Physics 2 exam 4

When you put an ice cube in a glass of warm tea, which of the following happens? a) Heat flows from the tea into the ice cube. b) Cold flows from the ice cube into the tea and heat flows from the tea into the ice cube. c) Cold flows from the ice cube into the tea. d) Neither heat nor cold flows. Only temperature flows between the ice and the tea.

a) Heat flows from the tea into the ice cube. A common misconception is that "cold" flows from the ice into the tea. When the ice is placed in the tea, the ice has less kinetic energy per molecule than the tea and so in molecular collisions between the tea and ice, energy transfers from the tea into the ice. This energy transfer cools the tea as it melts the ice and then heats up the ice. The transfer of energy from the warmer tea to the colder ice is called "heat."

A gas is compressed to one-half of 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

a) Increases to twice its original value

Which of the following statements are true? Check all that apply. a) Liquid water expands with increasing temperature between 0°C and 4°C. b) Solid ice is less dense than liquid water. c) Water contracts as it freezes at 0°C. d) Liquid water expands with increasing temperature above 4°C.

a) Liquid water expands with increasing temperature above 4°C. b) Solid ice is less dense than liquid water.

Ten grams of water is added to ten grams of ice in an insulated container. Will all of the ice melt? a) More information is needed. b) No. c) Yes.

a) More information is needed. The problem does not specify the initial temperatures of the ice and water. If the ice and water are both initially at 0∘C, then none of the ice will melt, since heat will not transfer between them. Alternatively, if the ice is at 0∘C and the water is at 100∘C, then the water can provide Q=mcΔT=(0.010kg)(4186J/kg⋅ ∘C)(100∘C)=4186J of heat as it cools to 0∘C. The ice only needs Q=mL=(0.010kg)(333kJ/kg)=3330J to completely melt, and so in this case all the ice would melt. Since the water could provide more heat than needed, you need to know the initial temperatures of the ice and water to determine just how much of the ice would melt.

Two equal-mass liquids, initially at the same temperature, are heated for the same time over the same stove. You measure the temperatures and find that one liquid has a higher temperature than the other. Which liquid has the higher specific heat? a) The cooler one. b) The hotter one. c) Both are the same.

a) The cooler one. The two objects absorb the same amount of heat from the stove. From Q=mcΔT, given that the masses are the same, the object with the higher specific heat will experience the smaller temperature increase and will therefore be cooler.

Radiation is emitted a) by any object not at 0 K. b) only by objects with more caloric than their -surroundings. c) only by objects that have a large specific heat. d) only by glowing objects such as the Sun. e) only by objects whose temperature is greater than the temperature of the surroundings.

a) by any object not at 0 K. Radiation is emitted by all objects not at absolute zero. Very hot objects, such as the Sun, emit radiation in the visible spectrum so they appear to be glowing. If the temperature of an object is less than its surroundings, it has a net gain in energy as it absorbs more radiation than it emits. However, it is still emitting radiation. The amount of radiation emitted is independent of the object's specific heat.

An ideal gas is compressed isothermally to one-third of its initial volume. The resulting pressure will be a) three times as large as the initial volume b) less than three times as large as the initial volume c) more than three time as large as the initial volume d) equal to the initial value e) impossible to predict based on this data

a) three times as large as the initial volume

When the first law of thermodynamics ΔU= Q-W is applied to an ideal gas that is taken through an isothermal process, a) ΔU=0 b) W=0 c) Q=0 d) none of the above

a) ΔU=0

An ideal gas undergoes an adiabatic expansion, a process in which no heat flows into or out of the gas. As a result, a) The temperature of the gas remains constant and the pressure decreases b) Both temperature and pressure of the gas decrease c) The temperature of the gas decreases and the pressure increases d) Both the temperature and volume of the gas increase e) Both temperature and pressure of the gas increase

b) Both temperature and pressure of the gas decrease

Which of the following happens when a material undergoes a phase change? a) The temperature changes. b) Heat flows into or out of the material. c) The molecules break apart into atoms. d) The chemical composition changes.

b) Heat flows into or out of the material. Phase changes occur at specific temperatures (melting point, boiling point, or sublimation point) while heat is being added or removed from the material. During the phase change the temperature remains constant. The thermal energy at this temperature is equal to the intermolecular binding energy. These energies are much lower than the energy necessary to break the molecules apart into their atoms, or to change the chemical composition of the molecules.

