Electromagnetic Induction is used to Electromagnetic Induction is used to generate most of the electrical energy generate most of the electrical energy

used todayused today

• The production of electricity by magnetism is called electromagnetic induction.– Michael Faraday first demonstrated

that magnetism can produce electricity.

– Faraday showed that when a magnet approaches a coil, a current is induced in the coil.

– The direction of induced current depends on the pole of the magnet that approaches the coil.

– A stationary magnet will not induce current. There must be motion of the coil or magnet to induce current.

• Faraday’s law of electromagnetic induction: A changing magnetic field in the region of a closed-loop conductor will induce an electric current.

A galvanometer is a sensitive current detector. This diagram illustrates electromagnetic induction. As the magnet is moved into the wire coil, current is generated in the coil.

• A wire moving in a magnetic field produces electromotive force (emf).

– Electromagnetic induction also involves the production of electric potential difference (emf).

– Faraday discovered that three factors influence the magnitude of emf and induced current in the wire:– The velocity of the wire – the higher

the velocity, the greater the emf and current.

– The strength of the magnetic field – the stronger the magnetic field, the greater the emf and current.

– The length of the wire in the magnetic field – the longer the wire, the greater the emf and current.

A segment of a closed loop of wire moves through a magnetic field. Note that the wire must be perpendicular to the magnetic field in order for current and emf to be induced.

• Lenz’s law states that induced current and emf are in a direction that opposes the change that produced them.

– Lenz’s law means that induced current creates a magnetic force that acts on the wire. This force always opposes the wire. Lenz’s law thus obeys the law of conservation of energy – it takes work to produce energy in a different form.

Holding the hand flat will determine the following variables:

Thumb: direction of velocity of wire

Fingers: direction of magnetic field

Palm: direction of induced conventional current

• Lenz knew the cardinal rule…– That nature likes to conserve things (like energy) – you can’t

get something for free

• So he reasoned that…“The induced current is such as to OPPOSE the CHANGE

in applied magnetic field.”

This is Lenz’s Law

• Originally, when the magnet is not moving, the magnetic field is not changing.

• Suddenly, the magnet moves towards the coil and the field starts to increase.

• The current in the coil instantly starts up to counteract this increase.

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• Right-Hand Rule for Induction in SolenoidsAccording to Lenz’s law, the induced current created by pushing a permanent magnet into a solenoid will create a magnetic field in the solenoid. The magnetic field creates a repulsive force against the permanent magnet.

Holding the right hand with the fingers curled and the thumb extended will determine the following variables:

• The thumb points in the direction of the north pole of the solenoid.

• Fingers curl in the direction of induced current.

• As the magnet approaches the loop, the applied magnetic field in the centre increases. This is a change.

• An Induced Field is created which attempts to cancel the applied field – to keep the total field at zero – its original value.

• This induced field must be a associated with a current – the INDUCED CURRENT in the loop. You can determine the direction of the current by the RHR.

Determine the direction of the induced current in the solenoid shown below.