An electric heater supplies heat to a system at a rate of 100W. If system performs work at a rate of 75 joules per second. At what rate is the internal energy increasing?
Solution and Explanation
Heat is supplied to the system at a rate of 100 W.
∴Heat supplied, Q = 100 J/s
The system performs at a rate of 75 J/s.
∴Work done, W = 75 J/s
From the first law of thermodynamics, we have:
Q = U + W
Where,
U = Internal energy
∴ U = Q – W
= 100 – 75
= 25 J/s
= 25 W
Therefore, the internal energy of the given electric heater increases at a rate of 25 W.
Top Questions on Thermal equilibrium
Two cylinders A and B of equal capacity are connected to each other via a stopcock. A contains a gas at standard temperature and pressure. B is completely evacuated. The entire system is thermally insulated. The stopcock is suddenly opened. Answer the following :
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Concepts Used:
Internal Energy
Internal Energy is the microscopic energy contained within a system formed by the disordered movement of molecules (kinetic energy), Potential energy, and the nuclear energy present within the atoms of these molecules. It should be noted that the kinetic energy of molecules present in the system and not the kinetic energy of the system is calculated in the Internal Energy.
The Internal Energy is denoted by ‘U’ and is measured in Joules (J). This Internal Energy can increase with the increase in temperature and change of state or phase (from solid to liquid to gas). Heat Reservoirs store this Internal Energy.
Different Substances will have different Internal Energies depending on the atom, temperature, bonds, pressure, etc.
Forms of Internal Energy:
There are two forms of Internal Energy namely Kinetic Energy and Potential Energy
- Kinetic Energy: Kinetic Energy is the energy produced by the particles due to their motion. The motion of particles can be Rotational, Translational, Vibrational, etc., and hence the energies from these movements will be Translational Energies, Vibrational Energies, Rotational Energies, etc.
- Potential Energy: Potential Energy can be achieved from different types of interaction between particles, nuclear energy, electronic energy, etc.