CBSE Class 12 · 2014 · Delhi · Magnetic Effects of CurrentVery Short Answer

Using the concept of force between two infinitely long parallel current-carrying conductors, define one ampere of current.

Solution

Two parallel wires a distance

r

apart carrying currents

I_{1}, I_{2}

exert a force per unit length

\frac{F}{ℓ} = \frac{μ _{0} I _{1} I _{2}}{2 π r}

. Setting

I_{1} = I_{2} = 1 A

and

r = 1 m

gives

\frac{F}{ℓ} = \frac{( 4 π \times 1 0 ^{- 7} ) ( 1 ) ( 1 )}{2 π ( 1 )} = 2 \times 1 0^{- 7} N/m

, which is the SI definition of the ampere.

CBSE Class 12 Board · 2014 · Delhi · Subjective