Magnetic force, magnetic field of circular coils, and intersecting field lines

Question 1

A vertical wire is carrying a current in the upward direction. It is placed in a magnetic field, pointing towards the East direction. Find out the direction of force on the wire.

Accepted Answer

Using Fleming's Left-Hand Rule: - Forefinger (magnetic field) points East. - Middle finger (current) points Upwards. - Thumb (force) points **into the page / Towards North?** Let's check: East is right, Upwards is up $\rightarrow$ Thumb points Into the page (or West/South depending on coordinates). In standard 2D cardinal plane: Current = Up (North), Magnetic Field = East $\Rightarrow$ Force = Into the page.

Question 2

Out of the two current carrying circular coils, coil 'A' has 10 turns while coil B has 15 turns. Which of the two coils will produce a stronger magnetic field at its centre if same current is flowing through both the coils? Explain with reason.

Accepted Answer

Coil **'B'** will produce a stronger magnetic field. Reason: Magnetic field produced by a circular coil is directly proportional to the number of turns ($B \propto N$). Since Coil B has more turns ($15 > 10$), field strength at its center is greater.

Question 3

In the given figure, AB and CD are two magnetic field lines intersecting each other at point O. If a compass is placed at point O, what will happen? State your conclusions.

Accepted Answer

The compass needle will get confused/oscillate and cannot point in two directions at the same time. Conclusion: Two magnetic field lines can **never intersect** each other because if they did, the magnetic field at the point of intersection would have two different directions, which is impossible.

Magnetic force, magnetic field of circular coils, and intersecting field lines

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