Deck 4: Heat, the Laws of Thermodynamics, Electric Charges, Forces, and Fields

Question 1

A 24.0 kg sample of ice is at 0.00°C. How much heat is needed to melt it?
(For water L_f = 334 kJ/kg and L_v = 2257 kJ/kg.)

A) 8.02 × 10³ _kJ
B) 2.19 × 10⁶ _kJ
C) 0.00 kJ
D) 5.42 × 10⁴ _kJ

Answer 1

8.02 × 10³ _kJ

Question 2

Which of the following is a true statement?

A) Several days after a snowstorm, the roof on Jones's house is uniformly covered with snow, whereas on Smith's house next door the snow has completely melted off. A likely reason for this is that Smith's house has better roof insulation than does Jones's.
B) When you get out of a swimming pool and stand dripping wet in a breeze you feel colder than you would if your skin were dry. This is a purely psychological effect, since measurement of your skin temperature would yield the same value in both cases, wet or dry.
C) In some regions the following sign is frequently seen as one approaches a bridge: "CAUTION: BRIDGE MAY BE ICY." One reason you might expect a bridge to be icier than the road leading up to it is that the bridge has both its top and bottom exposed to cold air, whereas only the top surface of the road is in contact with cold air.
D) When the metal cooling coils in a freezer become coated with ice this helps the freezer more effectively remove heat from warm foods placed in the freezer.
E) Thermos bottles have a vacuum between the inner and outer layers of glass in order to reduce heat transfer due to radiation, since radiation cannot travel through a vacuum.

Answer 2

In some regions the following sign is frequently seen as one approaches a bridge: "CAUTION: BRIDGE MAY BE ICY." One reason you might expect a bridge to be icier than the road leading up to it is that the bridge has both its top and bottom exposed to cold air, whereas only the top surface of the road is in contact with cold air.

Question 3

In years of heavy snow pack in the mountains it is sometimes desirable to induce early melting of the snow, rather than wait until it all melts suddenly and causes floods. It has been suggested that a way to accomplish this might be to have planes fly over the snow fields and sprinkle them with black soot. What do you think of this idea? Would it work?

A) Yes, it would probably work because the black surface would be a better absorber of sunlight than would the white snow.
B) Yes, it would work because the soot would raise the melting point of the snow.
C) Yes, it would work because the soot would decrease the specific heat capacity of the snow.
D) No, it would not work because it is infrared radiation and not visible radiation which melts the snow.
E) No, it would not work because sunlight has very little effect on how fast the snow melts.

Answer 3

Yes, it would probably work because the black surface would be a better absorber of sunlight than would the white snow.

Question 4

At higher altitudes it takes __________ time to bring water to a boil on a stove.

A) more
B) less
C) the same

Question 5

You blow on food to cool it. Blowing increases

A) conduction.
B) convection.
C) radiation.
D) the specific heat.
E) the latent heat.

Question 6

Which of the following relationships are true for all types of heat engines? (There may be more than one correct choice.)

A) e = 1 - $\frac{\mathrm{T}_{\mathrm{C}}}{\mathrm{T}_{\mathrm{H}}}$

B) e = $\frac{\mathrm{W}}{\left|\mathrm{Q}_{\mathrm{H}}\right|}$

C) e = $\frac{\left|Q_{H}\right|-\left|Q_{C}\right|}{\left|Q_{H}\right|}$

D) = $\frac{\mathrm{T}_{\mathrm{C}}}{\mathrm{T}_{\mathrm{H}}}$
$\left|\frac{\mathrm{Q}_{\mathrm{C}}}{\mathrm{Q}_{\mathrm{H}}}\right|$

E) e = 1 - $\left|\frac{\mathrm{Q}_{\mathrm{C}}}{\mathrm{Q}_{\mathrm{H}}}\right|$

Question 7

A gas is confined to a rigid container that cannot expand as heat energy is added to it. This process is

A) isothermal.
B) isometric.
C) isobaric.
D) isentropic.
E) adiabatic.

Question 8

An ideal gas is compressed to one-half its original volume during an isothermal process. The final pressure of the gas

A) increases to twice its original value.
B) increases to less than twice its original value.
C) increases to more than twice its original value.
D) does not change.

Question 9

As a system loses its ability to do useful work

A) energy increases.
B) entropy decreases.
C) energy decreases.
D) entropy increases.
E) entropy remains constant.

Question 10

A proton is located at x = 1.0 nm, y = 0.0 nm and an electron is located at x = 0.0 nm,
Y = 4.0 nm. Find the attractive Coulombic force between them. (The value of k is
9)0 × 10⁹ N · m²/C².)

