NEET Study Notes for Electromagnetic Induction and Alternating Current: Electromagnetic Induction is the induction of electromotive force by motion, a conductor across a magnetic field, or by a change in magnetic flux in a magnetic field. The current that changes its magnitude and polarity repeatedly opposite to the direct current is known as alternating current. Alternators are used for the generation of alternating current.

• NEET Physics Syllabus is divided into units from class 11th and class 12th. Electromagnetic Induction and Alternating Current is an important unit from class 12th syllabus with a weightage of around 4%.
• NEET 2022 is expected to be conducted in September 2022. With the study notes for Electromagnetic Induction and Alternating Current, candidates will be able to prepare well for this unit.

Quick Links:

Important Topics in NEET Study Notes for Electromagnetic Induction and Alternating Current

Magnetic Flux

Magnetic Flux is the number of magnetic lines of force that cross a surface Magnetic flux is represented by Φ

where B - the strength of magnetic field

A- area of surface

θ- Angle which is normal to the area made with the direction of magnetic field

S.I. unit of the magnetic field is weber

where 1 weber =108 maxwell

Faraday’s Law of Electromagnetic Induction

Faraday’s Law of Electromagnetic Induction consists of two laws- where emf induction in a conductor is demonstrated by the first law whereas the emf produced in a conductor is quantified.

Faraday’s First Law of Electromagnetic Induction

When the conductor is placed in a varying magnetic field, an electromotive force is induced. Current is induced if the conductor circuit is closed, it is called induced current.

Second Law

The rate of change of flux linkage is equal to the induced emf in a coil.

ε =-N( dφ/dt)

where e is the electromotive force

N represents the number of turns

φ is the magnetic field

Induced EMF

On the changing of the magnetic field that is linked with the circuit, emf will be induced in a circuit. There are three methods to produce induced emf:

• By changing the strength of the magnetic field
• By changing the surface of the area
• By changing the θ

Read NEET Study Notes Gravitation

Lenz’s Law

Heinrich Friedrich Lenz formulated the Lenz’s law that demonstrates the polarity characteristic of the induced emf.

Due to the polarity nature of induced emf, an opposing current is produced that opposes the magnetic field change that is responsible for producing it.

where the negative side is due to the opposing nature of the relationship between induced emf and the reason behind it. This law is similar to the principle of conservation of energy.

Eddy Currents

The changes in magnetic flux induces circulating currents that are formed in the metal. These currents are known as Eddy currents. They are also known as Foucault currents as they were discovered by Foucault. Lenz’s Law helps in the determination of the direction of eddy currents.

Self and Mutual Inductance

Change in the strength of the flow of current is opposed by a characteristic of a coil that is called self-inductance. The coil opposes this by inducing emf

Thus the magnetic flux is directly proportional to the current that flows through the circuit, Mathematically self Inducatnace can be expressed as

ϕ = L I

where L coefficient of self inductance 

Magnetic flux rate of change in the coil is 

Mutual Inductance

The characteristics of a coil by which changes in the flow of current in two coils is opposed by each other through induced emf is called Mutual inductance Mutual Inductance is given by the reaction

Φ=MI, where M is the mutual inductance Rate of change of magnetic flux in coil, is

Mutual Inductance Formula is  

Read NEET Study Notes on Current Electricity

Difference between Self and Mutual Inductance

Alternating Current

The current that opposes its direction in polarity from that of direct current is called Alternating current. Alternating current can also transform the higher voltage to lower voltage and vice versa.

Alternators are one of the main devices that is used for producing alternating current. It can also be produced by a simple method of single-coil AC generator which has magnets with two poles. And a rectangular shape loop wire wherein the mechanical energy is converted into electrical energy.

What is the Average Value of AC?

The average of values of Ac over a cycle is the average value of AC. The average value after a complete cycle is zero. This is due to equal positive and negative life cycles.

Must Read:

• NEET Study Notes on Laws of Motion

• NEET Study Notes on Planar Motion

RMS value of alternating current

When heat effect takes place due to AC power that is equal to DC power, it is termed as RMS value of alternating current.

