PHY 121 Final Exam Question and
answers verified to pass 2025
It would be correct to measure temperature in _______ and Heat in _______.
- correct answer ✔degrees or kelvins; calories
Assume that the volume of a container of gas is slowly decreased. Is it
possible to keep the pressure constant inside? - correct answer ✔Yes, by
slowly decreasing the temperature. Because V/T = constant. Therefore, is V
decreases T must decrease as well to maintain a constant pressure situation.
Two containers, A and B, are filled with ideal gases. The containers have a
common wall, and the temperature in A is half the temperature in B. Consider
a molecule in container A with an average kinetic energy colliding with the
common wall. Which of the following statements is true about this molecule? -
correct answer ✔The collision will result in a transfer of energy from B to A,
and the kinetic energy of the particle increases.
An ideal gas at temperature T = 100 K has an internal energy of about 2000
Joules. Which of the numbers below is the closest to the number of molecules
in the gas? - correct answer ✔9.6 × 10^23 molecules because Eth =
3/2NkBT → N = 2Eth/ 3kBT= 9.6 × 10^23 molecules.
The thermal energy of a substance - correct answer ✔is directly proportional
to its absolute (Kelvin) temperature.
Heat is - correct answer ✔the transfer of energy between two objects due to
a temperature difference.
The temperature of a volume of air is increased by 20 degrees Celsius.
Therefore - correct answer ✔the temperature increased by 20 Kelvins.
, because TF = 9/5 TC + 32 → if TC increases by 20◦ C, then TF increases by
36 ◦ F. 5
TK = TC + 273 → Degrees Celsius and Kelvins are linear.
A certain steam turbine operates with the steam (hot reservoir) at 800 K and a
condenser (cold reservoir) at 300 K. Given the choice of increasing the
efficiency by either increasing the steam temperature by 100 K or decreasing
the condenser temperature by 100 K, which option would you take? - correct
answer ✔Decrease the condenser temperature by 100 K because ηCarnot =
1− TC/Th → if decrease TC by 100 K ηCarnot = 1− 200 K/800K = 0.75 if TH
800 K
increase TH by 100 K ηCarnot = 1 − 300 K/900K = 0.67. Therefore, in terms
of efficiency it is better to decrease the temperature of the cold reservoir.
Different types of light bulbs are connected to a battery (individually, not
simultaneously). The bulb with the greatest electrical resistance will drive the -
correct answer ✔least amount of current.
A bulb is connected across a battery and the current around the circuit is
measured to be 100 amperes. How much charge travels through a cross-
section of the current-carrying wires in one minute? - correct answer ✔6000
Coulombs.
A 24 watt bulb is connected across a 12 volt battery. What is the current
through the circuit? - correct answer ✔2.0 amperes
A bulb is connected across a battery and the current around the circuit is
measured to be 3 amperes. Knowing that the difference of potential delivered
by the battery is 12 Volts, what is the resistance of the bulb? - correct answer
✔4 ohms because ∆V=IR→R=∆V/I =12V/3A =4Ω.
answers verified to pass 2025
It would be correct to measure temperature in _______ and Heat in _______.
- correct answer ✔degrees or kelvins; calories
Assume that the volume of a container of gas is slowly decreased. Is it
possible to keep the pressure constant inside? - correct answer ✔Yes, by
slowly decreasing the temperature. Because V/T = constant. Therefore, is V
decreases T must decrease as well to maintain a constant pressure situation.
Two containers, A and B, are filled with ideal gases. The containers have a
common wall, and the temperature in A is half the temperature in B. Consider
a molecule in container A with an average kinetic energy colliding with the
common wall. Which of the following statements is true about this molecule? -
correct answer ✔The collision will result in a transfer of energy from B to A,
and the kinetic energy of the particle increases.
An ideal gas at temperature T = 100 K has an internal energy of about 2000
Joules. Which of the numbers below is the closest to the number of molecules
in the gas? - correct answer ✔9.6 × 10^23 molecules because Eth =
3/2NkBT → N = 2Eth/ 3kBT= 9.6 × 10^23 molecules.
The thermal energy of a substance - correct answer ✔is directly proportional
to its absolute (Kelvin) temperature.
Heat is - correct answer ✔the transfer of energy between two objects due to
a temperature difference.
The temperature of a volume of air is increased by 20 degrees Celsius.
Therefore - correct answer ✔the temperature increased by 20 Kelvins.
, because TF = 9/5 TC + 32 → if TC increases by 20◦ C, then TF increases by
36 ◦ F. 5
TK = TC + 273 → Degrees Celsius and Kelvins are linear.
A certain steam turbine operates with the steam (hot reservoir) at 800 K and a
condenser (cold reservoir) at 300 K. Given the choice of increasing the
efficiency by either increasing the steam temperature by 100 K or decreasing
the condenser temperature by 100 K, which option would you take? - correct
answer ✔Decrease the condenser temperature by 100 K because ηCarnot =
1− TC/Th → if decrease TC by 100 K ηCarnot = 1− 200 K/800K = 0.75 if TH
800 K
increase TH by 100 K ηCarnot = 1 − 300 K/900K = 0.67. Therefore, in terms
of efficiency it is better to decrease the temperature of the cold reservoir.
Different types of light bulbs are connected to a battery (individually, not
simultaneously). The bulb with the greatest electrical resistance will drive the -
correct answer ✔least amount of current.
A bulb is connected across a battery and the current around the circuit is
measured to be 100 amperes. How much charge travels through a cross-
section of the current-carrying wires in one minute? - correct answer ✔6000
Coulombs.
A 24 watt bulb is connected across a 12 volt battery. What is the current
through the circuit? - correct answer ✔2.0 amperes
A bulb is connected across a battery and the current around the circuit is
measured to be 3 amperes. Knowing that the difference of potential delivered
by the battery is 12 Volts, what is the resistance of the bulb? - correct answer
✔4 ohms because ∆V=IR→R=∆V/I =12V/3A =4Ω.
