The magnetic field around a current-carrying wire

When a current flows in a wire, it creates a circular magnetic field around the wire. This magnetic field can deflect the needle of a magnetic compass. The strength of the magnetic field is greater closer to the wire, and increases if the current increases.

Wire runs vertically, current flowing bottom to top. Magnetic field rotates anticlockwise. Second wire runs vertically, current flowing top to bottom. Magnetic field rotates in a clockwise direction.Magnetic fields around a wire carrying an electric current

The direction of the current and magnetic field can be found using the right hand grip rule. Coil the fingers of the right hand as if holding the handlebars of a bicycle, with the thumb pointing away from the hand. The thumb indicates the direction of the current, and the fingers then indicate the direction of the magnetic field.

Solenoids

A solenoid consists of a wire coiled up into a spiral shape. When an electric current flows, the solenoid acts as an electromagnet. The shape of the magnetic field is very similar to the field of a bar magnet.

The field inside a solenoid is strong and uniform. The small magnetic fields caused by the current in each coil add together to make a stronger overall magnetic field. Outside the solenoid, the small magnetic fields from each wire cancel each other out and the outside field is much weaker.

Current flows towards you in the top five wires, away from you in bottom five. Magnetic fields flow anti-clockwise around top five wires, clockwise around bottom. North pole right. South pole left.A solenoid, shown here in cross section, has a stronger electromagnetic field than a single straight wire

Electromagnets are used in devices such as door locks that can be controlled remotely and electric bells.

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