Plus Two Physics Chapter Wise Previous Questions Chapter 4 Moving Charges and Magnetism is part of Kerala Plus Two Physics Chapter Wise Previous Questions and Answers Kerala. Here we have given Plus Two Physics Chapter Wise Questions and Answers Chapter 4 Moving Charges and Magnetism.

## Kerala Plus Two Physics Chapter Wise Previous Questions and Answers Chapter 4 Moving Charges and Magnetism

Question 1.

Two charged particles q_{1} and q_{2} are moving through a uniform magnetic field (B) as shown in figure:** [March-2018]
**a. What is the shape of path of q

_{1 }and q

_{2}.

b. Derive an expression for cyclotron frequency with the help of a neat diagram.

Answer:

a.

q

_{1 }– helix

q

_{2}– circular

b. Magnetic field out of the paper.

Cyclotron uses the fact that the frequency of revolution of the charged particle in a magnetic field is independent of its

energy. The particles move most of the time inside two semicircular disc-like metal containers, D

_{1}and D

_{2}, which are called dees.

The whole assembly is evacuated to minimise collisions between the ions and the air molecules. A high frequency alternating voltage is applied to the dees. Positive ions or positively charged particles (e.g., proton) are released at the centre P. They move a semi-circular path in one of the dees and arrive in the gap between the dees in a time interval T/2; where T, the period of revolution, is given

T = 1/ υ

_{c}= 2πm/qB

υ

_{c}= qB / 2πm. This frequency is called the cyclotron frequency for obvious reasons and is denoted by υ

_{c}.

Question 2.

An electric charge q is moving with a velocity v in the direction of a magnetic field B. The magnetic force acting on the charge is

i. qvB

ii. zero

iii.

iv.

**OR**

Starting from Biot – Savart law, obtain an expression for the magnetic field at an axial point of a circular coil carrying current.

**OR
**a. An ammeter is a current measuring device which is always connected in an electric circuit.

b. Describe a cyclotron and obtain an expression for cyclotron frequency.

**[March-2017]**

Answer:

a. Zero (F = qvBsinθ, θ=0,

sinθ= 0,F = 0 )

b.

)

**OR**

a. Series

b.

- Cyclotron is a high energy particle accelerator.
- Magnetic field out of the paper.

Cyclotron uses the fact that the frequency of revolution of the charged particle in a magnetic field is independent of its

energy. The particles move most of the time inside two semicircular disc-like metal containers, D_{1} and D_{2} , which are called dees.

The whole assembly is evacuated to minimise collisions between the ions and the air molecules. A high frequency alternating voltage is applied to the dees. Positive ions or positively charged particles (e.g., proton) are released at the centre P. They move a semi-circular path in one of the dees and arrive in the gap between the dees in a time interval T/2; where T, the period of revolution, is given

T = 1/ υ_{c} = 2πm/qB

υ_{c} = qB / 2πm. This frequency is called the cyclotron frequency for obvious reasons and is denoted by υ_{c}.

Question 3.

A moving charge can produce a magnetic field.

a. How does a current loop behaves like a magnetic dipole ?

b. Draw the magnetic field lines for a current loop to support your answer.

c.

(i) What is a cyclotron ?

(ii) Write down the expression for cyclotron frequency. **[March-2016]
**Answer:

a. One face north and other face south, i.e

b.

c.

(i) Cyclotron is a high energy particle accelerator.

(ii)

Cyclotron uses the fact that the frequency of revolution of the charged particle in a magnetic field is independent of its

energy. The particles move most of the time inside two semicircular disc-like metal containers, D

_{1}and D

_{2}, which are called dees.

The whole assembly is evacuated to minimise collisions between the ions and the air molecules. A high frequency alternating voltage is applied to the dees. Positive ions or positively charged particles (e.g., proton) are released at the centre P. They move a semi-circular path in one of the dees and arrive in the gap between the dees in a time interval T/2; where T, the period of revolution, is given

T = 1/ υ

_{c}= 2πm/qB

υ

_{c}= qB / 2πm. This frequency is called the cyclotron frequency for obvious reasons and is denoted by υ

_{c}.

Question 4.

A current carrying wire produces a magnetic field in its surrounding space.

i. The S.i. unit magnetic flux density is

(a) henry

(b) tesla

(c) Am^{2}

(d) A^{m
}ii. With the help of a diagram, derive an expression for the magnetic field at a point on the axis of a circular current loop.

iii. Consider a tightly wound 100 turn coil of radius 10 cm, carrying a current of 1 A. What is the magnitude of the magnetic field at the centre of the coil ? **[March-2015]
**Answer:

i.b. tesla.

The magnetic field at P due to current element dl is

Question 5.

