MODERN PHYSICS (PHYS 250) (ACTUAL
EXAM) WITH CORRECT ACTUAL
QUESTIONS AND CORRECTLY WELL
DEFINED ANSWERS LATEST 2025 –2026
ALREADY GRADED A+
(July 15 Lecture)
The Principle of Relativity states only that
a. laws of mechanics are the same in all inertial frames of reference.
b. the laws of electricity and magnetism (E & M) are the same in all inertial
frames of reference.
c. both a. and b.
d. all the laws of physics are the same in all inertial frames of reference
e. all velocities are relative to the speed of light - ANSWERS-d. all the laws of
physics are the same in all inertial frames of reference
(July 15 Lecture)
,A carpenter is working on a house two blocks away. You notice a slight delay
between seeing the carpenter's hammer hit the nail and hearing the blow. At
what time does the event "hammer hits nail" occur?
a. At the instant you hear the blow.
b. At the instant you see the hammer hit
c. Very slightly before you see the hammer hit
d. Very slightly after you see the hammer hit - ANSWERS-c. Very slightly
before you see the hammer hit
(HW9) Does an electron lose energy when it tunnels? Why or why not? -
ANSWERS-An electron does not lose energy when it tunnels because energy
is conserved, and there is nowhere for the energy to go. It is easy to think
that an electron loses energy in tunneling because when you think about a
classical object penetrating a physical barrier, such as a bullet going through
an apple, in which case energy would be lost due to friction. However, friction
is a macroscopic process, and there is no dissipation in the Schrodinger
equation. Another reason you might think that an electron loses energy is
that the wave function decays exponentially
(Stop to Think 36.6)
Molly flies her rocket past Nick at constant velocity v. Molly and Nick both
measure the time it takes the rocket, from nose to tail, to pass Nick. Which of
the following is true?
a. Both Molly and Nick measure the same amount of time.
b. Molly measures a shorter time interval than Nick.
c. Nick measures a shorter time interval than Molly. - ANSWERS-c. Nick
measures proper time because Nick's clock is present at both the "nose
passes Nick" event and the "tail passes Nick" event. Proper time is the
smallest measured time interval between two events.
,(Stop to Think 36.7)
Beth and Charles are at rest relative to each other. Anjay runs past at velocity
v while holding a long pole parallel to his motion. Anjay, Beth, and Charles
each measure the length of the pole at the instant Anjay passes Beth. Rank in
order, from largest to smallest, the three lengths LA, LB, and LC. - ANSWERS-L
A > L B = L C.
Anjay measures the pole's proper length because it is at rest in his reference
frame. Proper length is the longest measured length.
Beth and Charles may see the pole differently, but they share the same
reference frame and their measurements of the length agree.
(Stop to Think 36.8)
An electron moves through the lab at 99% the speed of light. The lab
reference frame is S and the electron's reference frame is S′. In which
reference frame is the electron's rest mass larger?
a. In frame S, the lab frame
b. In frame S′, the electron's frame
c. It is the same in both frames. - ANSWERS-c. It is the same in both frames.
(May 10 Lecture): T or F. The amount of energy in each photon hitting barrel
#1 is the same as the amount in each photon hitting barrel #3. - ANSWERS-
True
The two waves have the same wavelength and hence the same frequency
(f*lamba = c). Thus E(photon) = hf is the same in both cases.
, (May 10 Lecture): T or F. The number of photons hitting barrel #1 per second
is the same as the number of photons hitting barrel #2 per second. -
ANSWERS-False
The total number of photons hitting the barrel per unit time multiplied by the
energy per photon is actually the total power delivered. These waves have
the same power but different frequency and hence different energy per
photon. Therefore, the number of photons hitting the barrels must be
different.
(May 10 Lecture): T or F. Barrel #1 and #2 heat up at the same rate. -
ANSWERS-True
The rate of heating must be proportional to the power, since this is the
energy delivered per unit time. These waves have the same power.
