What is the main reason why people use machines

Starting with only the balmer series light (visible light), how could we ensure that the solar panels generate a current that mark can use for his power station? a)by gradually increasing the brightness (amount) of light that we shine on it. b)by gradually increasing the frequency of the light we shine on it. c)by gradually increasing the wavelength of the light that we shine on it.

The air that we breath is made mostly of which gaseous molecule

A2k pendulum has a speed of 1 m/s at a height of 1/2 meter