# Electromagnetic Induction

## Applications

An electrical generator is an apparatus that converts mechanical energy into electrical energy. In this case the magnetic field is stationary and does not vary with time. It is the circuit that is made to rotate through the magnetic field. Since the area that admits the passage of magnetic field lines changes while the circuit rotates, the flux through the circuit will change, thus inducing a current (Figure 4). Generally, a turbine is used to provide the circuit's rotation. The energy required to move the turbine may come from steam generated by nuclear or fossil fuels, or from the flow of water through a dam. As a result, the mechanical energy of rotation is changed into electric current.

Transformers are devices used to transfer electric energy between circuits. They are used in power lines to convert high voltage electricity into household current. Common consumer electronics such as radios and televisions also use transformers. By making use of mutual inductance, the transformer's primary circuit induces current in its secondary circuit. By varying the physical characteristics of each circuit, the output of the transformer can be designed to meet specific needs.

John Appel

## KEY TERMS

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Ampere

—A standard unit for measuring electric current.

—The variation in time of the flux of a magnetic field through a surface bounded by an electrical circuit generates an electromotive force in that circuit.

Flux

—The flow of a quantity through a given area.

Generator

—A device for converting kinetic energy (the energy of movement) into electrical energy.

Henry

—A standard unit for measuring inductance.

Lenz's law

—The direction of a current induced in a circuit will be such as to create a magnetic field which opposes the inducing flux change.

Mutual inductance

—The ratio of the induced electromotive force in one circuit to the rate of change of current in the inducing circuit.

Right-hand rule (for electric fields generated by changing magnetic fields)

—With the thumb of the right hand along the direction of change of magnetic flux, the fingers curl to indicate the direction of the induced electric field.

Self-inductance

—The electromotive force induced in a circuit that results from the variation with time in the current of that same circuit.

Volt

—A standard unit of electric potential and electromotive force.