Question

1. _____ - _____is often referred to as heat.?

2. Total Potential Energy equation is?

3.What is the equation for electric power?

Answer 1

1. (Change in internal energy - Work done) is referred to as Heat.

From the First Law of Thermodynamics, we know that: .

Here Q is the Heat added to the system, and W is the Work done on the system and   is the change in Internal Energy of the system. So, Heat  .

2. According to the law of conservation of energy, Total Energy = Kinetic Energy (KE) + Potential Energy (PE).

In Electrostatics, the Potential Energy of a Point Test Charge 'q' placed in any medium is given by :

, where is the permittivity of the medium. Here, 'Q' is considered to be the source charge due to whose electric field, the test charge q is experiencing a force.

In other words, PE = qV(r) , where V(r) is the electric potential at the point 'r' where 'q' is placed.

Since Potential Energy follows superposition principle, we can express the Total Potential Energy of a system of charges as:

for example: considering a 3 charge system in free space, we have

Total PE =

This can be similarly extended for any number of point charges.

as following:

where is the potential experienced by the charge due to all other charges present , and is given by:

  

Similarly for Gravitational interaction,the potential energy of a test mass under the gravitational influence of another mass M is given by:

where minus sign indicates the attractive nature of potential.

Here also, in the case of a system of masses, the superposition principle can be applied as we have done in the case of electric charges above.

3. Electric Power is given by , where V is the electric potential and I is the current.

From Ohm's law , we have

Therefore ,when we have constant current in the circuit.

Also, , at constant voltage. This can be obtained by substituing I = V/R.