What does a wattmeter indicate?

• A. Power
• B. Power factor
• C. Voltage
• D. Current

Answer: (B)

A wattmeter measures real power, the rate at which energy is actually transferred to the load. In AC circuits the meter’s mechanism responds to the average product of voltage and current, which equals P = VI cos φ, where φ is the phase angle between voltage and current. That means the reading is in watts and reflects the usable power delivered. Voltage and current are read by separate meters, and power factor—cos φ—is a separate concept that relates real power to apparent power (S = VI). So the wattmeter’s role is to indicate real power, not power factor, voltage, or current.