In an isothermal process, there is no change in a) Pressure b) Temperature c) Volume d) Heat

b) Temperature

In a mixture of the gases oxygen and helium, which statement is valid? a) Both will be moving at the same speed. b) The helium atoms will be moving faster than the oxygen molecules, on average. c) The kinetic energy of helium atoms will exceed that of oxygen molecules. d) The oxygen molecules will, on average, be moving more rapidly than the helium atoms. e) None of the above.

b) The helium atoms will be moving faster than the oxygen molecules, on average. In the mixture, the oxygen molecules and helium atoms will be at the same temperature, which means that their average molecular kinetic energies will be the same. Since a helium atom has less mass than an oxygen molecule, the helium atoms will be moving faster than the oxygen molecules on average.

A steel plate has a hole in it with a diameter of exactly 1.0 cm when the plate is at a temperature of 20 ∘C. A steel ring has an inner diameter of exactly 1.0 cm at 20 ∘C. Both the plate and the ring are heated to 100 ∘C. Which statement is true? a) The opening in the ring gets larger, but we need the relative size of the plate and the hole to know what happens to the hole. b) The hole in the plate and the opening in the ring get larger. c) The hole in the plate gets larger, and the opening in the ring gets smaller. d) The hole in the plate and the opening in the ring get smaller. e) The hole in the plate gets smaller, and the opening in the ring gets larger.

b) The hole in the plate and the opening in the ring get larger. Many students have the misconception that as the plate expands, the hole will get smaller. To understand what actually happens, imagine that the hole is filled with a steel disk. As the plate and the steel disk are heated both will expand. After the plate and disk are heated, the disk is removed from the plate. Since the disk expanded, the hole that is left must also have expanded. As the steel ring is heated its circumference will expand causing its interior to also expand.

Which of the following does the internal energy of an ideal gas depend upon? a) The internal energy depends upon its volume. b) The internal energy depends upon its temperature. c) The internal energy depends upon its pressure.

b) The internal energy depends upon its temperature.

As heat is added to water, is it possible for the temperature measured by a thermometer in the water to remain constant? a) No, adding heat will always change the temperature. b) Yes, the water could be changing phase. c) Maybe; it depends on the rate at which the heat is added. d) Maybe; it depends on the initial water temperature.

b) Yes, the water could be changing phase. A common misconception is that as heat is added to water the temperature will always rise. However, the heat is added to water at its melting and boiling points without the temperature changing. At these temperatures the water is undergoing a phase change.

By which primary heat transfer mechanism does the Sun warm Earth? a) convection b) radiation c) conduction

b) radiation

In a given reversible process, the temperature of an ideal gas is kept constant as the gas is compressed to a smaller volume. Which one of the following statements about the gas is correct a) the gas must absorb heat from its surroundings b) the gas must release heat to its surroundings c) the pressure of the gas always remains constant d) the process is adiabatic e) impossible to predict based on this data

b) the gas must release heat to its surroundings

For objects at thermal equilibrium, which of the following is true? a) Each has the same heat. b) Each has the same internal energy. c) Each is at the same temperature. d) All of the above. e) None of the above.

c) Each is at the same temperature. When two objects are in thermal equilibrium heat does not transfer between them. This occurs when the two objects are at the same temperature. Internal energy is an extrinsic property that depends upon the amount of the substance present. Therefore, two gases in thermal equilibrium with each other would have different internal energies if one consisted of one mole of gas and the other consisted of two moles of gas. Heat is a transfer of energy between objects that are not in thermal equilibrium. Heat is not a property of an object.

Both beakers A and B in the figure contain a mixture of ice and water at equilibrium. Which beaker is the coldest, or are they equal in temperature? a) Beaker A. b) Beaker B. c) Equal.

c) Equal. Students frequently interpret having more ice with being colder. However, whenever ice and water are mixed together and are in thermal equilibrium they will be at the melting/freezing point of the water. Therefore the two containers will be at the same temperature.

Which temperature scale does NOT have negative values? a) Fahrenheit temperature scale b) Celsius temperature scale c) Kelvin temperature scale d) All of the temperature scales have negative values. e) None of the temperature scales has negative values.

c) Kelvin temperature scale

Rod A has twice the diameter of rod B, but both are made of iron and have the same initial length. Both rods are now subjected to the same change in temperature (but remain solid). How would the change in the rods' lengths compare? a) Rod A > rod B. b) Rod B > rod A. c) Rod A = rod B. d) Need to know whether the rods were cooled or heated.

c) Rod A = rod B. Students may confuse thermal expansion with elasticity and surmise that the narrower rod would expand more for the same temperature change. However, in thermal expansion the change in length is independent of the rods diameter or cross-sectional area.

