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# NCERT Exemplar Class 12 Physics Chapter 4 Solutions: Moving Charges and Magnetism

NCERT Exemplar Class 12 Physics Solutions Chapter 4 – Moving Charges and Magnetism will help you learn about topics like the magnetic field, the direction of circular coil, magnetic force, etc. Practising these concepts with NCERT Exemplar Class 12 Physics will not only help you manage a good score in CBSE class 12 board exams but also play a crucial role in toughest competitions like JEE and NEET.

There are 29 NCERT Exemplar problems with the coherent coverage of each topic in this chapter. The questions are of different types ranging from MCQ type to long-answer type where you will be required to have a better understanding of concepts like a magnetic force between two parallel currents, moving coil galvanometer, cyclotron, torque on current-carrying loop, solenoid, etc. We have provided complete solutions for all the NCERT Exemplar problems for class 12 physics chapter 4 in a stepwise manner.

## Important Topics for NCERT Exemplar Class 12 Physics Solutions Chapter 4 – Moving Charges and Magnetism

NCERT Exemplar Class12 Physics Solutions Chapter 4- Moving Charges and Magnetism deals with moving charges and magnetism. Students will be given knowledge, how magnetic fields exert a force on moving charged particles, these charged particles are nothing but electrons, protons and current-carrying wires. Moving charges and current wires produces a magnetic field in a space

• Magnetic Force on a Current-Carrying Wire

Each wire creates a magnetic field that exerts a force on other current-carrying wire. This will cause the wires to be attracted or repelled from each other. Thus this force in the direction given by right -hand rule 1 is said to be a magnetic force on a current-carrying wire.

F = qvB sin θ, where v is a drift velocity

•     Biot Savart Law:

It’s a mathematical expression that demonstrates the magnetic intensity at any point due to a steady current in an infinitely long wire is directly proportional to current and inversely proportional to the distance from a point to the wire.

B = μ0/4π∫IdlSinθ/r2

•     Velocity Selector:

Velocity selector is an arrangement of electric and magnetic fields perpendicular to each other. As its name implies it allows charged particles to enter the region with a certain velocity.

V = EB

•     Torque on a Current-Carrying Loop:

When the current is passed through the loops, the magnetic field exerts a torque (a twisting force around the axis) on the loops which rotates the shaft.

Torque about the axis= τ = IAB.

•     Cyclotron :

A cyclotron is a device used to accelerate the charged particles. It was devised by Lawrence, it works on the principle that charge is moving perpendicular to the magnetic field which creates a circular path.

Cyclotron frequency = ωc = qB/m    & Cyclotron radius =ωc = qB/m

•     Moving Coil Galvanometer:

It’s an electromagnetic device which measures small values of current. This device works on the principle that when a current-carrying loop is placed in an external magnetic field which experiences a torque, determined by changing the values of current.

## Exercise Discussion of NCERT Exemplar Class 12 Physics Solutions Chapter 4 – Moving Charges and Magnetism

• The first two sections of the NCERT Exemplar problems are of MCQ types that test your knowledge on the concepts of the moving charged particles.
• The first 11 NCERT Exemplar problems are generally from concepts like Biot Savart law, current-carrying loop, velocity selector, cyclotron, ampere’s law etc.
•  The next section comprises very short type questions, containing 4 questions. Questions 4.12 and 4.15 uses a concept of cyclotron frequency.
• The next section is a short answer type section, containing 6 questions. These questions are quite tough compared to MCQ and VSA type. Question 4.21 is about the construction of a multi-range voltmeter using a galvanometer circuit. Voltmeter ratings are given and resistance is to be measured.
• The last section, long answer type, contains 7 questions and questions generally use a concept of torque on a current-carrying rectangular loop.

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• The NCERT Exemplar problems and solutions for CBSE class 12 physics chapter 4 at Instasolv are free of cost and will help you use your time effectively.
• Instasolv experts realize how easy solutions provide to you to gain maximum knowledge of the concepts and hence have provided easy explanations.
• These NCERT Exemplar Class 12 Physics Solutions Chapter 4 – Moving Charges and Magnetism will help you to study more and appear in different competitive exams and CBSE class 12 board exams with full confidence.
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