Watts/Heat relationship (dumb question)

[Rene]

Suppose that I have a light bulb consuming 100 watts, a radio also consuming
100 watts and an electric heater also consuming 100 watts.



If I were to measure the heat generated by all these 3 devices, would I get
the same amount of heat? In other words, would all devices consuming the
same wattage (solid state, no moving parts) generate the same amount of
heat?



Thank you.

 

[John Popelish]

Rene wrote:

Suppose that I have a light bulb consuming 100 watts, a radio also consuming
100 watts and an electric heater also consuming 100 watts.

If I were to measure the heat generated by all these 3 devices, would I get
the same amount of heat? In other words, would all devices consuming the
same wattage (solid state, no moving parts) generate the same amount of
heat?

Thank you.

In a very general way, watts are heat, unless you can follow then to
some other end (like potential energy or chemical energy etc.) If you
put each of the devices you mention in calorimeters (devices that
measure heat by how much the temperature of a known thermal mass rises
in a given period of time (and if you compensated for the heat stored
in the devices, themselves) it would not matter what device consumed
the watts or what voltage this power was driven by. Watts convert
directly to calories which are measure of heat energy.

--
John Popelish

 

[peterken]

yes, if they all converted exactly the same amount of energy into something
else (movement, light, sound)
no, if they all convert different amounts of energy into something else

the bulb will convert an amount into light, the non-light-energy will be
turned mostly into heat
the heater will have losses in light-radiation (usually IR), the rest will
be dissipated as heat
the radio will convert energy into sound, the rest will be dissipated as
heat

so it all depends on the efficiency of every aparatus that will be compared


"Rene" <nospam@nospam.nospam> wrote in message
news:UYidd.394645$mD.336927@attbi_s02...

Suppose that I have a light bulb consuming 100 watts, a radio also consuming
100 watts and an electric heater also consuming 100 watts.

If I were to measure the heat generated by all these 3 devices, would I get
the same amount of heat? In other words, would all devices consuming the
same wattage (solid state, no moving parts) generate the same amount of
heat?

Thank you.

 

[Dr Engelbert Buxbaum]

Rene wrote:

The light bulb and the radio will put out a fraction of their energy
as light or sound respectively, so it's not all heat. However, it
doesn't take long before that light and sound will hit something, not
bounce off and be converted into heat.

So, does this mean that at the end, they will all be generating the same
amount of heat?

There is something called the first law of thermodynamics which states
that energy can not be created or destroyed. However, different forms of
energy can be interconverted. Thus you can turn electrical energy into
heat, light or sound.

However, these energies have different "values" because of the second
law of thermodynamics. Crudely speaking, this law states that the amount
of disorder ("entropy") increases in an isolated system during each
reaction. Thus electrical energy, with its ordered flow of electrons,
can be turned into heat (random motion of molecules) with 100%
efficiency. The reverse reaction is possible only with a loss, thus the
efficiency of a power station is limited to 40% or so.

If the universe is considered an isolated system (which can not be
proven), than all forms of energy must eventually be converted to heat
because of the second law of thermodynamics, und this heat must
distribute evenly throughout the universe. Once this has happend, no
further reactions will be possible.

Thus, in this sense, the answer to your question is: Yes.

 

[Rene]

One more thing, assume they also use the same voltage.


"Rene" <nospam@nospam.nospam> wrote in message
news:UYidd.394645$mD.336927@attbi_s02...

Suppose that I have a light bulb consuming 100 watts, a radio also
consuming 100 watts and an electric heater also consuming 100 watts.



If I were to measure the heat generated by all these 3 devices, would I
get the same amount of heat? In other words, would all devices consuming
the same wattage (solid state, no moving parts) generate the same amount
of heat?



Thank you.

 

[Rene]

The light bulb and the radio will put out a fraction of their energy
as light or sound respectively, so it's not all heat. However, it
doesn't take long before that light and sound will hit something, not
bounce off and be converted into heat.

So, does this mean that at the end, they will all be generating the same
amount of heat?

 

[rayjking]

Hi,

The light bulb is resistive and is purchased for the value of the watts.
This assumes the filament is at the correct temperature for visible light
conversion.
Other items ( small motors and radios and other items that convert ac into
dc are given a rating of peak power ( watts ) so as to be easy to calculate
a fuse that should be used in the main switch box to survive repetive re
starts after power outages ).

Ray




"Rene" <nospam@nospam.nospam> wrote in message
news:UYidd.394645$mD.336927@attbi_s02...

Suppose that I have a light bulb consuming 100 watts, a radio also
consuming
100 watts and an electric heater also consuming 100 watts.



If I were to measure the heat generated by all these 3 devices, would I
get
the same amount of heat? In other words, would all devices consuming the
same wattage (solid state, no moving parts) generate the same amount of
heat?



Thank you.

 

[rayjking]

"rayjking" <rayjking@bellsouth.net> wrote in message
news:Izudd.185323$as2.86814@bignews3.bellsouth.net...

Hi,

The light bulb is resistive and is purchased for the value of the watts.
This assumes the filament is at the correct temperature for visible light
conversion.
Other items ( small motors and radios and other items that convert ac
into
dc are given a rating of peak power ( watts ) so as to be easy to
calculate
a fuse that should be used in the main switch box to survive repetive re
starts after power outages ).

Ray


I forgot to add that the last group never uses the average amount of watts
on the lable but uses maybe one half .

Ray

"Rene" <nospam@nospam.nospam> wrote in message
news:UYidd.394645$mD.336927@attbi_s02...
Suppose that I have a light bulb consuming 100 watts, a radio also
consuming
100 watts and an electric heater also consuming 100 watts.



If I were to measure the heat generated by all these 3 devices, would I
get
the same amount of heat? In other words, would all devices consuming the
same wattage (solid state, no moving parts) generate the same amount of
heat?



Thank you.

 

[Lord Garth]

"rayjking" <rayjking@bellsouth.net> wrote in message
news:zSBdd.38196$pi7.10559@bignews4.bellsouth.net...

Peter,
With the rising oil/energy prices I may convert back to head phones in the
less than 5 watt range.

Ray

Let's hope you don't actually need 5 watts when using headphones!