF
C 14. Two capacitors are connected in parallel. Which quantity is (for sure) the same for each of them?
a) C. b) Q. c) V. d) Can't be determined. e) NOF
D 15. When only is Gauss's law valid?
a) When there is sufficient symmetry. b) When the charge is inside the Gaussian surface. c) When the
charge is outside the Gaussian surface. d) It is always valid. e) NOF
A 16. SI units of electric potential are:
a) Nm/C b) J c) W/m2. d) kg m/s2. e) NOF
C 17. Why was Fletcher's name not on the original oil-drop experiment paper?
a) He didn't deserve it. b) Because he introduced oil drops instead of water drops. c) Because Millikan
wanted his own name on it alone. d) Because Fletcher didn't want it there. e) NOF
C 18. Why did Millikan and Fletcher end up using oil drops instead of water drops?
a) They hold charge more firmly. b) They are not affected by air currents. c) Because they don't
evaporate as quickly. d) Because they are less expensive. e) NOF
A 19. A USEFUL Gaussian surface is determined by
a) the symmetry of the application. b) They are all valid. c) Calculation of electric field cannot be
made. d) It looks like a loaf of bread. e) NOF
D 20. What is the current in a 2-ohm resistor having 3 volts across it?
a) 2 A. b) 3 A. c) 2/3 A. d) 3/2 A. e) NOF
A 21. A 20 H inductor develops an emf of magnitude 60 V. How long would it take to develop 30 A,
developed linearly from zero?
a) 10 s. b) 100 s. c) 4 s. d) 400 s. e) NOF
D 22. Who first discovered the law of magnetic induction but didn't publish it until another scientist beat
him to it? a) Faraday. b) Millikan. c) Fletcher. d) Henry. e) NOF
23. Suppose you double the length of a perfectly cylindrical resistor keeping the area and the material the
same and wires connected to the two ends of the cylinder. What factor will the resistance be multiplied by
a factor of:
C a) 8. b) 4. c) 2. d) ½. e) NOF
Skip 24. In an RLC circuit driven with a sinusoidal voltage in exact resonance, what will the current
approach as the resistance approaches zero?
a) Infinity. b) It will stay the same. c) zero. d) It can't be determined from the information. e) NOF
C 25. Dental x rays are developed from:
a) electrons in sinusoidal motion. b) electrons having a constant velocity. c) energetic electrons that
rapidly decelerate when they slam into a dense target. d) Rapidly accelerating photons. e) NOF
C 26. Electromagnetic whistlers are produced by
a) Puckering up and blowing. b) Oscillating electrons in a metal antenna. c) Lightning storms in the
opposite hemisphere. d) A heated oven element. e) NOF
C 27. SI units of intensity are:
a) J/s. b) N/Am2. c) W/m2. d) W/m2s.
e) NOF
C 28. The sun's electromagnetic radiation strikes two solar sails having the same area. One is black
(perfectly absorbing) and the other silvered (perfectly reflecting). The radiation force on the black one is
what factor of that on the silvered one?
a) 2. b) 1. c) ½. d) ¼. e) NOF
A 29. Assuming that the electric and magnetic fields of radiation in a vacuum are both sinusoidal, the
peak intensity is what factor times the average intensity?
a) 2. b) 21/2. c) 22. d) They are the same. e) NOF
A 30. Which of the following is NOT a way to produce a steady (non sinusoidal) magnetic field?
a) Shoot photons at a target. b) Produce a steady electric current in a wire. c) Produce a linearly
increasing (in time) uniform electric field in empty space. d) Produce a solenoid with a uniform current
in its wire. e) NOF
Skip 31. Quantum tunneling is often explained as an effect where
a) the potential is positive. b) the kinetic energy is negative. c) the force on the particle is zero. d) there
is a superposition of states. e) NOF
A 32. A space interval in a space ship when measured by a person on earth appears:
a) Shorter. b) Longer. c) The same. d) Can't be determined. e) NOF
33. If a frequency is 20 radians per second, what is the frequency in Hertz. (If you use π, you may leave
it as a symbol without plugging in the number.)
Ans: f=10/π Hz
34. An electromagnetic wave of speed 3x108m/s has a frequency of 1x1014Hz. What is the wavelength?
Ans: 3x10-6 m
35. Explain why the kinetic energy expression in the equation for the photoelectric effect is given as a
maximum value rather than simply "kinetic energy of the electron".
Ans: The most energy that can be given to the electron is that of the photon, hf, less the work function.
But that only if the particle is at the surface of the material. If the electron is deeper inside then it will
take some energy to get it to the surface. Thus the maximum.
36. Using Ampere's circuit law, calculate the magnetic field in a solenoid of radius R, length L, and
number of turns N, if the wire carries current I. Neglect edge effects.
Ans: B = µoNI/L
37. By direct substitution show that the solution to a system that is governed by the square-well
potential satisfies the Time Independent Schrodinger's Equation. Include enough detail to be convincing.
Refer to text.
38. Using Gauss's Law calculate the electric field due to a long, straight wire carrying a uniform linear
charge density λ.
Ans: E = λ/2πεor
USEFUL EQUATIONS FOR FINAL EXAM
Physics 2220, Spring, 2012
Fon 2 due to 1 = kq1q2r/r3 and
F = kq1q2er/r2
C=│Q/V │
Ex = -dV/dx
C=εoA/d
E = Fon a test charge q /q
Cparallel =C1+C2
∫E•dA =qenclosed/εo
1/Cseries =1/C1+1/C2
V=- ∫E•dr
U=CV2/2 Cwith dielectric=κCo
∮
∮
F=qE
F=quxB
j=σE
ε=IR
σ=1/ρ
j=nqv
Z=[R2+(XC-XL)2]1/2
XC=1/ωC
ωresonance =1/(LC)1/2
E = E0jsin(kx-ωt)
XL=ωL
Vrms=Vp/21/2
ω=2πf
n1sinθ1=n2sinθ2
n=c/v
ΦE
Id=ε0dΦE/dt
∫
or use sin2π(x/λ-t/T)
k=2π/λ
Plane Wave S=EB/μ0
S = ExB/μ0
ε=-LdI/dt
V=IX where X represents R , XC, XL, or Z.
Irms=Ip/21/2
B=B0ksin(kx-ωt)
c=ω/k = λ/T
E0=cB0
ε=-dФB/dt
P=I2R
R=ρL/A
f=1/T
Saverage=Speak/2
Pressure = S/c
1/s + 1/s’ = 1/f
ε=-dФB/dt
E = γmc2
γ=(1-u2/c2)-1/2
Δt = γ Δto
ΔL = ΔLo/γ
E = hf
Kmax = hf – φ
U(x)=(kx2 )/2
U=-k/r
E = mc2 + K
λ = h/p
E2=p2c2 + m2c4
ΔxΔpx ≥ (h/2π)/2
ψn=(2/L)1/2sin(nπx/L)
ΔEΔt≥(h/2π)/2
En=n2h2/(8mL2)
En=-13.6 eV/n2
ψ=(ψ1 + ψ2)/21/2