# Class 12 Physics Moving Charges and Magnetism: NCERT Solutions for Question 22

This page focuses on the detailed Moving Charges and Magnetism question answers for Class 12 Physics Moving Charges and Magnetism, addressing the question: 'The wires which connect the battery of an automobile to its starting motor carry a current of 300 A (for a short time). What is the force per unit length between the wires if they are 70 cm long and 1.5 cm apart? Is the force attractive or repulsive?'. The solution provides a thorough breakdown of the question, highlighting key concepts and approaches to arrive at the correct answer. This easy-to-understand explanation will help students develop better problem-solving skills, reinforcing their understanding of the chapter and aiding in exam preparation.
Question 22

## The wires which connect the battery of an automobile to its starting motor carry a current of 300 A (for a short time). What is the force per unit length between the wires if they are 70 cm long and 1.5 cm apart? Is the force attractive or repulsive?

Current in both wires, I = 300 A

Distance between the wires, r = 1.5 cm = 0.015 m

Length of the two wires, l = 70 cm = 0.7 m

Force between the two wires is given by the relation,

Where,

µ0 = Permeability of free space = 4π x 10-7TmA-1

Since the direction of the current in the wires is opposite, a repulsive force exists between them.