JEE Main · 2024 · 04 Apr 2024 · Shift 1 · Electrostatics

An infinitely long positively charged straight thread has a linear charge density

λ Cm^{- 1}

. An electron revolves along a circular path having axis along the length of the wire. The graph that correctly represents the variation of the kinetic energy of electron as a function of radius of circular path from the wire is :

(A)(see structure)
(B)(see structure)
✓ Correct
(C)(see structure)
(D)(see structure)

Answer: (B)

Solution

The electron moves in a circle of radius

r

around the charged thread. The field of the line charge is

E = \frac{2 k λ}{r}

, so the electrostatic force provides the centripetal force:

\frac{m v ^{2}}{r} = e E = \frac{2 k λ e}{r} \Rightarrow m v^{2} = 2 k λ e .

Then

K E = \frac{1}{2} m v^{2} = k λ e = constant,

independent of

r

. The graph is a horizontal line

\Rightarrow

option B.

JEE Main · 2024 · 04 Apr 2024 · Shift 1 · Single correct option

Practise more: all JEE Main PYQs on Electrostatics →

JEE Main · 2024 · 04 Apr 2024 · Shift 1 · Electrostatics

Solution

More JEE Main questions on Electrostatics