Harmonics problem. A square wave of frequency f contains harmonics (sine waves) at f, 3f, 5f, 7f, ... . Suppose a system responds to frequencies in the range 20-40 kHz but is insensitive outside of this range.
EXAMPLE:
Imagine applying a square wave with f = 30 kHz to this system. What is the shape of the response?
[ a 30 kHz sine wave. ]
Imagine applying a square wave with f = 10 kHz to this system.

What is the shape of the response?
A. A 10 kHz sine wave
B. A combination of 20, 30 and 40 kHz sine waves
C. A 30 kHz sine wave
D. No response

C.

Explanation:

-first use of geothermal energy occurred more than 10,000 years ago in north america by american paleo-indians

-the first industrial use of geothermal energy began near pisa, italy in late 18th century

-in 1904, italian scientist piero ginori conti invented the first geothermal electric power plant in which steam was used to generate the power

-with the above experiment, the first geothermal plant in usa started in 1922 with a capacity of 250 kilowatts

-however, in 1946 first ground-source geothermal heat pump installed at commonwealth building in portland, oregon

-during the 1960’s, pacific gas and electric began operation of first large scale geothermal power plant in san francisco, producing 11 megawatts

-in 1973, when oil crisis began many countries began looking for renewable energy sources and by 1980’s geothermal heat pumps (ghp) started gaining popularity in order to reduce heating and cooling costs

-as effect of climate change started showing results, governments of various countries joined hands to fight against it, for which kyoto protocol was signed in japan in 1997, laid out emission targets for rich countries and required that they transfer funds and technology to developing countries, 184 countries have ratified it

hope this

the answer is 12 as i may remember

: )