One single phase wattmeter operating on 230 V and 5 A for 5 hours make...
Given that,
Voltage (V) = 230 V
Current (I) = 5 A
Time (t) = 5 hours

Number of revolutions = 1940
Meter constant = 400
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One single phase wattmeter operating on 230 V and 5 A for 5 hours make...
Given:
- Single phase wattmeter operating on 230 V and 5 A
- It makes 1940 revolutions in 5 hours
- Meter constant in revolution is 400
To Find:
- The power factor of the load
Explanation:
The power consumed by the load can be calculated using the formula:
Power (P) = Voltage (V) x Current (I) x Power Factor (PF)
The meter constant in revolution is given as 400, which means that for every 400 revolutions of the wattmeter, one unit of electrical energy is consumed by the load.
Step 1: Calculate the total energy consumed by the load
The total energy consumed by the load can be calculated using the formula:
Total Energy (E) = Number of Revolutions x Meter Constant in Revolution
For the given problem, the number of revolutions is 1940 and the meter constant is 400. Therefore,
Total Energy (E) = 1940 x 400 = 776000 units
Step 2: Calculate the power consumed by the load
The power consumed by the load can be calculated using the formula:
Power (P) = Total Energy (E) / Time (t)
For the given problem, the time is 5 hours. Therefore,
Power (P) = 776000 / 5 = 155200 units per hour
Step 3: Calculate the power factor
The power factor can be calculated using the formula:
Power Factor (PF) = Power (P) / (Voltage (V) x Current (I))
For the given problem, the voltage is 230 V and the current is 5 A. Therefore,
Power Factor (PF) = 155200 / (230 x 5) = 0.676
Since the power factor is generally expressed as a decimal, the power factor is approximately 0.676.
Conclusion:
The power factor of the load is approximately 0.676, which is closest to option B (0.8).