The wattmeter is an electrodynamic instrument for measuring the electric power or the supply rate of electrical energy of any given circuit. The device consists of a pair of fixed coils, known as current coils, and a movable coil known as the potential coil. Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... Electric power is the amount of work done by an electric current in a unit time. ... Electrical energy or electromagnetic energy is a form of energy present in any electric field or magnetic field, or in any volume containing electromagnetic radiation. ... An electrical network or electrical circuit is an interconnection of electrical elements such as resistors, inductors, capacitors, diodes, switches and transistors. ... A coil is a series of loops. ...

The current coils are connected in series with the circuit, while the potential coil is connected across the line. Also, on analog wattmeters, the potential coil carries a needle that moves over a scale to indicate the measurement. A current flowing through the current coil generates an electromagnetic field around the coil. The strength of this field is proportional to the line current and in phase with it. The potential coil has, as a general rule, a high-value resistor connected in series with it to reduce the current that flows through it. Left: Series / Right: Parallel Arrows indicate direction of current flow. ... An analog or analogue signal is any variable signal continuous in both time and amplitude. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Resistor symbols A pack of resistors A resistor is a two-terminal electrical or electronic component that resists the flow of current, producing a voltage drop between its terminals in accordance with Ohms law. ...

The two circuits of a wattmeter are likely to be damaged by excessive current. Both the ammeter and voltmeter are vulnerable to overheating - in case of an overload, the devices' pointers indicate beyond the upper limit of their scales - but in the wattemeter in particular, both the current and potential circuits may be overheating and yet the pointer may not point farther than halfway up the scale. This is because the position of the pointer depends on the power factor, voltage and current. Thus, a circuit with a low power factor will give a low reading on the wattmeter, even when both of its circuits are loaded to the maximum safety limit. Therefore, a wattmeter is rated not in watts, but in volts and amperes. Wire carrying current to be measured Spring providing restoring force An ammeter is a measuring instrument used to measure the flow of electric current in a circuit. ... Two digital voltmeters A voltmeter is a measuring instrument for measuring the voltage between two points in an electric circuit. ... The volt (symbol: V) is the SI derived unit of electric potential difference. ... The ampere (symbol: A) is the SI base unit of electrical current equal to one coulomb per second. ...