Electromagnetic Induction

​Electromagnetic Induction

​Electricity and Magnetism

​Magnetic Effect of current

Electromagnetic Induction

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​# The phenomenon of producing magnetism from electricity is called magnetic effect of the electric current

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​# The phenomenon of producing electric current from magnetism is called electromagnetic induction

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​ Electromagnetic Induction

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​Magnetic Field: The magnetic field is the area around a magnet in which the effect of magnetism is felt.

Magnetic Field Lines: ​Imaginary lines originating from North Pole and entering to south pole.

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​Properties of Magnetic Field Lines:

• The direction of the magnetic field lines is from the south pole to the north pole.

• Magnetic field lines never intersect with each other.

• Magnetic field lines form a closed-loop.

• Field lines have both direction and magnitude at any point on the field

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​Electromagnetic Induction

The phenomenon of producing electric current by induced potential difference or electromotive force (emf) due to changing magnetic field lines passing through a circuit is called electromagnetic induction.

The magnetic field lines passing through a circuit can be changed as follows:

• by moving a magnet to and fro near a coiled conductor,

• by moving the coiled conductor near a magnet, or

• by changing the magnitude of current in the neighbouring circuit

​Faraday's Laws of EMI

​Faraday Concluded the following laws (Observations):

1. ​Whenever there is a change in the number of magnetic field lines passing through the conductor, emf is induced in the conductor

2. The induced emf exists in the circuit so long the change in the magnetic field continues.

3. ​The magnitude of induced emf is directly proportional to the rate of change of the magnetic field through the circuit.

​Fleming's Right hand rule

To use Fleming's Right hand Rule, Note the following:

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Please note that for the change in magnetic field lines in the closed coil, we will try considering the coil is moved instead of the magnet moving.

​Direction of induced current

​The direction of the current due to induced emf can be determined by using Fleming’s right hand rule, which states that: if the thumb, fore finger and the middle finger of right hand are stretched at right angles to each other such that the fore finger indicates the direction of the magnetic field and the thumb shows the direction of motion of the conductor, then the middle finger will indicate the direction of the induced current.

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# The principle of electromagnetic induction is used in devices like electric generators and transformers, so we will look at each device in detail.

Template:

1. What is the device for?

2. Working Principle?

3. Constructions?

4. Workings

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1. Electric Generator: What? Click here. For Text For Video Another Video

   a. AC Generator -Should know

   b. DC Generator​

2. Transformer​

​a.c Generator:

• A generator converts mechanical energy to electrical energy. ​

• a.c generator generates alternating current.​

• Works based on the electromagnetic induction which states that ​ whenever there is a change in the number of magnetic field lines passing through a conductor, voltage is induced in it.

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​Constructions/parts:

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​Armature Coil

Parts:

• An a.c. generator consists of an armature coil made up of several turns of insulated copper wire wound over a soft iron core, strong magnetic field, slip rings and carbon brushes.

• The magnet is concave in shape to produce strong magnetic field. (Radial Magnetic Field)

  Working:

• The armature coil is made to rotate in a strong magnetic field as shown in the previous slide.

• As the coil rotates due to external force such as water in hydropower plant, the number of magnetic field lines passing through the coil changes. Hence an emf or voltage is induced in the circuit.

​Graphical Representation of the induced current/induced emf

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​Graphical Representation of induced emf/current

​Graphical Representation of induced emf/current

• ​As the coil rotates, the number of magnetic field lines passing through the coil continuously changes.

• The number of magnetic field lines passing through the coil is maximum when the coil is perpendicular to the field lines and minimum when the coil is parallel to the field lines.

• The magnitude of the induced emf is maximum when the coil is parallel to the field lines as at that time, the rate of change of the ​magnetic field lines is maximum and the induced emf is minimum when the coil is perpendicular to the field lines owing to the minimum amount of the rate of change of magnetic field lines.

​ Factors affecting induced voltage:

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​ Factors affecting induced voltage:

​The induced voltage depends upon the following:

(a) speed of rotation of the armature coil:- faster the armature coil rotates, greater is the generation of electricity

(b) number of turns of the armature coil:- More the number of turn in the armature coil, larger will be the amount of electricity generated.

(c) strength of the magnetic field:- Stronger the magnetic field, greater is the generation of electricity​

​Name the device above

​ Transformer

​An electrical device used for varying(change) the voltage of an alternating current is called transformer.

​ Transformer

​Transformers are of:

1. Step-Up Transformer-increased the voltage from low to high

2. Step-down Transformer​-decreased the voltage from high to low

​ How does transformer works

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​ Transformer

It works on the principle of electromagnetic induction i.e. whenever there is a change in the number of magnetic field lines in the neighbouring circuit then the voltage is induced in the other circuit. ​

​ Transformer (Sketch)

​ Parts of Transformer

​A transformer consists of two sets of coils:

--a primary coil (P) and a secondary coil(S).

--These coils are wound over a common soft iron core, such that turnings of coils are insulated from each other.

--The core is formed by laminated sheets insulated from each other to reduce the loss of energy as heat.

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Convention

​1. The primary winding is always considered on the left side unless specified and secondary winding on the right side.
2. Voltage is always considered to be fed from left to right.

​ Working of Transformer

​--The input voltage is generally fed into the primary coil and the output voltage is obtained from the secondary coil.

--The alternating current in the primary coil makes it an electromagnet of varying strength, thereby producing magnetic field of varying strength.

--These changing magnetic field lines induce voltage into secondary coil due to electromagnetic induction and the output voltage is obtained.

--The number of turns in both primary coil and secondary coil vary depending on the type of the transformer.

​ Working of Transformer

cont.....
Note: It must be noted that the magnetic field lines passing through the secondary coil is mainly due to the varying magnetic field that the input ac produces in the primary coil. Hence transformer works only with ac not with dc

​ Differences between step up and step down transformer

​ Transformer Ratio

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The ratio of the input voltage to output voltage is equivalent to ratio of number of turns in primary coil to secondary coil is called Transformer ratio.

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​ Transformer Ratio

Multiple Choice

The function of the part labelled X is......

• produce magnetic field.

• induce current in the coil.

• help in rotation of the magnet.

• help in rotation of the armature coil.

Multiple Choice

The resistance of a room heater that draws a current of 2.3A when connected to 230 V mains will be ______________________ Ω.

• 529

• 0.01

• 100

Multiple Choice

Shorter length of a conductor will increase the efficiency of electrical appliances.

• True

• False

Multiple Choice

The output power in a transformer is always obtained in the primary coil.

• True

• Fasle

Multiple Choice

A transformer with X turns in primary coil and Y turns in secondary coil is used to change the magnitude of voltage to 240 V.

Calculate the input voltage and name the type of transformer if Y= 2 X.

• 120V

• 480V

Open Ended

As an obstruction to the flow of electric current, resistance of a wire depends on several factors. Mention TWO ways to have a maximum current flowing through a wire.

Open Ended

To induce voltage, Faraday’s Laws indicate the need to have continuous change in the number of magnetic field lines passing through the armature coil. Therefore, in hydropower plants, the turbines attached to the armature coil of the dynamo is continuously turned using a mechanical energy from the water. Mention TWO ways to increase the generation of electricity.