The commercial unit of electrical energy, on which a household bill is calculated, is the
- A.watt
- B.volt ampere
- C.kilowatt hour
- D.joule per second
Correct answer
Explanation
The correct answer is C, the kilowatt hour. It is the energy consumed by an appliance of one kilowatt working for one hour, and it equals three point six million joules. The electricity meter in a house counts these units, which is why the kilowatt hour is often called simply a unit of electricity.
Option A, the watt, is the SI unit of power, that is the rate of using energy, not of energy itself, so it cannot appear on a bill as a quantity consumed. Option B, the volt ampere, is also a unit of power, used for apparent power in alternating current work, and again measures a rate. Option D, the joule per second, is just another name for the watt and so has the same problem. Only the kilowatt hour multiplies power by time and therefore measures energy.
Read the full article: Electricity and Magnetism: Laws, Rules and PYQs
Practice Questions
View allIf the potential difference across the ends of a conductor is halved, what happens to the current flowing through it?
- A.It gets increased
- B.It gets doubled
- C.It gets decreased
- D.It gets halved
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By Ohm's law, at a constant temperature the current through a conductor is directly proportional to the potential difference across its ends, since the current equals the potential difference divided by the resistance.
Read the full explanation →What is the work done to move a unit charge from one point to another in an electric circuit carrying some current, between those two points?
- A.Pressure distance
- B.Potential difference
- C.Potential distance
- D.Pressure difference
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The potential difference between two points in a circuit is defined as the work done in moving a unit positive charge from one point to the other.
Read the full explanation →Which of the following is NOT based on the heating effect of current?
- A.Electric heater
- B.Electric bulb (with filament)
- C.Electric iron
- D.Microwave
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A microwave oven does not cook by passing a current through a resistance. It generates microwaves in a magnetron, and these waves make the water molecules in the food rotate rapidly, so the food heats from within by dielectric heating.
Read the full explanation →A 12 V battery is connected across an unknown resistor. If a current of 2 mA is flowing through the circuit, the value of the resistance is _________ .
- A.600 ohm
- B.6 ohm
- C.6000 ohm
- D.60 ohm
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By Ohm's law the resistance equals the potential difference divided by the current. Here the current must first be converted into the base unit: two milliampere is 0.002 ampere.
Read the full explanation →Thin wires of which of the following metal is used for making the filament of electric bulbs?
- A.Tungsten
- B.Silver
- C.Nichrome
- D.Copper
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Tungsten has the highest melting point of all metals, well above three thousand degrees Celsius, so a thin tungsten wire can be heated until it glows white without melting.
Read the full explanation →