Chapter 30, Problem 33A

From water to glass, the change in the speed of light is less than from air to glass. Does this mean a magnifying glass submerged in water will magnify more or less than in air?

To determine

To state whether the total energy of the system remains constant, increases or decreases if work done on it is greater than the heat.

Explanation of Solution

Introduction:

Work is said to be done on a system or by a system if there is a force exerted and there is some displacement in the direction of application of force. It is positive if the system is doing work on the surroundings and it is negative if work is done on the system.

As a body slides or moves over any surface, there is some heat generated on its base on account of the friction acting over there. As a result, both the surface and the part of body in contact with the surface develops heat. Now if we do an external work upon the system, which is equal to the amount of heat generated from it, both the work done and the heat equate each other.

We know that the total energy of a system is a sum total of its kinetic energy and potential energy possessed at that instant, when the couch slides its kinetic energy increases and work is done on it which decreases its overall potential energy, thus keeping the total energy of the system constant. But here in this case, as the work done on the system is greater than the heat produced by it, the total energy of the body should increase.

Conclusion:

If work is greater than the heat produced, the total energy of the system should increase.