A) 1.4 × 10^-11 N
B) 5.3 × 10^-18 N
C) 5.3 × 10⁸ N
D) 5.9 × 10^-15 N

Question 11

Three charges of magnitude 3.0 × 10^-4 C each are located at x = 1.0 m, y = 0.0 m, at x = 0.0 m, y = 0.0 m, and at x = -1.0 m, y = 0.0 m. The one in the middle is negative, while the other two are positive. What is the net Coulombic force exerted by them on a negative 3.0 × 10^-5 C charge located at x = 0.0 m, y = 2.0 m? (The value of k is 9.0 × 10⁹ N · m²/C².)

A) 87 N attractive
B) 87 N repulsive
C) 120 N attractive
D) 120 N repulsive

Question 12

In the figure Q = 5.8 nC and all other quantities are exact. What is the magnitude of the force on the charge Q?

A) 1.8 × 10^-3 N
B) 1.0 × 10^-3 N
C) 9.0 × 10^-4 N
D) 1.2 × 10^-3 N

Question 13

The charge in the bottom right corner of the figure is Q = -45 nC. What is the magnitude of the force on Q?

A) 1.9 × 10^-2 N
B) 1.4 × 10^-2 N
C) 2.6 × 10^-2 N
D) 3.5 × 10^-2 N

Question 14

The charge at the bottom of the figure is Q = + 17 nC. What is the magnitude of the force on the charge Q?

A) 1.9 × 10^-4 N
B) 1.2 × 10^-4 N
C) 1.6 × 10^-4 N
D) 2.3 × 10^-4 N

Question 15

What is the strength of an electric field that a 0.010 C negative charge experiences 0.90 mm from a 0.20 C positive charge? (The value of K is 9.0 × 10⁹ N · m²/C².)

A) 2.2 × 10¹⁵ N/C
B) 5.6 × 10¹⁶ N/C
C) 1.1 × 10¹⁵ N/C
D) 2.2 × 10¹⁶ N/C

Question 16

A point charge Q = -400 nC and two unknown point charges, ^q₁ and ^q₂, are placed as shown. The electric field at the origin O, due to charges Q, ^q₁ and ^q_2, is equal to zero. In the figure, the number of excess electrons in charge Q, is closest to:

A) 2.5 × 10²
B) 1.4 × 10²
C) 2.9 × 10²
D) -1.4 × 10²
E) -2.5 × 10²

Question 17

Two point charges, Q₁ = -1.0 ?C and Q₂ = + 3.0 ?C, are placed as shown. In the figure, the number of excess electrons in charge Q₁ is closest to:

A) 6.3 × 10¹²
B) 6.3 × 10¹³
C) 2.0 × 10¹¹
D) 2.0 × 10¹²
E) 2.0 × 10¹³

Question 18

-A pair of charged conducting plates produces a uniform field of 12,000 N/C, directed to the right, between the plates. The separation of the plates is 40 mm. In the figure, an electron is projected from plate A, directly toward plate B, with an initial velocity of v_o = 2.0 × 10⁷ m/s. The velocity of the electron as it strikes plate B is closest to:

A) 1.2 × 10⁷ m/s
B) 1.5 × 10⁷ m/s
C) 1.8 × 10⁷ m/s
D) 2.1 × 10⁷ m/s
E) 2.4 × 10⁷ m/s

Question 19

A hydrogen nucleus, which has a charge e, is situated to the left of a carbon nucleus, which has a charge 6e. Which statement is true?

A) The electrical force experienced by the hydrogen nucleus is to the left, and the magnitude is equal to the force exerted on the carbon nucleus.
B) The electrical force experienced by the hydrogen nucleus is to the left, and the magnitude is greater than the force exerted on the carbon nucleus.
C) The electrical force experienced by the hydrogen nucleus is to the left, and the magnitude is less than the force exerted on the carbon nucleus.
D) The electrical force experienced by the hydrogen nucleus is to the right, and the magnitude is equal to the force exerted on the carbon nucleus.

Question 20

If you rub a balloon on your sweater and then press it to a wall, it will often stick there. Why does this happen?

A) Rubbing removes a surface layer of grease, allowing the rubber to come in sufficiently close contact with the wall so that air pressure holds it there.
B) Rubbing the balloon charges it electrostatically, and this charge on the balloon induces an opposite charge on the wall. The attraction between the induced charge and the charge on the balloon holds the balloon to the wall.
C) A wall typically has a net electric charge on it, and rubbing the balloon charges it electrostatically. If the wall happens to have opposite charge to that on the balloon, the balloon will stick.
D) Rubbing the balloon causes moisture to condense on it, and surface tension causes the balloon to stick to the wall.
E) Rubbing the balloon surface causes it to become slightly conducting. When the balloon is touched to the wall, electrons flow from the balloon to the wall. This sets up an electric field that bonds the balloon weakly to the wall.