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4 years ago

14

A 25-W compact fluorescent lightbulb (CFL) produces the light equivalent of a 100-W incandescent bulb. The population of North A

merica is estimated to be about 305 million. Estimate the amount of coal needed to light one 100-W incandescent lightbulb for each person for one year and the amount of coal that would be saved if each incandescent bulb were replaced with a CFL. Assume the coal has a NHV of 28.5 MJ · kg−1 and the power plants are 33% efficient.

1 answer:

wariber [46]4 years ago

8 0

Answer:

Coal required is 101 Teragram/year.

Coal saved is 25.25 Teragram/year.

Explanation:

1 Teragram is exactly 1000000000 kilograms.

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g A food department is kept at -12oC by a refrigerator in an environment at 30oC. The total heat gain to the food department is

boyakko [2]

Answer:

a) $\dot W = 0.417\,kW$ , b) $COP_{R} = 2.198$ , c) Irreversible.

Explanation:

a) The power input required by the refrigerator is:

$\dot W = \dot Q_{H} - \dot Q_{L}$

$\dot W = \left(4800\,\frac{kJ}{h} - 3300\,\frac{kJ}{h}\right)\cdot \left(\frac{1}{3600} \,\frac{h}{s} \right)$

$\dot W = 0.417\,kW$

b) The Coefficient of Performance of the refrigerator is:

$COP_{R} = \frac{\dot Q_{L}}{\dot W}$

$COP_{R} = \frac{3300\,\frac{kJ}{h} }{(0.417\,kW)\cdot \left(3600\,\frac{s}{h} \right)}$

$COP_{R} = 2.198$

c) The maximum ideal Coefficient of Performance of the refrigeration is given by the inverse Carnot's Cycle:

$COP_{R,ideal} = \frac{T_{L}}{T_{H}-T_{L}}$

$COP_{R,ideal} = \frac{261.15\,K}{303.15\,K - 261.15\,K}$

$COP_{R,ideal} = 6.218$

The refrigeration cycle is irreversible, as $COP_{R} < COP_{R,ideal}$ .

3 0

3 years ago

The equilibrium fraction of lattice sites that are vacant in electrum (a silver gold alloy) at 300K C is 9.93 x 10-8. There are

IrinaK [193]

Answer:

the density of the electrum is 14.30 g/cm³

Explanation:

Given that:

The equilibrium fraction of lattice sites that are vacant in electrum = $9.93*10^{-8}$

Number of vacant atoms = $5.854 * 10^{15} \ vacancies/cm^3$

the atomic mass of the electrum = 146.08 g/mol

Avogadro's number = $6.022*10^{23$

The Number of vacant atoms = Fraction of lattice sites × Total number of sites(N)

$5.854*10^{15}$ = $9.93*10^{-8}$ × Total number of sites(N)

Total number of sites (N) = $\dfrac{5.854*10^{15}}{9.93*10^{-8}}$

Total number of sites (N) = $5.895*10^{22}$

From the expression of the total number of sites; we can determine the density of the electrum;

$N = \dfrac{N_A \rho _{electrum}}{A_{electrum}}$

where ;

$N_A$ = Avogadro's Number

$\rho_{electrum} =$ density of the electrum

$A_{electrum}$ = Atomic mass

$5.895*10^{22} = \dfrac{6.022*10^{23}* \rho _{electrum}}{146.08}$

$5.895*10^{22} *146.08}= 6.022*10^{23}* \rho _{electrum}$

$8.611416*10^{24}= 6.022*10^{23}* \rho _{electrum}$

$\rho _{electrum}=\dfrac{8.611416*10^{24}}{6.022*10^{23}}}$

$\mathbf{ \rho _{electrum}=14.30 \ g/cm^3}$

Thus; the density of the electrum is 14.30 g/cm³

7 0

3 years ago

Who invented engineering first?

astra-53 [7]

Explanation:

The earliest civil engineer known by name is Imhotep. As one of the officials of the Pharaoh, Djosèr, he probably designed and supervised the construction of the Pyramid of Djoser (the Step Pyramid) at Saqqara in Egypt around 2630–2611 BC.

8 0

3 years ago

The barrel of a bicycle tire pump becomes quite warm during use. Explain the mechanisms responsible for the temperature increase

Alexeev081 [22]

Answer:

The air heats up when being compressed and transefers heat to the barrel.

Explanation:

When a gas is compressed it raises in temperature. Assuming that the compression happens fast and is done before a significant amount of heat can be transferred to the barrel, we could say it is an adiabatic compression. This isn't exactly true, it is an approximation.

In an adiabatic transformation:

$P^{1-k} * T^k = constant$

For air k = 1.4

SO

$P0^{-0.4} * T0^{1.4} = P1^{-0.4} * T1^{1.4}$

$T1^{1.4} = \frac{P1^{0.4} * T0^{1.4}}{P0^{0.4}}$

$T1^{1.4} = \frac{P1}{P0}^{0.4} * T0^{1.4}$

$T1 = T0 * \frac{P1}{P0}^{0.4/1.4}$

$T1 = T0 * \frac{P1}{P0}^{0.28}$

SInce it is compressing, the fraction P1/P0 will always be greater than one, and raised to a positive fraction it will always yield a number greater than one, so the final temperature will be greater than the initial temperature.

After it was compressed the hot air will exchange heat with the barrel heating it up.

5 0

3 years ago

Which statement explains what causes the balloon to accelerate

victus00 [196]

The air leaving through the balloon's mouth pulls the balloon in the same direction as the exiting air, so the balloon experiences a net force. All air surrounding the balloon pushes the balloon forward.

5 0

3 years ago