KCET Moving Charges and Magnetism Topics 2025

KCET Moving Charges and Magnetism Topics 2025 include Magnetic Force, Motion in a Magnetic Field, The Solenoid, Torque on the Current Loop, and Magnetic Dipole. This chapter is entirely based on how the magnetic field associates with charged particles (moving) such as protons, electrons, and current-carrying wires. KCET Moving Charges and Magnetism Weighatge 2025 is expected to be 2 to 3 questions carrying approximately 6 to 9 marks in the KCET 2025 Question Paper. The KCET Moving Charges and Magnetism Questions are asked in the form of MCQs. For every correct answer, candidates will be awarded 1 mark and there is no provision for negative marking for wrong answers. In this article, we have discussed the KCET 2025 Moving Charges and Magnetism Topics, sample questions, weightage, etc. 

What is Moving Charges and Magnetism in KCET 2025?

The alignment of a needle in a compass led to an interesting discovery about how electricity and magnetism are related. Researchers found that the needle points in a certain direction, which can be imagined as a tangent to an invisible circle around a straight wire placed in the centre. Normally, the needle stays in this position, but when electricity flows through the wire, the needle moves to a different angle. This movement happens because the electric current creates a magnetic field. The way the needle deflects is explained by a simple rule known as Ampere’s swimming rule, which helps us understand the direction of this magnetic influence.

KCET Moving Charges and Magnetism Topics 2025

Here are the topics covered in KCET 2025 Moving Charges and Magnetism.

• Introduction to Moving Charges and Magnetism
• Magnetic Force
• Motion in a Magnetic Field
• Magnetic Field due to a Current Element, Biot-Savart Law
• Magnetic Field on the Axis of a Circular Current Loop
• Ampere’s Circuital Law
• The Solenoid
• Force between Two Parallel Currents, the Ampere
• Torque on Current Loop, Magnetic Dipole
• The Moving Coil Galvanometer

1. Ampere’s Swimming Rule

According to the rule, imagine a swimmer swimming along a wire in the direction of the electric current, facing the compass needle. The needle’s north pole would be deflected to the left.

2. Magnetic Field

A stationary charge creates an electric field, while a moving charge generates a magnetic field, represented by the letter B. The shape of this field changes depending on the shape of the conductor carrying the current. 

3. Motion of Charged Particles in a Magnetic Field

When a charged particle (like an electron) moves in a magnetic field, it experiences a force described by the equation: 

\[F = qvB \sin θ\]

Here, F is the force, q is the charge, v is the speed, B is the magnetic field, and θ is the angle between the speed and the magnetic field. Since this magnetic force is always perpendicular to the motion, it doesn’t affect the particle's speed or energy. 

• Case 1 If the angle θ is 0° or 180° (the particle moves parallel to the magnetic field), it will keep moving in a straight line. Case 1: θ = 00 0r 1800
• Case 2 If θ is 90° (the particle moves perpendicular to the magnetic field), it will move in a circular path. The magnetic force acts as a centripetal force, keeping the particle in that circle. Case 2: θ = 900

4. Biot-Savart Law

Biot-Savart Law helps us understand how a small segment of a current-carrying wire creates a magnetic field at a point nearby. The magnetic field produced depends on the current, the length of the wire segment, and how far away you are from it. 

5. Ampere’s Circuital Law

Ampere’s Circuital Law states that the total magnetic field around a closed loop is proportional to the total current flowing through that loop. You can think of it as a way to calculate the magnetic field created by currents in various configurations.

6. Magnetic Field from a Straight Current-Carrying Wire

When you have a long, straight wire carrying current, you can use Ampere's Law to find the magnetic field around it:

 \[B = \frac{μ_0 I}{2 \pi r}\] 

7. Magnetic Field Due to a Solenoid

A solenoid is a long coil of wire. When electric current passes through it, it produces a strong and uniform magnetic field inside.

KCET 2025 Moving Charges and Magnetism Questions

1. (a) A circular coil of 30 turns and radius 8.0 cm carrying a current of 6.0 A is suspended vertically in a uniform horizontal magnetic field of magnitude 1.0 T. The field lines make an angle of 60° with the normal of the coil. Calculate the magnitude of the counter torque that must be applied to prevent the coil from turning.

(b) Would your answer change, if the circular coil in (a) were replaced by a planar coil of some irregular shape that encloses the same area? (All other particulars are also unaltered.)

Ans.4.13

2. Two concentric circular coils X and Y of radii 16 cm and 10 cm, respectively, lie in the same vertical plane containing the north-to-south direction. Coil X has 20 turns and carries a current of 16 A; coil Y has 25 turns and carries a current of 18 A. The sense of the current in X is anticlockwise, and clockwise in Y, for an observer looking at the coils facing west. Give the magnitude and direction of the net magnetic field due to the coils at their centre.

Ans.4.14

3. A magnetic field of 100 G (1 G = 10–4 T) is required which is uniform in a region of linear dimension about 10 cm and area of cross-section about 10–3 m2. The maximum current-carrying capacity of a given coil of wire is 15 A and the number of turns per unit length that can be wound round a core is at most 1000 turns m–1. Suggest some appropriate design particulars of a solenoid for the required purpose. Assume the core is not ferromagnetic.

Ans.4.15

4. A toroid has a core (non-ferromagnetic) of inner radius 25 cm and outer radius 26 cm, around which 3500 turns of a wire are wound. If the current in the wire is 11 A, what is the magnetic field (a) outside the toroid, (b) inside the core of the toroid, and (c) in the space surrounded by the toroid?

Ans.4.17

5. Answer the following questions:

(a) A magnetic field that varies in magnitude from point to point but has a constant direction (east to west) is set up in a chamber. A charged particle enters the chamber and travels undeflected along a straight path with constant speed. What can you say about the initial velocity of the particle?

(b) A charged particle enters an environment of a strong and non-uniform magnetic field varying from point to point both in magnitude and direction and comes out of it following a complicated trajectory. Would its final speed equal the initial speed if it suffered no collisions with the environment?

(c) An electron travelling west to east enters a chamber having a uniform electrostatic field in north to south direction. Specify the direction in which a uniform magnetic field should be set up to prevent the electron from deflecting from its straight-line path.

Ans.4.18

6. A magnetic field set up using Helmholtz coils (described in Exercise 4.16) is uniform in a small region and has a magnitude of 0.75 T. In the same region, a uniform electrostatic field is maintained in a direction normal to the common axis of the coils. A narrow beam of (single species) charged particles all accelerated through 15 kV enters this region in a direction perpendicular to both the axis of the coils and the electrostatic field. If the beam remains undeflected when the electrostatic field is 9.0 × 10–5 V m–1, make a simple guess as to what the beam contains. Why is the answer not unique?

Ans.4.20

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