# Assertion Reason Physics Chapter 4 Moving Charges and Magnetism

Questions of Assertion Reason of Physics Chapter 4 Moving Charges and Magnetism CBSE Class 12 are very simple to understand as this chapter deals with Moving Charges and Magnetism To solve assertion reason type questions of Physics, a deeper understanding of concept about 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 and The Moving Coil Galvanometer is required. In order to help the student in solving Assertion Reason type of questions, detailed process is explained.

How to solve Assertion Reason Type Questions?
In Assertion-Reason type of question, two statements are given, first is Assertion and second is called Reason. Student must have to think critically about both the statements in Assertion Reason Questions, since it combines multiple choice questions and true/false type of questions which requires a higher level of understanding.

How many types are there of Assertion Reason Type Questions?
Assertion-Reason type of questions can be asked either with four MCQ options or with five MCQ options. First four options are same in both the cases only one more options is being provided i.e. last one. One extra option increases the difficulty level of the questions.

In assertion reason type of questions, all 4 or 5 options are same for each question, which are as:

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
(e) Both Assertion and Reason are false.

Then a question haunts in every student’s mind, which option is correct and when?
This can be understood clearly with the following table:

Assertion (A)Reason (R)MCQ Options (Fixed for all questions)
If TrueTrue(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
If TrueTrue(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
If TrueFalse(c) Assertion (A) is true but reason (R) is false.
If FalseTrue(d) Assertion (A) is false but reason (R) is true.
If FalseFalse(e) Both Assertion and Reason are false.

Now, lets practice some Assertion Reason Questions of Physics: Chapter 4 Moving Charges and Magnetism

For question given below, two statements are given- one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

(a) Both A and R are true and R is correct explanation of the assertion.
(b) Both A and R are true but R is not the correct explanation of the assertion.
(c) A is true but R is false.
(d) A is false but R is true.

Question.1.
Assertion: Cyclotron is a device which is used to accelerate the positive ion.
Reason: Cyclotron frequency depends upon the velocity.

Ans.1. (c)
A is true but R is false.

Question.2.
Assertion: Cyclotron does not accelerate electron.
Reason: Mass of the electrons is very small.

Ans.2. (c)
A is true but R is false.

Question.3.
Assertion: In electric circuits, wires carrying currents in opposite directions are often twisted together
Reason: If the wires are not twisted together, the combination of the wires forms a current loop, the magnetic field generated by the loop might affect adjacent circuits
or components.

Ans.3. (a)
Both A and R are true and R is correct explanation of the assertion.

Question.4.
Assertion: The magnetic field produced by a current carrying solenoid is independent of its length and cross-sectional area.
Reason: The magnetic field inside the solenoid is uniform.

Ans.4. (b)
Both A and R are true but R is not the correct explanation of the assertion.

Question.5.
Assertion: A charge, whether stationary or in motion produces a magnetic field around it.
Reason: Moving charges produce only electric field in the surrounding space.

Ans.5. (d)
A is false but R is true.

Question.6.
Assertion: A proton and an alpha particle having the same kinetic energy are moving in circular paths in a uniform magnetic field. The radii of their circular paths will be equal.
Reason: Any two charged particles having equal kinetic energies and entering a region of uniform magnetic field B in a direction perpendicular to B, will describe circular trajectories of equal radii.

Ans.6. (c)
A is true but R is false.

Question.7.
Assertion: If the current in a solenoid is reversed in direction while keeping the same magnitude, the magnetic field energy stored in the solenoid remains unchanged.
Reason: Magnetic field energy density is proportional to the magnetic field.

Ans.7. (c)
A is true but R is false.

Question.8.
Assertion: The magnetic field at the centre of the circular coil in the following figure due to the currents I_{1} and I_{2} is zero.
Reason: I_{1} = I_{1} implies that the fields due to the current I_{1} and I_{2} will be balanced.

Ans.8. (d)
A is false but R is true.

Question.9.
Assertion: If the current in a solenoid is reversed in direction while keeping the same magnitude, the magnetic field energy stored in the solenoid decreases.
Reason: Magnetic field energy density is proportional to square of current.

Ans.9. (d)
A is false but R is true.

Question.10.
Assertion: Free electrons always keep on moving in a conductor even then no magnetic force act on them in magnetic field unless a current is passed through it.
Reason: The average velocity of free electron is zero.

Ans.10. (b)
Both A and R are true but R is not the correct explanation of the assertion.

Question.11.
Assertion: To convert a galvanometer into an ammeter a small resistance is connected in parallel with it.
Reason: The small resistance increases the combined resistance of the combination.

Ans.11. (c)
A is true but R is false.