Question 1

What is the magnetic field at the centre of a current-carrying circular loop?

Accepted Answer

At the centre of a circular loop of radius R carrying current I, B = μ₀I / 2R. The direction follows the right-hand rule: curl your fingers along the current and your thumb points along B. Doubling the radius halves the field if the current stays the same.

Question 2

Why is the magnetic field inside a solenoid uniform?

Accepted Answer

When identical current loops are stacked closely together, their fields add along the common axis while the transverse (stray) components cancel between neighbouring turns. Deep inside a long solenoid every interior point sees the same contribution from turns ahead and behind, so the field lines become straight, parallel and equally spaced — a uniform field of magnitude B = μ₀nI.

Question 3

Why is the field at the end of a solenoid half the interior value?

Accepted Answer

For an ideal LONG solenoid, symmetry arguments applied to the two ends of an Amperian pillbox give B_end = μ₀nI / 2. It is a limiting result valid only when the length greatly exceeds the radius; a short or finite coil has an end field slightly different from exactly half, because end turns contribute asymmetrically.

Question 4

What is the right-hand thumb rule for a current loop?

Accepted Answer

Curl the fingers of your right hand in the direction of the current flowing around the loop; your extended thumb points in the direction of the magnetic field through the loop's centre. Reversing the current reverses the field and swaps the north and south faces of the loop.

Question 5

How does the number of turns per unit length affect the field inside a solenoid?

Accepted Answer

The interior field is directly proportional to n = N/L, the turns per unit length: B = μ₀nI. Packing more turns into the same length (or adding turns while keeping the length fixed) increases B linearly. Note it is turns PER METRE that matters, not the raw turn count.

Magnetic Field Lines: Ek Loop se Solenoid Tak

Practice

Learned it? Now prove it under the clock.