L-10

ELECTROMAGNETISM

Dept. of E&E, MIT, Manipal1

ELE1001: Basic Electrical Technology

Dept. of E&E, MIT, Manipal2

ELE1001: Basic Electrical Technology

Objective

To conceptualize the basic laws in electromagnetism.

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ELE1001: Basic Electrical Technology

Contents Introduction Flux produced by a current carrying conductor Magnetic field produced by a solenoid Force acting on a conductor Direction of Force: Fleming’s left hand rule Faraday’s laws of Electromagnetic Induction Lenz’s law Direction of induced emf :

Fleming's right hand rule Dynamically induced emf Statically induced emf

Introduction

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• Electromagnetism defines the relationship between magnetism and electricity.

• Electric generator, motors, transformers, etc. work based on the principle of electromagnetic induction

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5

Flux produced by a current carrying conductorAn electric current flowing in a conductor creates a magnetic field around it.Determination of direction of magnetic field:Maxwell’s right hand grip rule :

Assume that the current carrying conductor is held in right hand so that the fingers wrap around the conductor and the thumb is stretched along the direction of current. Wrapped fingers will show the direction of circular magnetic field lines.

.+

ELE1001: Basic Electrical Technology

Dept. of E&E, MIT, Manipal

6

Right hand grip rule for solenoid:

If the coil is gripped with the right hand, with the fingers pointing in the direction of the current, then the thumb, outstretched parallel to the axis of the solenoid, points in the direction of the magnetic field inside the solenoid

Magnetic field produced by a solenoidDetermination of direction of magnetic field:

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ELE1001: Basic Electrical Technology

Force acting on a conductor

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A current carrying conductor, placed in a magnetic field, experiences a force.

This is the principle of electric motor.

Force on a single conductor = flux density length of conductor current

f = B I l sinθ Newton This force can be increased by

increase in any one of these components.

ELE1001: Basic Electrical Technology

θ

θ

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Direction of Force: Fleming’s left hand rule

Field

(Mechanical force)

Current(Second finger)

thumb

(First finger)

ELE1001: Basic Electrical Technology

Let the thumb, first finger and second finger of the left hand be extended such that they are all at right-angles to each other.

If the first finger points in the direction of the magnetic field, the second finger points in the direction of the current, then the thumb will point in the direction of the motion of the conduct

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dtdNe

ELE1001: Basic Electrical Technology

Faraday’s laws of Electromagnetic Induction

An induced emf is set up whenever the magnetic field linking that circuit changes.

The magnitude of the induced emf in any circuit is proportional to the rate of change of the magnetic flux linking the circuit.

An electro magnetically induced emf always acts in such a direction to set up a current opposing the motion or change of flux responsible for inducing the emf.

Dept. of E&E, MIT, Manipal10

ELE1001: Basic Electrical Technology

Lenz’s law

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Direction of induced emf :Fleming's right hand rule

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If the first finger of the right hand is pointed in the direction of the magnetic flux, and if the thumb is pointed in the direction of motion of the conductor relative to the magnetic field, then the second finger, held at right angles to both the thumb and the first finger represents the direction of emf.

ELE1001: Basic Electrical Technology

The voltage induced in the conductor due to relative motion of conductor and magnetic field

Either conductor or magnetic field is moving

Principle of Electric generator

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sinBlve

ELE1001: Basic Electrical Technology

Dynamically induced emf

The voltage induced in the conductor due to change in the magnetic field

Conductor is stationary

Magnetic Field is changing in a stationary Magnetic System;

Eg: Transformer

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ELE1001: Basic Electrical Technology

Statically induced emf

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Summary

An electric current flowing in a conductor creates a magnetic field around it.

A current carrying conductor, placed in a magnetic field, experiences a force. (eg. motor).

Whenever the magnetic field linking with a circuit changes an emf is induced in it. Change in magnetic field can be achieved statically (eg. transformer) or by dynamically (eg. generator).

ELE1001: Basic Electrical Technology