JEE Main & Advanced Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव Solenoid

A cylinderical coil of many tightly wound turns of insulated wire with generally diameter of the coil smaller than its length is called a solenoid.

A magnetic field is produced around and within the solenoid. The magnetic field within the solenoid is uniform and parallel to the axis of solenoid.

(1) Finite length solenoid : If \[N=\] total number of turns, \[l=\] length of the solenoid, \[n=\] number of turns per unit length \[=\frac{N}{l}\]

(i) Magnetic field inside the solenoid at point P is given by  \[B=\frac{{{\mu }_{0}}}{4\pi }(2\pi \,ni)[\sin \alpha +\sin \beta ]\]

(ii) Infinite length solenoid : If the solenoid is of infinite length and the point is well inside the solenoid i.e. \[\alpha =\beta =(\pi /2)\].

So           \[{{B}_{in}}={{\mu }_{0}}ni\]

(iii) If the solenoid is of infinite length and the point is near one end i.e. \[\alpha =0\] and \[\beta =(\pi /2)\] so \[{{B}_{end}}=\frac{1}{2}\mathbf{(}{{\mu }_{\mathbf{0}}}ni\mathbf{)}\]       (\[{{B}_{end}}=\frac{1}{2}{{B}_{in}}\])