Question

A solenoid is defined as a long helical coil of insulated wire with many closely spaced turns. Which geometric condition must it satisfy to be classified as a 'long' solenoid?

विकल्प

• Its length \(l\) must be exactly equal to its radius \(R\), i.e., \(l = R\)

• Its radius \(R\) must be much greater than its length \(l\), i.e., \(R \gg l\)

• Its length \(l\) must be much greater than its radius \(R\), i.e., \(l \gg R\)

• Its length \(l\) must be much less than its radius \(R\), i.e., \(l \ll R\)

Answer 1

A solenoid qualifies as a 'long' solenoid only when its length \(l\) is much greater than its radius \(R\) (\(l \gg R\)). This condition ensures a strong, uniform magnetic field inside and a negligible field outside. If this condition is not met, the standard formula \(B = \mu_0 n I\) does not accurately apply.