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NCERT Class XII Chapter
Moving Charges and Magnetism
Questions With Solutions

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Question : 22
Total: 28
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?
Solution:  
Two wires connecting battery of an automobile to the starting motor carry 300 A current in opposite direction. So, the force is repulsive between them.
Force per unit length
F/l =
µ0
4π
2I1I2
r
 = 10−7 ×
2×300×300
1.5×10−2
 = 1.2 N m−1
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