Physics · Moving Charges And Magnetism · NEET
No. In Oersted's experiment the compass needle stays still when the switch is off. The needle deflects only while current flows. So the magnetic field is produced by moving charges (the current), not by the wire itself. Switch off the current and the field disappears.
The needle turns so it lines up along the circular field lines around the wire. If you reverse the current direction, the needle deflects the opposite way. This reversal is the key proof that current direction sets the field direction. Use the right-hand thumb rule: thumb points along current, curled fingers show the field (and needle) direction.
It is circular. The field lines are concentric circles around the wire, lying in a plane perpendicular to the wire. This is why iron filings around a current wire form rings, and why a compass needle placed at different points around the wire points in different tangential directions.
No. A charge at rest makes only an electric field. A magnetic field appears only when the charge moves, i.e. when there is a current. Oersted's result is exactly this: current (moving charge) is needed to deflect the needle. This is why the topic sits under 'Moving Charges and Magnetism'.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It proved that an electric current produces a magnetic field. A current in a straight wire deflected a nearby compass needle, giving the first evidence that electricity and magnetism are connected.
In 1820. NCERT notes this was about 200 years after electricity and magnetism were first studied separately, and it was Oersted who linked them.
It is the starting idea for the whole chapter Moving Charges and Magnetism. Every later formula (Biot-Savart law, field of a straight wire B = mu0 I / 2 pi r, Ampere's law) builds on the fact Oersted found: current makes a magnetic field.
The needle deflects in the opposite direction. Reversing the current reverses the magnetic field direction, which is predicted by the right-hand thumb rule.
Right-hand thumb rule: point the right thumb along the direction of conventional current, and the curled fingers show the circular direction of the magnetic field lines around the wire.
