A current of 2A flows in a wire offering a resistance of 10ohm. Calculate the energy dissipated by the wire in 0.5 hours.

Options

A. 72Wh
B. 72kJ
C. 7200J
D. 72kJh

Explanation

Consider series connection of elastic springs held horizontally.
When the free end of this connection is pulled slightly and then released, disturbance is said to be produced in the first spring as its length changes from its normal condition. We find that it expands and contracts periodically. In other words, first spring starts oscillating about its mean position.
Now, because of elasticity property of the medium, such disturbance is found to be moving away from free end continuously, making second spring oscillating, then third spring and so on (depending upon length of medium).
Thus, here disturbance is found to be moving from one end to another end which is nothing but propagation of wave in the elastic medium.
Such waves are mechanical because an elastic medium is required for their propagation. Moreover these waves are said to be longitudinal because particles of medium oscillate parallel to direction of propagation of wave.
Another example : Consider a stationary train whose coaches (compartments or bogies) are coupled successively by elastic springs. During the shunting of a train. i.e. While connecting an engine with the first coach, it starts vibrating which in turn makes second coach vibrating, then third, then fourth and so on. Thus a push or jerk given to first coach is found to be affecting all the coaches turn by turn. Such a motion of disturbance is also called propagation of wave in the medium of a train. This wave is also mechanical and longitudinal.