# Homework Help: Temperature question

1. Jan 11, 2005

### Danko

Hi I'm having some problems with a question i have to present in class.

If you want to raise the temperature at home, will this work?:
You put a bucket of water in the freezer, remove it when it has frozen and let it melt outside.

Will the house get warmer, and is it possible that more warmth has been created than the electrical energy that has been used.

Can anyone help?

2. Jan 11, 2005

### dextercioby

Yes,the room will definitely warm,but not too much...Air is very bad heat conductor and the quantity of heat will be very small.

For the second part,no...

Daniel.

3. Jan 11, 2005

### HallsofIvy

What are the assumptions here? If you turn on the freezer just to freeze the water, then yes, the freezer will exhaust more heat than is required to melt the ice afterwards. The freezer, like any machine, is not perfectly efficient: it uses slightly more energy than is required. The heat taken out of the water is exhausted into the room along with the additional heat from friction, etc. When you take the ice out of the freezer and let it melt, some of that heat will go into the water but no more than came from the freezing. The heat from the inefficiency of the freezer will remain.

However, you can NOT get more energy out that is put in: you cannot get more warmth than corresponds to the electrical energy. (The heat that was initially in the water and was exhausted from the freezer is back in the water after it melts.)

4. Jan 11, 2005

### Danko

thanks

Thanks for the help!
I think the idea was (although I'm not sure) that the ice was to melt outside the house, in that case shouldn't the warmth that the freezer emits remain in the house thus resulting in a slightly higher temperature?

Secondly about the electrical power....Does the freezer consume any more power than what is needed to power the condenser? Anything proportional to the amount of water?

Also i think you are to assume that the freezer is on already.

5. Jan 11, 2005

### Andrew Mason

I find myself disagreeing with the other two posters on this second point.

I agree that the house will heat up by freezing the ice. But it will warm up by more than the electrical energy used.

The amount that it will warm up will be the heat extracted from the ice plus the work done by the refrigerator (which ultimately is dissipated as heat). So the total heat will necessarily be greater than the amount of work done (ie. power consumed) by the refrigerator (ie. by the amount of heat extracted).

AM

PS. Taking it outside would not necessarily cause it to melt. Not where I am today (-28 deg. C) :grumpy:

Last edited: Jan 11, 2005