# A Tightly-wound, Long Solenoid Carries a Current of 2.00 A. an Electron is Found to Execute a Uniform Circular Motion Inside the Solenoid with a Frequency of 1.00 × 108 Rev S−1. - Physics

Short Note

A tightly-wound, long solenoid carries a current of 2.00 A. An electron is found to execute a uniform circular motion inside the solenoid with a frequency of 1.00 × 108 rev s−1. Find the number of turns per metre in the solenoid.

#### Solution

Given:
Magnitude of current in the solenoid, i = 2 A
Frequency of the electron, $f = 1 \times {10}^8$  rev/s

Mass of the electron, $\text{ m }= 9 . 1 \times {10}^{- 31}$  kg

Charge of the electron, $q = 1 . 6 \times {10}^{- 19} C$

We know that the magnetic field inside a solenoid is given by
B = µ0ni
If a particle executes uniform circular motion inside a magnetic field, the frequency of the particle is given by

$f = \frac{qB}{2\pi m}$
$\Rightarrow B = \frac{2\pi mf}{q}$
$\Rightarrow \mu_0 ni = \frac{2\pi mf}{q} [\text{ Using } (1)]$
$\Rightarrow n = \frac{2\pi mf}{\mu_0 qi}$
$= \frac{2\pi \times 9 . 1 \times {10}^{- 31} \times 1 \times {10}^8}{4\pi \times {10}^{- 7} \times 1 . 6 \times {10}^{- 19} \times 2}$
$= 1420$ turns/m

Concept: Solenoid and the Toroid - the Solenoid
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#### APPEARS IN

HC Verma Class 11, Class 12 Concepts of Physics Vol. 2
Chapter 13 Magnetic Field due to a Current
Q 58 | Page 253