MP Board · Class 10 · Science · Magnetic Effects of Electric CurrentExplain the principle, construction, and working of an electric generator (AC generator). Draw a neat labeled diagram for the same.

Principle of AC Generator\nAn electric generator works on the principle of electromagnetic induction, discovered by Michael Faraday. According to this principle, when a closed coil is rotated in a uniform magnetic field, an induced electric current is set up in the coil due to a continuous change in the magnetic flux linked with it. The mechanical energy supplied to rotate the coil is converted into electrical energy.

Construction\nAn AC generator mainly consists of the following essential components:

• Armature (Coil): A large rectangular coil $ABCD$ consisting of a large number of turns of insulated copper wire wound over a soft iron core. It is capable of rotating rapidly about a central axis inside the magnetic field.
• Field Magnets: A strong permanent magnet or an electromagnet with concave poles ($N$ and $S$) that provides a strong, uniform, and radial magnetic field across the armature coil.
• Slip Rings ($R_1$ and $R_2$): Two hollow metallic rings rigidly attached to the ends of the armature coil. These rings rotate along with the rotation of the coil.
• Carbon Brushes ($B_1$ and $B_2$): Two flexible stationary carbon pieces that press gently against the revolving slip rings. These brushes are used to collect the induced current from the slip rings and pass it onward to the external circuit load.

Working

• Let the armature coil $ABCD$ initially lie in a horizontal plane perpendicular to the magnetic field lines. When the coil is rotated clockwise by applying external mechanical force, side $AB$ moves downward while side $CD$ moves upward.
• Due to this motion across the magnetic field, magnetic flux linked with the coil changes continuously, inducing an electric current in the coil according to Fleming's Right-Hand Rule.
• Following this rule, the current flows along the path $ABCD$ in the first half-rotation. Consequently, brush $B_1$ acts as a positive terminal while $B_2$ acts as a negative terminal in the external circuit.
• After half a rotation (at $180^\circ$), the positions of arms $AB$ and $CD$ get interchanged. Now, arm $AB$ moves upward and $CD$ moves downward. The direction of the induced current reverses and flows along the path $DCBA$.
• Now, brush $B_2$ becomes positive and $B_1$ becomes negative. Because the direction of the induced current changes its polarity after every half rotation, the current generated is alternating current (AC).