Two objects are made of the same material, but they have different masses and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change? a) The one with the higher initial temperature. b) The one with the greater mass. c) The one with the lesser mass. d) The one with the lower initial temperature. e) The one with the higher specific heat. f) Not enough information.

c) The one with the lesser mass. As the two objects are in thermal contact, the heat given off by the hot object will equal the heat absorbed by the cold object. The objects have the same specific heat so the heat transfer is proportional to the product of the mass of each object and its change in temperature. The object with the smaller mass will then have the larger temperature change.

The temperature of an ideal gas increases. Which of the following is true? a) The volume must increase while the pressure decreases. b) The pressure must increase while the volume decreases. c) The pressure, the volume, or both, may increase. d) The pressure must increase. e) The pressure must decrease.

c) The pressure, the volume, or both, may increase. A common misconception is that if the temperature increases both the pressure and volume will increase. However, by the ideal gas law, when the temperature increases the product of the pressure and volume must increase. This increase can occur by increasing the pressure, increasing the volume, or both.

When the first law of thermodynamics ΔU= Q-W is applied to an ideal gas that is taken through an adiabatic process, a) ΔU=0 b) Q=0 c) W=0 d) none of the above

c) W=0

By which primary heat transfer mechanism does one end of a steel rod become hot when the other end is placed in a flame? a) radiation b) convection c) conduction

c) conduction

By which primary heat transfer mechanism does a stove heat a pot of soup? a) conduction b) radiation c) convection

c) convection

Heat is a) measure of the average kinetic energy of atoms. b) the total kinetic energy of an ideal gas. c) the amount of energy transferred between objects as a result of a difference in temperature. d) invisible, odorless, weightless substance. e) fluid called caloric.

c) the amount of energy transferred between objects as a result of a difference in temperature. Students often think that heat is a substance or a property of a material. When two materials are at different temperatures (that is, they have different average kinetic energies per molecule), energy can transfer from the hot object to the cold object. This transfer of energy is called heat.

An ideal gas is in a sealed rigid container. The average kinetic energy of the gas molecules depends most on a) the number of molecules in the container. b) the size of the container. c) the temperature of the gas. d) the mass of the molecules.

c) the temperature of the gas. The temperature of the gas is a measure of the average kinetic energy of the gas molecules.

An ideal gas undergoes an isothermal process. Which of the following statements are true? (i) No heat is added to or removed from the gas. (ii) The internal energy of the gas does not change. (iii) The average kinetic energy of the molecules does not change a) (i) only b) (i) and (ii) only c) (i) and (iii) only d) (ii) and (iii) only e) (i), (ii), and (iii). f) None of the above

d) (ii) and (iii) only

The linear expansion of a material depends on which of the following? a) The change in temperature of the material. b) The length of the material. c) The type of material. d) All of the above. e) Both the change in temperature and the type of the material.

d) All of the above. Equation for thermal expansion shows that the change in length depends upon the initial length, the change in temperature, and the coefficient of thermal expansion (which depends upon the type of material).

An ideal gas undergoes an isothermal expansion from state A to state B. In the process (use sign conventions) a) Q=0, ΔU=0, W>0 b) Q>0, ΔU=0, W<0 c) Q=0, ΔU>0, W>0 d) Q>0, ΔU=0, W>0 e) Q=0, ΔU<0, W<0

d) Q>0, ΔU=0, W>0

In an isobaric compression of an ideal gas, a) No heat flows into the gas b) The internal energy of the gas remains constant c) No work is done on the gas d) Work is done on the gas e) Work is done by the gas

d) Work is done on the gas

A gas is quickly compressed in an isolated environment. During the event, the gas exchanged no heat with its surroundings. This process is a) isobaric b) isochoric c) isothermal d) adiabatic

d) adiabatic

A typical thermos bottle has a thin vacuum space between the shiny inner flask (which holds a liquiand the shiny protective outer flask, often stainless steel. The vacuum space is excellent at preventing a) conduction, convection, and radiation. b) radiation. c) convection. d) conduction and convection. e) conduction.

d) conduction and convection. Heat is able to transfer through a vacuum by radiation, but heat requires a medium to transfer by conduction and by convection. Therefore the vacuum in a thermos prevents heat loss by conduction and convection.

An ideal gas is compressed isobarically to one-third of its initial volume. The resulting pressure will be a) three times as large as the initial volume b) less than three times as large as the initial volume c) more than three time as large as the initial volume d) equal to the initial value e) impossible to predict based on this data

d) equal to the initial value