Answer: Energy - Energy is referred to as the ability to do work. Energy is measured in units called joules. One kilojoule is equal to a thousand joules.Energy can neither be created nor consumed or destroyed.

Power - Power is the rate of doing work or the rate of using energy, which are numerically the same. If you do 100 joules of work in one second  the power is 100 watts. Power is measured in Watts(W).

Single phase energy meter 

Single phase induction type energy meter is popularly known as watt-hour meter.Induction type energy meter basically includes following components:

• Driving system
• Moving system
• Braking system
• Registering system

Driving System-? Driving system consists of a series magnet and a shunt magnet. The coil of the series magnet is excited by load current while that of the shunt magnet is excited by current proportional to the supply voltage. These two coils are respectively referred as current coil and potential coil of the energy meter.

Moving system - ? Moving system consists of a freely suspended, light aluminum disc mounted on an alloy shaft and placed admidst the air-gap of the two electromagnets.

Braking System-Braking system consists of a position-adjustable permanent magnet placed near one edge of the disc. When the disc rotates in the gap between the two

poles of the brake magnet, eddy currents are set up in the disc. These currents react with the brake magnet field and provide the required braking torque damping out the disc motion if any, beyond the required speed. The braking torque can be adjusted as required by varying the position of the braking magnet.

Registering system-  The registering or counting system essentially consists of gear train, driven either by worm or pinion gear on the disc shaft, which turns pointers that indicate on dials the number of times the disc has turned.

Working of single phase energy meter - In all induction meters we have two fluxes which are produced by two different alternating currents on a metallic disc. Due to alternating fluxes there is an induced emf, the emf produced at one point  interacts with the alternating current of the other side resulting in the production of torque. Similarly, the emf produced at the point two interacts with the alternating current at point one, resulting in the production of torque again but in opposite direction. Hence due to these two torques which are in different directions, the metallic disc moves. This is basic principle of working of an induction type meters.

 Here we have assumed that the pressure coil is highly inductive in nature and consists of very large number of turns. The current flowin in the pressure coil is Ip which lags behind voltage by an angle of 90 degrees. This current produces flux F. F is divided into two parts Fg and Fp. (1) Fg which moves on the small reluctance part across the side gaps. (2) Fp: It is responsible for the production of driving torque in the aluminium disc. It moves from high reluctance path and is in phase with the current in the pressure coil. Fp is alternating in nature and thus emf Ep and current Ip. The load current which is shown in the above diagram is flowing through the current coil produces flux in the aluminium disc, and due this alternating flux there on the metallic disc, an eddy current is produced which interacts with the flux Fp which results in production of torque. As we have two poles, thus two torques are produced which are opposite to each other.