Unit 13

what do you know about the internal energy of an object that behaves as a net radiator?

Not much because internal energy is not temperature

After a sunny day, which will be warmer. A black or white road surface?

The black surface

why does the sun have shorter wavelengths of radiant energy than earth?

The sun has a higher temperature than the earth !

Do we currently have the technology for solar power stations in orbit?

This technology already exists

Does Newton's law of cooling apply to heating?

To both of cooling and heating

On a hot summer day you need to leave your cool air conditioned house for 30 minutes. To save energy, what should you do to the thermostat?

Turn it off

in what color metal pot will cold water warm to room temperature faster?

a black pot

in what color metal pot will hot water cool faster?

a black pot

if a material is a good conductor of heat, how good of an insulator might it be?

a poor insulator !

we feel uncomfortably warm on a muggy day because water molecules are preventing the evaporation from our moist bodies.

preventing the evaporation from our moist bodies

as the temperature of a piece of metal increases, what happens to the wavelength of its radiation?

radiation wavelengths get shorter

when a gas disc hanged to a liquid phase the gas

releases energy

evaporation is a cooling process and condensation is a

warming process

under what conditions will an object be a net radiator of energy?

when its temp is higher than its surroundings

how does a material absorb heat?

"all of these" - conduction - convection - radiation

the reason the sun's radiant energy is of shorter wavelengths than the earths is because the sun - has a higher temperature - is an energy source - has more thermal energy - all of these

- all of these: - has a higher temperature - is an energy source - has more thermal energy

Wood conducts heat very poorly - it has a very low conductivity. Does wood still have a low conductivity if it is hot? Select one: a. Yes b. No

a. Yes Explanation: Because wood is a good insulator (poor conductor of heat). not sure if correct yet

The planet Earth loses heat mainly by Select one: a. radiation. b. convection. c. conduction.

a. radiation. Explanation: This is because there is no material medium beyond the atmosphere. There is a complete vacuum. So, heat loss from the earth means heat is going away into space, leaving the earth with no medium requirement. Hence, the mode of heat loss must be radiation. Conduction and convection require a material medium to transfer heat from one point to another. Radiation does not require any medium. Radiation can pass through a vacuum also. not sure if correct yet

When should you add cream to your hot coffee so that the coffee is the hottest when you are ready to drink within a few minutes after being served? - add the cream right when the coffee is served - add the cream just before you drink it - it won't really matter when you add the cream

add the cream right when the coffee is served

Both black and white road surfaces absorb sunlight. At the end of a clear night, the warmer road surface will be Select one: a. The black surface. b. The white surface. c. There is no difference.

b. The white surface. not sure if correct yet

An object will normally be a net radiator of energy when its temperature is Select one: a. lower than its surroundings. b. higher than its surroundings.

b. higher than its surroundings. not sure if correct yet

Your feet feel warmer on a rug than on a tile floor because the rug Select one: a. all of these. b. is a better insulator than tile. c. is usually warmer than tile. d. has more internal energy than tile.

b. is a better insulator than tile. not sure if correct yet

steam burns more damaging than burns cause by boiling water because steam

both of these: - gives up additional energy when it condenses - has more energy than boiling water

which glows with. electromagnetic waves: the sin or the earth

both the sun and the earth Earth glows in long-wavelength radiation, while the Sun glows in shorter waves.

Many tongues have been injured by licking a piece of metal on a very cold day. The heat is transferred from their tongue allowing it to freeze to the pole by a process of Select one: a. convection. b. radiation. c. conduction.

c. conduction. Explanation: Conduction is the transfer of Thermal Energy by touching. not sure if correct yet

what phase of matter holds convection as a significant mechanism for heat transfer?

fluids !

If an object absorbs radiation well, then it is also a

good emitter of radiation

evaporation is a cooling process because

heat is radiated during the process

If you were caught in freezing weather with only a candle for heat, you would be warmer in a .. igloo tent, wooden house, car

igloo Explanation: Snow has low density makes it an insulator so can keep warm very well. Igloo is built by Snow. Igloo has snow cover outside it which is bad conductor of heat. With the candle you can keep the inside warmer. Wooden house would be the next best thing bc wood is also bad conductor of heat. The car isn't a good option because its made of metal which is a bad insulator but a good conductor of heat. The tent I don't really know how to explain that one other than its a bad insulator. I don't know if its a good conductor.

what happens to the internal energy of an object as it radiates more energy than it absorbs?

internal energy decreases

Given the same temperature, which moves faster. Light gaseous molecules or heavy gaseous molecules?

light gaseous molecules move faster

when heat is added to boiling water, the water temperature

stays the same

why won't a paper cup filled with water burn if held to a flame?

the paper cannot become much hotter than the water it contains Explanation: In the demonstration video from the last module (mod. 12) there is a video of two water balloons above a flame. One filled with water, and one with air. The balloon with air pops immediately over the flame, while the water balloon takes a very long time. This is the same concept with the water cup. Water has a high specific heat and takes a long time to change temperature. The thermal energy from the flame gets absorbed by the water faster than the cup can in this case and causes the cup to not burn.

why does a rug feel warmer than a stone floor at the same temperature?

the rug is a better insulator than stone

what happens to the average speed of helium atoms when you double their absolute temperature (assume a non-deal gas)

the temperature less than doubles Explanation: Because the molecules are not colliding, so there is nothing to produce heat. Heat is produced through conduction when energy is being transferred between molecules when they collide. If no collision is happening, there is no conduction and no heat production, resulting in no temperature change.

What would happen to the temperature of an object being a poor absorber but a good emitter?

the temperature would become less than its surroundings !

what is the molecules of a gas never collided with each other. What would happen to the temperature of the gas?

the temperature would stay the same

After a clear sky night, which will be warmer. A black or white road surface?

the white surface !

How do the radiation waves emitted by Earth compare to the waves emitted by the Sun?

they're the same except for their frequencies and wavelengths

Why are the glass walls of a thermos bottle coated with silver?

to minimize radiation.

we are warmed by condensation because water molecules in the air that strike our bodies

transfer some of their kinetic energies to us.