Question

Previous year Jee mains question

chapter :- magnetic effect of current . ​

Answer 1

Answer:

Option (c) 1

Explanation:

Given :- radius "a"

current "I"

We have to find the ratio of the magnetic field at a/2 and 2a

Charge density , J = I /πa²

From Ampere's law circuital law,

→ ∮B•dl = μ₀ • I (enclosed)

for r <a

• B × 2 πr = μ₀ × J × πr²

• → B = μ₀ I / πr² × r/2

• At r = a/2 , B₁ = μ₀I /4πa

Similarly

For, r > a ,

• → B×2πr = μ₀I

• → B = μ₀ I / 2πr

• At r = 2a ,

• → B₂ = μ₀ I / 4πa

• B₁/B₂ = 1 Answer