Question

An AA battery provides 1.5v and up to 0.8 amps of output current. A portable communication device needs 4 volts and 1 amp. What is the minimum number of AA batteries that are needed to power this equipment?
a. 3
b. 4
c. 5
d. 6
e. 7

A 0.4 meter * 0.5 meter solar panel delivers 2 Amp current while maintaining the output voltage at 12V when it is exposed to a direct sunlight at 1,000 W/m^2 power density. What is the efficiency of this panel in this operating condition?

a. 12%
b. 15%
c. 18%
d. 20%
e. 22%

A digital picture frame consumes .5W of power in the standby mode (5W in the normal mode). Approximately 20 million frames have been sold in the US. If all the frames are plugged in year-round, how many IMW wind turbines are required to generate enough energy just to keep these frames in the standby mode? Assume the wind turbines produce IMW only during 8 hours each day.

a. 1
b. 3
c. 10
d. 30
e. 50

Answer 1

Question 1

Power consumed by single battery = 1.5 * 0.8 = 1.2 W

Power required by communication device = 4 * 1 = 4 W

Therefore minimum batteries required = floor of 4/1.2 = floor of 3.33 = 4

Question 2

Area of solar panel = 0.4 *0.5 = 0.2 sq. m

Power of solar panel = 2 * 12 = 24 W

Therefore, efficiency of solar panel = Output power / input power = 1000 * 0.2/24 = 20.83 ~ 20 %

Question 3

Information insufficient. Parameters to compute power of single turbine are missing.