State and explain first law of thermodynamics 1 physics
Answers
STATEMENT : the amount of heat supplied to a system is equal to the algebraic sum of
the change in internal energy of the system and the amount of external work done
EXPLANATION: when ∆ Q is the quantity of heat supplied to system ,a system a part of it is used to increase its internal energy ∆U and the rest is used in doing external work ∆ W .
The mathematical expression of this law is
∆Q = ∆U + ∆W .
it is a special case of the law of conservation of energy
EXAMPLE: the explosive of a fire crakers in an insulated steel drum
SIGN CONVENTION :
1) work done ∆W by the system is +ve and work done on the system is -ve
2) heat is supplied (∆Q) to the system is + ve ,heat taken from the system is -ve
3) increase in internal energy (∆U) is + ve and decrease in internal energy is -ve
the limitations of this law are
1) it does not tell about the direction of heat flow
2) it does not tell about the efficiency with which heat can be converted into work
hope it may be helpful for you
According to the first law of thermodynamics, during any transformation, there is conservation of energy.
In the case of closed thermodynamic systems, it is stated as follows:
"During any transformation of a closed system, the variation of its energy is equal to the quantity of energy exchanged with the external environment, by thermal transfer (heat) and mechanical transfer (labor). "
ΔQ = ΔU + W
where,
Q = Heat supplied to system
U = Increase in internal energy
W = Work done by system
The variation of the energy of a system which undergoes a transformation can be expressed according to the following relation:
ΔE = ΔU + ΔEc + ΔEp = W + Q
ΔE = the sum of the different energy variations of the system.
ΔU = increase in internal energy
ΔEc = the variation of the macroscopic kinetic energy of the system
ΔEp = the variation of the potential energy of the system
ΔW = Work done by system
ΔQ = Heat supplied to a system