One kilowatt hour of electrical energy is the same as

Question

Examoogle · Accepted Answer

$36 	imes 10^5$ joules

Explanation: One kilowatt-hour (kWh) is the commercial unit of electrical energy, representing the total work done by a power of 1 kilowatt sustained for 1 hour. It is derived from the base SI unit, the Joule, by converting power (kW to W) and time (hours to seconds).

Working Principle: The principle is based on the relationship $Energy (E) = Power (P) 	imes Time (t)$. Since $1 kW = 10^3 W$ and $1 hour = 3600 seconds$, we calculate $1 kWh = (10^3 W) 	imes (3600 s) = 3.6 	imes 10^6 J$, which is equivalent to $36 	imes 10^5 J$.

Key Formulas: $1 kWh = 1 kW 	imes 1 h$; $1 kWh = 10^3 W 	imes 3600 s = 3.6 	imes 10^6 J$

Key Points: 1 kWh is commonly known as 1 'unit' of electricity in domestic billing.; Joule is the SI unit of energy (1 Joule = 1 Watt-second).; Conversion factor: $1 kWh = 3.6 	imes 10^6 J$.

Advantages: Standardized global unit for electricity billing.; Easily measurable using energy meters (kilowatt-hour meters).

Disadvantages: Not a standard SI unit (Joule is the SI unit).; Can be confused with kW (power) by non-technical users.

Applications: Electricity utility billing.; Quantifying energy storage capacity of batteries.; Evaluating efficiency of electrical appliances.

Additional Info: Option A is incorrect because watts are units of power, not energy.. Option B is incorrect because ergs are the CGS unit of energy ($1 J = 10^7 ergs$).. Option D is incorrect because B.T.U. is a thermal energy unit ($1 kWh \approx 3412 BTU$).

Answer: C is correct — 1 kWh equals 3.6 million Joules, or $36 	imes 10^5$ Joules.

Exam Tip: Remember that energy is power integrated over time; always ensure time is in seconds when converting to Joules.

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