Impedance and Reactance

Impedance

The ratio of application of emf and current that is produced as a result is called impedance. This takes place in an alternating current circuit. Impedance can be represented by Z. Mathematically Impedance can be represented by

The obstacle that resistance offers along with either inductance or capacitance or both in the flow of circuit is called Impedance. S.I. unit of Impedance is Ohm

Reactance

In an AC circuit, the resistance that is offered by inductance or capacitance or both to the flow of AC is called Reactance. Reactance can be represented by X. Reactance and Impedance is equal when no ohmic resistance acts in the circuit. If this reactance is due to impedance only, it is called impedance reactance. It is represented by X_L whereas the reactance due to capacitance is called capacitative reactance. S.I unit is called Ohm.

Check Books for NEET 2022 Preparation

LC Oscillations

Circuits consist of capacitors and inductors. When charged capacitors are discharged through a non-resistance, electrical oscillations of constant amplitude and frequency are produced. These electrical oscillations are termed LC oscillations.

The electrical charge that a capacitor store is an initial charge. It is denoted by

There is zero charges in the inductor circuit whereas, in a sine wave, the current varies with respect to time.

Working of LC

On turning the switch on, there is an increase in the current flowing through the circuit, however the charge on the capacitor keeps decreasing, A magnetic field is produced inside the inductor due to this induced current. The magnetic field at a point when an electric current is the maximum in the circuit is UB=12LIm

The magnetic field starts to decrease with time as there are no changes in the inductors. An induction of current is caused due to this decrease in the magnetic field. Induced current has the opposite polarity. This current flows in the opposite direction. This leads to capacitor charging. On the capacitor charging at its maximum, the entire procedure repeats itself.

These oscillations of the current flow in the circuit from the capacitor to the inductor and back to the capacitor are LC Oscillations. These oscillations occur with a frequency that is derived by application of Kirchoff’s law

Power in AC Circuit

The rate at which work is done in the circuit is called power. The current and emf are not equal.P= IV, where I is the current that flows through the circuit, V- voltage across the circuit.

Power Factor

The ratio of the power flowing through the circuit and the apparent power present in the circuit is called the power factor. The power factor is dimensionless. It ranges from -1 to 1. It can be denoted by

Power Factor= True Power/ Evident Power

, cos ø= R/Z

where R is the resistance in the circuit, Z is the hindrance of the circuit

In a capacitative circuit, the Power factor is 0 while in a resistive circuit, it is 1

AC generator and Transformer

AC Generators convert mechanical energy to a form of electrical energy called alternating current. These are also called alternators. The unit for a rating of AC Generators is Kilo volt-amperes.

• AC Generators are of two types- Synchronous and Induction Generators. The working of the AC Generator is based on electromagnetic induction.
• The length of the rotating wire determines the emf of the AC generator. With an increase in the number of turns, emf also increases.
• AC Generators also have the advantage that the maintenance is less.

Read:

• NEET Study Notes on Ray Optics
• NEET Study Notes on Wave Optics

Transformer

Transformer is responsible for transforming the alternating voltage from a greater to a smaller value or vice versa. The workings of the transformer are based on mutual induction.

• A magnetic flux connects the two circuits based on the principle of mutual inductance.
• The two coils- primary and secondary coil, are separated from each other but reluctance ensures that the path is magnetically linked.
• Transforms are of two types- Step up and Step down transformer. Step-up transformer transforms low to high voltage whereas the step-down transformer transforms high voltage to low voltage.
• DC Transformers help in preventing Direct current to the next circuit.

NEET Sample MCQs on Electromagnetic Induction and Alternating Current

Question: In what way does the direction and magnitude changes in alternating current?

1. Exponentially
2. Does not vary
3. Randomly
4. Periodically

Answer: Periodically

Question: What do step transformers do?

1. Decrease voltage
2. Decrease electrical power
3. Increase electrical power
4. Increase Voltage

Answer: Increase in Voltage

Question: On which of the following conservation, Lenz law is based?

1. Energy
2. Momentum
3. Charge
4. Mass

Answer: Energy

Question: What happens to impedance at resonance?

1. Purely capacitance
2. Purely resistive
3. Purely inductive
4. None of the above

Answer: Purely resistive

Question: Why is the transformer core laminated?

1. Reduces cost
2. Simplify construction
3. Minimize eddy current loss
4. Reduce Hysteresis Loss

Answer: Minimize eddy current loss

Quick Links: