UNIT 2 Quiz

What is the principle of operation of an electrodynamic wattmeter?

• It uses the interaction between a magnetic field and a current-carrying conductor.

• It relies on the heating effect of current.

• It measures power based on electrostatic forces.

• It operates on the principle of electromagnetic induction between fixed and moving coils.

In an electrodynamic wattmeter, what do the current coil and voltage coil represent?

• Current coil is fixed, voltage coil is moving.

• Current coil carries the load current, voltage coil is connected across the supply.

• Both coils are fixed and measure resistance.

• Voltage coil carries the load current, current coil measures voltage.

What is a common error in electrodynamic wattmeters that can be minimized by using a compensating coil?

• Error due to temperature variations.

• Error due to mutual inductance between coils.

• Error from eddy currents.

• Error caused by friction in the moving system.

For power measurement in a single-phase circuit, how is the wattmeter connected?

• Current coil in parallel with the load, pressure coil in series.

• Current coil in series with the load, pressure coil in parallel with the load.

• Both coils in series with the load.

• Both coils in parallel with the load.

In a single-phase AC circuit, the power measured by a wattmeter is given by P = V * I * cosφ. What does cosφ represent?

• The phase angle between voltage and resistance.

• The power factor of the circuit.

• The ratio of reactive power to apparent power.

• The frequency of the supply.

What happens if the wattmeter is connected with reversed polarity in a single-phase DC circuit?

• It reads zero power.

• It shows a negative deflection, indicating reverse power flow.

• It measures reactive power instead.

• The instrument gets damaged.

In a balanced three-phase system, which method is commonly used for power measurement?

• One-wattmeter method.

• Two-wattmeter method.

• Four-wattmeter method.

• Single-phase wattmeter across all phases.

In the two-wattmeter method for a three-phase system, the total power is calculated as:

• Sum of the two wattmeter readings.

• Difference of the two wattmeter readings.

• Average of the two wattmeter readings.

• Product of the two wattmeter readings.

For an unbalanced three-phase load with a neutral wire, how many wattmeters are required to measure total power?

• One wattmeter.

• Two wattmeters.

• Three wattmeters.

• Four wattmeters.

In a three-phase system using the two-wattmeter method, if one wattmeter reads zero, what does it indicate?

• The power factor is unity.

• The power factor is 0.5.

• The load is purely resistive.

• There is no power consumption.