Question

Solenoid of radius r & length l is shown in figure, current i is passed through it. Then,

• A. r =l is necessary for $B={\mu }_{0}ni$
• B. l >> r is necessary for $B={\mu }_{0}ni$
• C. We can apply $B={\mu }_{0}ni$ even if winding is not tight.
• D. r >> l is necessary for $B={\mu }_{0}ni$

Answer 1

The correct option is B l >> r is necessary for $B={\mu }_{0}ni$

A solenoid must obey two conditions for it to be an ideal solenoid :
1. length of the solenoid >> radius of the solenoid.
2. The winding should be perfectly tight.
For an ideal solenoid, $B={\mu }_{0}ni$