Class 12 Physics
CBSE and UP Board
Moving Charges and Magnetism
Chapter-4 Exercise 4.2
NCERT Solutions Class 12 Physics Chapter 4 Question 2
A long straight wire carries a current of 35 A. What is the magnitude of the field B at a point 20 cm from the wire?
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Current in the wire, I = 35 A
Distance of a point from the wire, r = 20 cm = 0.2 m
Magnitude of the magnetic field at this point is given as:
|B|= (μ0/4π) 2l/r
Where, μ0 = Permeability of free space = 4π x 10-7 T m A-1
|B|= (4π x 10-7 )/4π x ( 2 x 35 )/0.2 = 3.5 x 10⁻⁵ T
Hence, the magnitude of the magnetic field at a point 20 cm from the wire is 3.5 x 10–5 T.