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Heat

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October 24, 2009 3:15:32 PM

If my computer uses 100 watts, a light bulb uses 100 watts and an electric heater uses 100 watts, which will give off the most heat?

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a b D Laptop
October 25, 2009 12:18:49 AM

Your question is too simple to answer - there are many more things to consider. Heat itself (the transfer of thermal energy) is best characterized as a differential equation - as such, heat is a function of time. At any infinitesimally small amount of time, any one of them can transfer more heat than the other two; however, that may not be the case as time goes on.
You also need to consider area; heat/unit area, specifically. Your computer's processor can give off tons of heat over time, but most of it is concentrated on a very small area - the processor die. However, an electric heater is designed to give off some heat over a very large area, that area being a room.
You also have to consider that the computer processor and heater, unlike the light bulb, do not generate constant heat per unit time. Both of them may be throttled up or down, depending on what you do with them.
Also, the computer uses technology to dissipate heat very quickly, as opposed to the light bulb, which does not.

http://en.wikipedia.org/wiki/Heat

October 26, 2009 5:32:24 PM

frozenlead said:
Your question is too simple to answer - there are many more things to consider. Heat itself (the transfer of thermal energy) is best characterized as a differential equation - as such, heat is a function of time. At any infinitesimally small amount of time, any one of them can transfer more heat than the other two; however, that may not be the case as time goes on.
You also need to consider area; heat/unit area, specifically. Your computer's processor can give off tons of heat over time, but most of it is concentrated on a very small area - the processor die. However, an electric heater is designed to give off some heat over a very large area, that area being a room.
You also have to consider that the computer processor and heater, unlike the light bulb, do not generate constant heat per unit time. Both of them may be throttled up or down, depending on what you do with them.
Also, the computer uses technology to dissipate heat very quickly, as opposed to the light bulb, which does not.

http://en.wikipedia.org/wiki/Heat

Dear frozenlead, The reason for asking my original question is that I believe that although light bulbs create both light and heat, the light is quickly absorbed and changed to heat, consequently all the electricity is converted to heat. I believe that any appliance whether it be a TV, microwave oven, light bulb, blender or a water heater will convert electrical energy to heat at 100% efficiency. I believe a GE energy smart bulb uses 23% of the electricity that a 100 watt incandescent uses, and creates only 23% of the heat. Any heat created by electricity within a home during the heating season will heat the home. Marilyn Vos Savant and others seem to think that heat created by a dimmer switch is wasted heat but I say it is not, it is helping to heat the home.
a b D Laptop
October 26, 2009 7:12:45 PM

Nothing converts energy to 100% heat, but I do understand what you're trying to say. Your definition of the word "efficiency" is different than that of most people's.

For example, take a lightbulb with a dimmer switch. Let's also consider the bulb will create 60% heat and 40% light. All of the energy that is put into the circuit will come out of it - it's 100% efficient in that frame of reference, but that's a law of physics: energy cannot be created nor destroyed. In that case, you are correct - all of the energy is used. However, when people generally use the term efficiency, they mean the ratio between what you put in and how much you get out of what you want to get out. The point of a lightbulb is to make light, not heat. In that case, our example light bulb is indeed 40% efficient, because we put in 100% electrical energy, and we only got 40% back of what we wanted, light. Since the lightbulb is connected to the dimmer, the dimmer also has an efficiency, converting some of our 100% electricity to heat and electricity (but a lesser amount). Thus, our bulb outputs less of what we wanted since it gets less power (which is scientifically less efficient, but the trade off in real life is that you can vary the light level!).

In other words, since the heat is not what's desired from the bulb, it is considered inefficient. While heating the home may be a good thing in some cases, it's not in all (heat is a very bad thing to have in your home in the desert, or in Florida). However, anyone who buys a light bulb wants light from it: thus, the light is desired.

Edit: Consider a car. If I put gasoline in the engine and start it, wait until all the gas is gone, and get out, not having gone anywhere, is that 100% efficient?
!