Question

The resistance of a moving coil voltmeter is 12000 ohm. The moving coil has 100 turns and is 4cm long and 3cm wide. The flux density in the air gap is 6¹⁰⁻² wb/m². Find the deflection produced by 300 V if the spring control gives a deflection of one degree for a torque of 25¹⁰⁻⁷ Nm and the spring constant is 25¹⁰⁻⁷ Nm/deg?

Answer 1

To calculate the moving coil voltmeter's deflection produced by 300 V, the current through the meter is first found using Ohm's law, and the torque balance with the spring control is then used to determine the deflection angle.

Step-by-step explanation:

The student is asking how to calculate the deflection produced by a 300 V potential difference across a moving coil voltmeter with given parameters including resistance, dimensions of the coil, flux density, spring control data, and spring constant.

To find the deflection, we must first calculate the current passing through the meter using Ohm's law, which is I = V/R, where V is the voltage and R is the resistance of the voltmeter. Knowing the current, we can then calculate the torque produced in the coil due to the magnetic interaction.

The deflection can be determined by considering the balance between magnetic torque and the spring torque, which is the product of the spring constant and the angle of deflection. Since 1 degree of deflection corresponds to a torque of 25×10⁻⁷ Nm, the relation between the torque produced by current in the magnetic field and the spring control allows us to find the required deflection angle.