Question

A solenoid of length $20cm$ and radius $2cm$ is closely wound with $200$ turns. The magnetic field intensity at either end of the solenoid when the current in the winding is $5amp.$ is

• A. $2500Amp/m$
• B. $2000Amp/m$
• C. $1750Amp/m$
• D. $2940Amp/m$

Answer 1

The correct option is A $2500Amp/m$

Given: length=20 cm, r=2 cm ,N=200 ,i=5 amp

Solution: We know the formula of solenoid at the end of solenoid is half as that of the center.

$B_{end}=\frac{B_{centre}}{2}=\frac{{\mu }_{0}ni}{2}$

Magnetic field intensity( H)$=\frac{B}{{\mu }_0}$

$H=\frac{B\times {\mu }_{0}ni}{2{\mu }_0}$

After putting values ,we get:

H=2500A/m

Hence the correct option is A