HC Verma Class 12 Physics Solutions Chapter 39: Alternating Current

About the chapter: HC Verma Solutions Class 12 Physics Chapter 39

The Alternating Current

Alternating current strength keeps changing over time, and its direction changes every so often.

Average Value of Alternating Current: The mean or average value of alternating current over any half cycle is the value of steady current that would send the same amount of charge through a circuit in the time of a half cycle (i.e. T/2) as alternating current sends through the same circuit in the same time.

• AC Circuit With Only Resistance: Connect a source of alternating e.m.f. to a pure resistance R.
• AC Circuit With Only Inductance: In an a.c. circuit with only inductance, the alternating current I is 90 degrees behind the alternating voltage E, or by one-fourth of a period. On the other hand, the voltage across L is 90 degrees ahead of the current.
• AC Circuit With Only Capacitance: Let a source of alternating e.m.f. be connected to a capacitor with only capacitance C.

AC Dynamo AC Generator

An alternating current generator or dynamo is a machine that turns mechanical energy into alternating current energy. It is one of the most important ways that electromagnetic induction can be used. Nikola Tesla, a scientist from Yugoslavia, came up with the idea for the generator. The word “generator” is wrong because the machine doesn’t make anything. It is actually an alternator that changes one kind of energy into another.

Principle:

An alternating current generator or dynamo is based on electromagnetic induction. This means that when the amount of magnetic flux linked to a coil changes, an e.m.f. is induced in the coil. It lasts as long as there is a change in the magnetic flux going through the coil. Fleming’s right-hand rule shows the direction of the current that is caused.

Theory and How It Works:

As the armature coil turns in the magnetic field, the angle between the field and the normal coil keeps changing. So, the magnetic flux that the coil is linked to changes. In the coil, an e.m.f. is made.

Transformer

A step-up transformer is a type of transformer that boosts the AC voltage. A step-down transformer is a type of transformer that lowers the voltages of alternating current.

Principle:

Mutual induction is the idea behind how a transformer works. This means that when the amount of magnetic flux linked to one coil changes, an e.m.f. is induced in the coil next to it.

Construction:

A transformer has a rectangular core made of laminated sheets of soft iron that are well separated from each other.

Loss of Energy in a Transformer:

Here are the main ways that a transformer loses energy:

• Copper loss is the loss of energy in the form of heat in a transformer’s copper coils. This is because Joule heats up the wires that carry electricity. These are kept to a minimum with thick wires.
• Iron loss is the loss of energy as heat in the transformer’s iron core. This is because of eddy currents that form in the iron core. Taking laminated cores cuts down on it.
• Even with the best insulation, magnetic flux can leak out. So, the rate of change of magnetic flux linked to each turn of S1S2 is less than the rate of change of magnetic flux linked to each turn of P1P2. It can be lessened by winding the primary coil over the secondary coil.
• Loss of hysteresis. This is the loss of energy that happens when the iron core is repeatedly magnetized and unmagnetized by the a.c. Using a magnetic material with a low hysteresis loss keeps the loss to a minimum.
• Magnetostriction is also known as a transformer’s humming sound.
• So, the power that comes out of the best transformer may be about 90% of the power that goes into it.

Consequences of Displacement Current

The discovery of displacement current is very important because it shows that the rules of electricity and magnetism are the same. Faraday’s law of electromagnetic induction says that the size of the emf that is created in a coil is equal to the rate of change of the magnetic flux that is linked to it. Since the emf between two points A and B is a measure of how much work it takes to move one unit of charge from A to B, the presence of an emf shows that there is an electric field. Because of this, Faraday came to the conclusion that a magnetic field that changes over time creates an electric field.

Maxwell’s idea is that an electric field that changes over time gives rise to displacement current, which also makes a magnetic field like conduction current. In fact, it is the symmetrical opposite of Faraday’s idea, which led Maxwell to think that the displacement current is also a source of the magnetic field. It means that as the electric and magnetic fields change over time, they cause each other to change. Based on these ideas, Maxwell came to the conclusion that electromagnetic waves exist in places where the electric and magnetic fields change over time.

How strong an electromagnetic wave is:

An electromagnetic wave’s intensity at a point is measured by the amount of energy that crosses per second per unit area around that point as the wave moves.

Electromagnetic Spectrum:

After Hertz found electromagnetic waves through experimentation, many other types of electromagnetic waves were found through different ways of making them move.

The electromagnetic spectrum is the orderly spread out of electromagnetic waves based on their wavelength or frequency.

Electromagnetic spectrum main parts:

In a broad sense, the electromagnetic spectrum can be divided into the following main parts, which are listed in order of increasing frequency.

Microwaves:

Microwaves are radio waves with a frequency between 1 GHz and 300 GHz. They are made of vacuum tubes with special parts. Among them are klystrons, magnetrons, Gunn diodes, and so on. 

Uses:

• Radar systems, which help planes find their way, use microwaves.
• A radar that uses a microwave can find out how fast a moving tennis ball, cricket ball, or car is going.
• People use microwave ovens to cook food.
• Microwaves are used to watch the movement of trains on rails from control rooms where microwaves are used.

How X-rays are used

• In surgery to find broken bones, foreign objects like bullets, sick organs, and stones in the body.
• In engineering, they are used to find flaws, cracks, holes, and other problems in finished metal products. For putting welding, casting, and molds to the test.
• In radiotherapy, to treat skin diseases that can’t be found and cancerous growths.
• Police departments find explosives, opium, gold, and silver on the bodies of people who are trying to smuggle them.
• In the business world, it is used to find pearls in oysters, flaws in rubber tyres, gold, tennis balls, etc. To check how evenly insulating materials are made.
• In scientific research, this is used to study how atoms and molecules are arranged in complex substances and how crystals are made. 

HC Verma Class 12 Physics Part 2 Complete Syllabus

• Chapter 23 – Heat and Temperature
• Chapter 24 – Kinetic Theory of Gases
• Chapter 25 – Calorimetry
• Chapter 26 – Laws of Thermodynamics
• Chapter 27 – Specific Heat Capacities of Gases
• Chapter 28 – Heat Transfer
• Chapter 29 – Electric Field and Potential
• Chapter 30 – Gauss’s Law
• Chapter 31 – Capacitors
• Chapter 32 – Electric Current in Conductors
• Chapter 33 – Thermal and Chemical Effects of Current
• Chapter 34 – Magnetic Field
• Chapter 35 – Magnetic Field due to a Current
• Chapter 36 – Permanent Magnets
• Chapter 37 – Magnetic Properties of Matter
• Chapter 38 – Electromagnetic Induction
• Chapter 39 – Alternating Current
• Chapter 40 – Electromagnetic Waves
• Chapter 41 – Electric Current through Gases
• Chapter 42 – Photoelectric Effect and Wave-Particle Duality
• Chapter 43 – Bohr’s Model and Physics of Atom
• Chapter 44 – X-rays
• Chapter 45 – Semiconductors and Semiconductor Devices
• Chapter 46 – The Nucleus
• Chapter 47 – The Special Theory of Relativity

Features of Utopper HC Verma Solutions Class 12 Physics Chapter 39

• Students can solve similar problems on their own with the help of HC Verma’s answers in the Utopper.
• Students are given answers that are correct and easy to understand.
• The solutions are given to match the level of understanding of a student in that class.
• The HC Verma solutions that Utopper gives the answer to and explains all of the questions in each chapter.