Question

Which of the following is / are the units of strength of magnetic field at a point?

• A. $NA{m}^{-1}$
• B. NA m
• C. $N{A}^{-1}{m}^{-1}$
• D. $N{A}^{-2}{m}^{-2}$

Answer 1

The correct option is C $N{A}^{-1}{m}^{-1}$

SI unit of B is tesla (T) or weber / metre${}^2$, ie, $\left(wb/m^2\right)$
As, $B=\frac{F}{qvsin\theta }$
If $q=1C,v=1/m,\theta ={90}^o$
as $sin\theta =1$
and $F=1N$
then, $B=\frac{1}{1\times 1\times 1}=1T$
Thus, the magnetic field induction at a point is said to be a tesla, if a charge of 1 coulomb while moving at right angle to a magnetic field, with a velocity of1 m/s experiences a force of 1 N at that point.
Hence, $1T=\frac{1N}{1C\times 1m{s}^{-1}}$
$=\frac{1N}{1As\times 1m{s}^{-1}}$ $(1C=1ampere\times 1second)$