Energy Production (topic 8)

Question 1

Sankey Diagrams

Answer 1

Width of the arrows = power or energy

Question 2

Effinciency equation

Answer 2

Efficiency = useful output / total input

Question 3

Energy density equation

Answer 3

Energy density = energy released / mass of fuel used

Question 4

How to generate electricity

Answer 4

1. Energy source
   
   • steam (heat)
   • fossil fuel (heat)
   • nuclear (heat)
   • wind (Ek)
   • wave (Ek)
   • hydroelectric (Ek)
2. Turn a turbine with magnets. Electromagnetism.
3. Generate electricity

Question 5

Nuclear energy

Answer 5

1. Nuclear energy (start with U235 uranium)
2. Thermal energy (add a neutron and chain reaction starts)
3. Kinetic energy
4. Turbine

Fuel rods expel neutrons to other fuel rods which causes a chain reaction. There are control rods in between each fuel rods to absorb neutrons and control the reaction.

**Control rods absorb neutrons. Usually made of carbon or an element that can absorb neutrons.

Question 6

Power equation that works for any case

Answer 6

Power (P) = energy / time

power = W or J sec^-1
energy = J
time = sec

Question 7

Power equation for wind energy

Answer 7

Power = (1 / 2) A p v^3

where
Power = W or J sec^-1
A = cross sectional area of air (m^2) (pi r^2)
p (ro) = density of air (kg m^-3)
v = speed of air (m s^-1)

Question 8

Power equation for solar energy

Answer 8

I = power / area

where
I = intensity of radiation (apparent brightness) (W m^-2)
power = luminosity of the star (W or J sec^-1)
area = surface area of a sphere (m^2) (4 pi r^2)

Question 9

Wien’s displacement law

Answer 9

lambda max = (2.9 x 10^-3) / T (kelvin)

where
lambda max = wavelength that gives peak intensity
T = temperature of a blackbody with similar temperature

Question 10

Blackbodies

Answer 10

A perfect absorber / emitter of radiation

Question 11

Peak wavelengths

Answer 11

Hotter wavelengths have higher peaks and are more toward the left of the graph while cooler wavelengths have lower peaks and are more toward the right of the graph.

I vs lambda or intensity vs wavelength graphs

Question 12

Stefan-Boltzmann law

Answer 12

P = eσAT^4

where
P = power (W or J sec^-1)
e = emmisivity (=1 unless otherwise told)
σ = Stefan-Boltzmann constant
A = surface area of a sphere = 4 pi r^2 (m^2)
T = surface temperature (K)

Question 13

Albedo equation

Answer 13

Albedo = total scattered power / total incident power = I(out) / I(in)

**high albedo (1) -> very bright, reflects lots

Question 14

Total incident energy

Answer 14

Total incident energy = energy intensity x area x time

Question 15

Electrical energy obtained

Answer 15

Electrical energy obtained = total energy x efficiency