Suppose you left a 100-W light bulb on continuously for one month. If the electricity generation and transmission efficiency is 30%, how much chemical energy (in joules) was wasted at the power plant for this oversight? If the fuel consumption for one meal in Cambodia using a kerosene wick stove is 6 MJ (1 MJ = 1,000,000 joules), how many equivalent meals could be cooked with this wasted energy.

Respuesta :

Answer:

a

 [tex]E_g  =  240 \  kWh [/tex]

b

[tex]N = 144 \ meals [/tex]

Explanation:

From the question we are told that

The power rating of the bulb is P = 100 W

The duration is t = 1 month = 1 * 30 * 24 = 720 h

The efficiency is [tex]\eta = 30\% = 0.30[/tex]

The fuel consumption for one meal is [tex]E = 6 MJ = 6 *10^6 J[/tex]

Generally the energy consumed by the bulb is mathematically represented as

[tex]E_c = P * t[/tex]

=> [tex]E_c = 100 * 720 [/tex]

=> [tex]E_c = 72\ k Wh [/tex]

Generally the energy generated at the power plant that was wasted by the bulb is mathematically represented as

[tex]E_g = \frac{E_c}{\eta}[/tex]

=> [tex]E_g = \frac{72000}{0.3}[/tex]

=> [tex]E_g = 240 \ kWh [/tex]

Converting this value  to  Joules

       [tex]E_g  =  240  *   3.6 * 10^{6}  =  8.64*10^8  [/tex]

Generally the number of means that would be cooked is

[tex]N = \frac{8.64*10^8 }{6 *10^6}[/tex]

=>    [tex]N =  144 \  meals [/tex]

The wasted chemical energy be "8.64 × 10⁸ J" and the equivalent meals could be cooked be "144".

Chemical energy

According to the question,

Bulb power, P = 100 W

Time, t = 1 month or,

            = 1 × 30 × 24

            = 720 h

Efficiency, η = 30% or,

                     = 0.30

Fuel consumption, E = 6 MJ or,

                                   = 6 × 10⁶ J  

Energy consumed be:

→ [tex]E_c[/tex] = P × t

By substituting the values,

       = 100 × 720

       = 72 kWh

Wasted energy be:

→ [tex]E_g[/tex] = [tex]\frac{E_c}{\eta}[/tex]

       = [tex]\frac{72000}{0.3}[/tex]

       = 240 kWh or,

       = 240 × 3.6 × 10⁶

       = 8.64 × 10⁸ J

and,

The no. of meals be:

→ N = [tex]\frac{8.64\times 10^8}{6\times 10^6}[/tex]

      = 144 meals

Thus the answers above are correct.      

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