Interactive Assertion-Reason Questions: Electric Field and Charges Class XII | Electrostatics

Question 1

Assertion (A): When we rub a glass rod with silk, the rod gets positively charged and the silk gets negatively charged.
Reason (R): On rubbing, electrons from the silk cloth move to the glass rod.

Select the correct choice:

• 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. Both Assertion (A) and Reason (R) are false.

Answer and Explanation

Answer: (c)
Explanation: When we rub a glass rod with silk, electrons are actually transferred from the glass rod to the silk. As a result, the glass rod becomes positively charged while the silk becomes negatively charged. Thus, the Assertion is true but the Reason is false.

Question 2

Assertion (A): A negative charge in an electric field moves along the direction of the electric field.
Reason (R): On a negative charge, a force acts in the direction of the electric field.

Select the correct choice:

• 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. Both Assertion (A) and Reason (R) are false.

Answer and Explanation

Answer: (d)
Explanation: A negative charge actually experiences a force in the direction opposite to that of the electric field; hence, it moves opposite to the electric field. Therefore, both the Assertion and Reason are false.

Question 3

Assertion (A): If there exists Coulomb attraction between two bodies, both of them may not be charged.
Reason (R): In Coulomb attraction two bodies are oppositely charged.

Select the correct choice:

• 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. Both Assertion (A) and Reason (R) are false.

Answer and Explanation

Answer: (b)
Explanation: Coulomb attraction exists between two bodies when one is charged and the other is uncharged as well as between two oppositely charged bodies. Therefore, while the Reason (which implies the bodies are necessarily oppositely charged) is true, it is not the correct explanation for the Assertion. Hence, both are true but the Reason is not the correct explanation.

Question 4

Assertion (A): The force with which two charges attract or repel each other is not affected by the presence of a third charge.
Reason (R): The force on any charge due to a number of other charges is the vector sum of all the forces on that charge due to the other charges, taken one at a time.

Select the correct choice:

• 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. Both Assertion (A) and Reason (R) are false.

Answer and Explanation

Answer: (b)
Explanation: In accordance with the principle of superposition, the force on any charge is the vector sum of the forces due to each of the other charges taken separately. Although the presence of other charges does not affect the individual force between any two charges, the overall net force on a charge will be the sum of those individual forces. Thus, both the Assertion and Reason are true; however, the Reason is only explaining the method (superposition) and not directly why the force between two specific charges is unaffected by a third charge.