Magnetic effect of a current

The magnetic field forms concentric circles around the wire. The field is strongest closest to the wire and weakens with distance. The direction of the magnetic field can be determined using the right-hand grip rule: point your thumb in the direction of the current, and your fingers curl in the direction of the magnetic field.

Inside the solenoid, the magnetic field is strong and uniform, running parallel to the axis of the solenoid. Outside the solenoid, the magnetic field is similar to that of a bar magnet, with field lines emerging from one end and entering the other, completing loops. The field is much weaker outside than inside.

1. Pass a straight wire vertically through a piece of cardboard.
2. Pass a current through the wire using a power supply.
3. Sprinkle iron filings onto the cardboard around the wire.
4. Gently tap the cardboard.
5. The iron filings will align themselves along the magnetic field lines.
6. The pattern will be circular concentric rings around the wire.
7. Use a compass to determine the direction of the field at a point. The North pole of the compass will point in the direction of the magnetic field. Alternatively, use the right-hand grip rule to find the field direction.

1. As the current increases, the magnetic field strength increases. This means the magnetic field lines become more concentrated, especially inside the solenoid, and extend further from the solenoid's ends. The field pattern remains qualitatively the same (similar to a bar magnet).
2. You can determine the polarity (North and South poles) of the solenoid using the right-hand grip rule. If you grip the solenoid with your right hand, with your fingers pointing in the direction of the conventional current, then your thumb points towards the North pole of the solenoid.

1. A small current flows through the coil of the relay, creating a magnetic field.
2. This magnetic field attracts a pivoting armature/switch.
3. The movement of the armature closes (or opens) a separate circuit, allowing a larger current to flow through it.
Explanation: A small current in the coil activates a magnetic field strong enough to actuate a switch in a different circuit.

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The strength of the magnetic field decreases as the distance from the wire increases. The field strength is inversely proportional to the distance from the wire.

(a) Inside the solenoid, the magnetic field is relatively uniform and strong. (b) Outside the solenoid, the magnetic field is much weaker and non-uniform, decreasing rapidly with distance from the solenoid. It is similar to that of a bar magnet.

Increasing the current in a straight wire increases the strength of the magnetic field around the wire. The magnetic field lines become more concentrated, indicating a stronger field. The pattern remains circular around the wire, but the intensity of the field increases with higher current.

1. Increase the current flowing through the solenoid.
2. Increase the number of turns of wire in the solenoid.

Increasing either the current or the number of turns strengthens the electromagnet, increasing the density of the magnetic flux lines.