The relation between magnetic field and current is given by Biot-Savart law.

a. Illustrate Biot-Savart law with necessary figure.

b. Compare Biot-Savart law with Coloumb’s law for electrostatic field.

c. Give an expression for magnetic field on the axis of a circular current loop. (Expression only)

d. What is the value of B at the centre of the loop? ** [March-2014]
**Answer:

**a.**

According to this law the small magnetic field dB at the point P is a current I, length of that element dl and sin of the angle between element in the direction of current and the line joining the element point inversely proportional to the square of the distance from the element to the point P.

where is proportionality constant.

**b. Similarities:
**1. Both deal with large range forces.

2. In both, force

3. In both, principle of superposition can be applied to the fields.

**Differences:
**1. Magnetic field is produced by a vector source. Electrostatic field by a scalar source.

2. Magnetic field is perpendicular to the plane of position vectors. Electrostatic field is along the position vector

Question 6.

Ampere’s circuital theorem is used to determine the magnetic field produced by a current carrying conductor.

a. State Ampere’s circuital theorem.

b. Using the theorem obtain the expression for magnetic field produced by an infinitely long straight conductor carrying current.

c. Drive the expression to find the force per unit length between two long straight parallel wires carrying currents.

**[Feb-2014]
**Answer:

a. The line integral of a magnetic field around a dosed loop is p0 times the current enclosed by the loop.

b. Consider a conductor of infinite length.

c. Magnetic field due to current I,

Question 7.

Force acting on a charged particle when it moves in a combined electric and magnetic field is known as Lorentz force. A rectangular loop carrying a steady current is placed in a uniform magnetic field. Obtain the expression for the force acting on the loop. ** [March-2013]
**Answer:

A rectangular loop carrying a steady current I and placed in a uniform magnetic field experiences a torque. It does not experience a net force.

Consider a rectangular coil ABCD, placed in a uniform magnetic field, B. Then, τ=l ab B = NIAB sin e or, where A is the area of the coil, N is the no of turns. Here M = I (NA) is called

magnetic dipole moment. If θ =0 or 180, τ=0.

Question 8.

Oersted found that moving charges or current produce a magnetic field in the surrounding space.

a. An electric current is flowing due south along a power line. What is the direction of magnetic field

(i) above it

(ii) below it

b. Draw a neat and labelled diagram of a cyclotron. State the underlying principle of its working.

c. A cyclotron’s oscillator frequency is 10 MHz. What should be the operating magnetic field for accelerating protons? **[Model-2012]
**Answer:

a.

(i) West

(ii) East

b.

It is a device used to accelerate charged particles like protons, deuterons, α particles, etc., to very high energies. Magnetic field out Deflection plate of the paper

**Principle:** A charged particle can be accelerated to very high energies by making it pass through an electric field and a perpendicular magnetic field which throws the charged particle into a circular motion. The frequency does not depend on the speed of the particle and the radius of the circular orbit.

**Working:** Suppose a proton enters the gap between the two dees.

- In the first half cycle let D
_{1}be negative so the particle accelerates towards Dr. As it enters D, it follows a circular path due to the perpendicular magnetic field. - At the instant the proton comes out of D
_{1}, D2 becomes negative and’it accelerates towards D2 and follows a circular path inside it. - This process repeats and the proton finally attains very high energy.
- The accelerated proton is ejected through a window and hits the target. The frequency of the revolution of

the particle will be: (cyclo litm tron frequency)

Let is the velocity of the particle when it comes out of the cyclotron. Then its energy is given by

c.

Question 9.

You are sitting in a room in which a uniform magnetic field 1? exists. At the centre of the room a charged particle is suddenly projected horizontally and it starts circular motion in the horizontal plane.

a. What should be the direction of the magnetic field for this to happen?

b. Will there be a change in kinetic energy of the particle due to this circular motion? Why?

c. A cyclotron uses a magnetic field and an electric field to increase the. energy of a charged particle. Describe its construction and working. **[March-2011]
**Answer:

a. Perpendicular.

b. No, magnitude of velocity is same.

c.

It is a device used to accelerate charged particles like protons, deuterons, α particles, etc., to very high energies. Magnetic field out Deflection plate of the paper

**Principle:** A charged particle can be accelerated to very high energies by making it pass through an electric field and a perpendicular magnetic field which throws the charged particle into a circular motion. The frequency does not depend on the speed of the particle and the radius of the circular orbit.

**Working:** Suppose a proton enters the gap between the two dees.

- In the first half cycle let D, be negative so the particle accelerates towards Dr. As it enters D, it follows a circular path due to the perpendicular magnetic field.
- At the instant the proton comes out of D, D2 becomes negative and’it accelerates towards D2 and follows a circular path inside it.
- This process repeats and the proton finally attains very high energy.
- The accelerated proton is ejected through a window and hits the target. The frequency of the revolution of

the particle will be: (cyclo litm tron frequency)

Let is the velocity of the particle when it comes out of the cyclotron. Then its energy is given by

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