Meaning of symbols in given equation

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SUMMARY

The equation W=JQ from the 1st Law of Thermodynamics defines work (W) as the product of the mechanical equivalent of heat (J) and the heat supplied (Q). In this context, J represents a conversion constant valued at 4.18 joules per calorie, facilitating the conversion between different energy units. The discussion clarifies that both work and heat should be measured in joules for consistency, emphasizing the importance of using SI units in thermodynamic equations.

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  • Understanding of the 1st Law of Thermodynamics
  • Familiarity with energy units: joules and calories
  • Basic knowledge of unit conversion in physics
  • Concept of mechanical equivalent of heat
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  • Explore the implications of using SI units in thermodynamics
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HUMERA.S
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In my textbook, under the subtopic 1st law of of Thermodynamics, an equation is given as foll :
W=JQ
where W=work done ;Q=heat supplied
but they have not mentioned what is J.

please could someone tell me what exactly 'J' stands for in this equation
 
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Is this an old textbook?

J is the symbol for a quantity called 'The mechanical equivalent of heat'.

Both heat and work are forms of energy (as are all the other terms in the First Law) but we need to ensure that they are all in the same units.

At one time, the metric measure for heat was the calorie, whilst the unit for work was the joule. Today we measure it all in joules.

J is simply the conversion constant and is equal to 4.18 joules per calorie.
 
Studiot said:
At one time, the metric measure for heat was the calorie, whilst the unit for work was the joule. Today we measure it all in joules.

And if it was an old American textbook, it might be using Brithsh Thermal Units and horsepower...

It's mich simpler to use SI units, and measure both heat and work in the same units (joules).
 
well yeah I know in S.I. 'J' stands for joule...

but in the equation W=JQ ; if we consider W(work) and Q(energy) in the same units, then here J seems to be some constant with no units and no dimensions ! [as 'J' relates W & Q with a multiplication and not addition or substaction]

the equation was not given while solving a problem , but was stated like it is a basic formula.
 
HUMERA.S said:
but in the equation W=JQ ; if we consider W(work) and Q(energy) in the same units, then here J seems to be some constant with no units and no dimensions ! [as 'J' relates W & Q with a multiplication and not addition or substaction]

the equation was not given while solving a problem , but was stated like it is a basic formula.
By looking through other worked problems in that textbook you should be able to deduce the system of units that book uses.

I believe Studiot provided you with a very good explanation:

Work (in joules) = (4.18 joules per calorie) x Q (in calories)

illustrating how J has a value and units
 
"Work (in joules) = (4.18 joules per calorie) x Q (in calories)"

Wow really its clear now !
Thanks a lot
 

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