Electricity Generation and Distribution/Solar Energy

Question 1

What is the equation for the emf generated by a loop of wire?

Answer 1

ε = -dф/dt, where ф is the magnetic flux through the loop of wire

Question 2

What is the magnetic flux through a loop of wire equal to?

Answer 2

ф = BA*cos(ωt+Ф)

Question 3

What is the final equation for the emf generated by a loop of wire?

Answer 3

ε = BNAω*sin(ωt+Ф), where ω is the angular velocity, N is the number of loops, A is the area and Ф is the phase

Question 4

What are the 3 equations for voltage in a 3-phase AC system?

Answer 4

V1 = V0*cos(ωt)
V2 = V0*cos(ωt+2π/3)
V3 = V0*cos(ωt+4π/3)

V1+V2+V3 = 0

Question 5

What is an equation for power including voltage and resistance?

Answer 5

P = V^2/R

Question 6

What is High Voltage Direct Current?

Answer 6

HVDC is used to connect networks on different phases, run cables underwater and over large distances and integrates into renewable sources

Question 7

What is the equation for energy loss in heat from electrical transmission?

Answer 7

ε = I^2*R

Question 8

What is the equation for the resistanceof a wire?

Answer 8

R = nL/A, where n is the resistivity, L is the length and A is the cross section

Question 9

What are transformers made up of?

Answer 9

2 coils of wire, insulated but sharing common magnetic flux, one with more coil turns than the other.

Question 10

What is the ratio of emfs for the two coils in a transformer equal to?

Answer 10

ε1/ε2 = N1/N2, where N is the number of coil turns.

Question 11

How would you work out the step up or step down voltage for a transformer?

Answer 11

V2 = V1*N2/N1

Question 12

What is the sun Earth distance in AU and km?

Answer 12

1AU = 150*10^6 km

Question 13

What is the approximate temperature and radius of the sun?

Answer 13

T = 6000 K
R = 7*10^5 km

Question 14

What is the equation for flux?

Answer 14

power/area = σ*T^4

Question 15

What is the equation for the power absorbed from the sun at distance 1AU?

Answer 15

P = σ*T^4 * R^2/R(AU)^2 *f

where f is the albedo of Earth (some energy radiated by Earths atmosphere)

Question 16

What is the equation for power to the surface of a solar panel?

Answer 16

P = σAT^4 * R^2/R(AU)^2 *f

Question 17

What is the equation for the temperature of the solar panel surface?

Answer 17

T = T(sun)*(R(sun)/R(AU))^1/2 * f^1/4

Question 18

What is the equation for magnification from a perfect spherical mirror?

Answer 18

m = di/do, where di is the distance to the image and do to the object

Question 19

What is the equation for the area of the image reflected from a perfect spherical mirror?

Answer 19

(r(mirror)/2R(au)_^2 * π*R(sun)^2

,where r(mirror)/2 is the mirrors focal length and r(mirror) is the radius of curvature

Question 20

How do you get an equation for Tmax, the max temperature of the mirror?

Answer 20

Equate power to surface of mirror = power radiated at the focus, and rearrange for Tmax

Question 21

What is the equation for Q(H) in a carnot cycle if Q(Sun) is the input heat?

Answer 21

Q(H) = Q(Sun) - Q(radiated) = σT(sun)^4 - σT^4

Question 22

What is the equation for the carnot efficiency of this system?

Answer 22

n = W/Q(H) = 1-T(C)/T

so W = Q(H)*(1-T(c)/T)

Question 23

What is the equation for the overall efficiency of this system?

Answer 23

ε = W/Q(Sun) = Q(H)*(1-T(c)/T)/Q(Sun) = T(Sun)^4-T^4/T(Sun)^4 X (1-T(c)/T)