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The world consumes energy at the rate of about $466 EJ$ per year, where the joule$(J)$ is the SI energy unit.
Convert this figure to watts$(W)$ , where $W= 1 J/s$, and then estimate the average per capita energy consumption rate in watts.

I'm having trouble understanding this problem. Can someone please explain me in detail the way to solve this problem. First of all I do not know what the unit $EJ$ represents, is it $exajoule$?

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closed as off topic by Chris Eagle, Paul, Davide Giraudo, Norbert, Asaf Karagila Feb 2 '13 at 12:27

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2 Answers 2

up vote 1 down vote accepted

Seems that $\text{EJ}$ refers to exajoule, which is ${10}^{18}$ joules, according to Wikipedia...so we have

$$466 \;\text{EJ} = (466 \times {10}^{18}) \;\text{J/yr}$$ and this converts to $$\frac{(466 \times {10}^{18}) \;\text{J}} {1 \;\text{yr}} = \frac{(466 \times {10}^{18}) } {1 \times 365 \times 24 \times 60 \times 60}\; \text{W}$$ because 1 year has 365 days, 1 day has 24 hours, 1 hour has 60 minutes and 1 minute has 60 seconds. Do the division and you'll get ${1.47} \times {10}^{13} \;\text{W}$ for the world population.

The question asked for per-capita consumption. Hence, I'd assume the population is now 7 billion or $7 \times {10}^{9}$. So continuing the calculation, we have

$$\frac{{1.47} \times {10}^{13} \text{W}} {7 \times {10}^{9} \text{people} } = 2100 \text { W / person}$$

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All the rest is estimating the world population and dividing the result by that number. –  Andrea Orta Feb 2 '13 at 8:55

2100 w / person. If my neighbour eats two apples per day and i do not; that makes one apple per day each. Now we should kwow what the consumption is in the USA per-capita and then in Tanzania per-capita or in most of African countries where so many people do not still have electricity.

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