(May 10 Lecture): From the picture you can see that, (wavelength of #2) = 3/5
(wavelength of #1). If there are 2,500,000 photons per second hitting barrel
#2, how many photons are hitting barrel #1 per second? - ANSWERS-Power =
(number of photons(n)*energy of photon(E))/change in time(dt)
Here dt = 1 second
E = hf
We know P1 = P2
n1E1/dt = n2E2/dt
n1 = n2*(hf2/hf1) = n2*(lambda1/lambda2)
EXAM) WITH CORRECT ACTUAL
QUESTIONS AND CORRECTLY WELL
DEFINED ANSWERS LATEST 2025 –2026
ALREADY GRADED A+
(July 15 Lecture)
The Principle of Relativity states only that
a. laws of mechanics are the same in all inertial frames of reference.
b. the laws of electricity and magnetism (E & M) are the same in all inertial
frames of reference.
c. both a. and b.
d. all the laws of physics are the same in all inertial frames of reference
e. all velocities are relative to the speed of light - ANSWERS-d. all the laws of
physics are the same in all inertial frames of reference
(July 15 Lecture)
,A carpenter is working on a house two blocks away. You notice a slight delay
between seeing the carpenter's hammer hit the nail and hearing the blow. At
what time does the event "hammer hits nail" occur?
a. At the instant you hear the blow.
b. At the instant you see the hammer hit
c. Very slightly before you see the hammer hit
d. Very slightly after you see the hammer hit - ANSWERS-c. Very slightly
before you see the hammer hit
(HW9) Does an electron lose energy when it tunnels? Why or why not? -
ANSWERS-An electron does not lose energy when it tunnels because energy
is conserved, and there is nowhere for the energy to go. It is easy to think
that an electron loses energy in tunneling because when you think about a
classical object penetrating a physical barrier, such as a bullet going through
an apple, in which case energy would be lost due to friction. However, friction
is a macroscopic process, and there is no dissipation in the Schrodinger
equation. Another reason you might think that an electron loses energy is
that the wave function decays exponentially
(Stop to Think 36.6)
Molly flies her rocket past Nick at constant velocity v. Molly and Nick both
measure the time it takes the rocket, from nose to tail, to pass Nick. Which of
the following is true?
a. Both Molly and Nick measure the same amount of time.
b. Molly measures a shorter time interval than Nick.
c. Nick measures a shorter time interval than Molly. - ANSWERS-c. Nick
measures proper time because Nick's clock is present at both the "nose
passes Nick" event and the "tail passes Nick" event. Proper time is the
smallest measured time interval between two events.
,(Stop to Think 36.7)
Beth and Charles are at rest relative to each other. Anjay runs past at velocity
v while holding a long pole parallel to his motion. Anjay, Beth, and Charles
each measure the length of the pole at the instant Anjay passes Beth. Rank in
order, from largest to smallest, the three lengths LA, LB, and LC. - ANSWERS-L
A > L B = L C.
Anjay measures the pole's proper length because it is at rest in his reference
frame. Proper length is the longest measured length.
Beth and Charles may see the pole differently, but they share the same
reference frame and their measurements of the length agree.
(Stop to Think 36.8)
An electron moves through the lab at 99% the speed of light. The lab
reference frame is S and the electron's reference frame is S′. In which
reference frame is the electron's rest mass larger?
a. In frame S, the lab frame
b. In frame S′, the electron's frame
c. It is the same in both frames. - ANSWERS-c. It is the same in both frames.
(May 10 Lecture): T or F. The amount of energy in each photon hitting barrel
#1 is the same as the amount in each photon hitting barrel #3. - ANSWERS-
True
The two waves have the same wavelength and hence the same frequency
(f*lamba = c). Thus E(photon) = hf is the same in both cases.
, (May 10 Lecture): T or F. The number of photons hitting barrel #1 per second
is the same as the number of photons hitting barrel #2 per second. -
ANSWERS-False
The total number of photons hitting the barrel per unit time multiplied by the
energy per photon is actually the total power delivered. These waves have
the same power but different frequency and hence different energy per
photon. Therefore, the number of photons hitting the barrels must be
different.
(May 10 Lecture): T or F. Barrel #1 and #2 heat up at the same rate. -
ANSWERS-True
The rate of heating must be proportional to the power, since this is the
energy delivered per unit time. These waves have the same power.
(May 10 Lecture): From the picture you can see that, (wavelength of #2) = 3/5
(wavelength of #1). If there are 2,500,000 photons per second hitting barrel
#2, how many photons are hitting barrel #1 per second? - ANSWERS-Power =
(number of photons(n)*energy of photon(E))/change in time(dt)
Here dt = 1 second
E = hf
We know P1 = P2
n1E1/dt = n2E2/dt
n1 = n2*(hf2/hf1) = n2*(lambda1/lambda2)
