Single Choice

$$20{\text{ }}ampere$$ current is flowing in a long straight wire. The intensity of the magnetic field at a distance 10 cm from the wire will be

A$$4{\text{ x 1}}{{\text{0}}^{ - 5}}{\text{ }}Wb/{m^2}$$
Correct Answer
B$${\text{9 x 1}}{{\text{0}}^{ - 5}}{\text{ }}Wb/{m^2}$$
C$$8{\text{ x 1}}{{\text{0}}^{ - 5}}{\text{ }}Wb/{m^2}$$
D$$6{\text{ x 1}}{{\text{0}}^{ - 5}}{\text{ }}Wb/{m^2}$$

Solution

The magnetic field at a distance from the wire is:
$$B=\dfrac {\mu_0}{4\pi}.\dfrac {2i}{r}$$

$$=10^{-7}\times \dfrac {2\times 20}{10\times 10^{-2}}$$

$$=4\times 10^{-5}\ Wb/m^2$$

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