For a wavelength at the peak of visual sensitivity, 550 nm, how many photons lead to an observable flash

Copper has free electrons per cubic meter. a 71.0-cm length of 12-gauge copper wire that is 2.05 mm in diameter carries 4.85 a of current. (a) how much time does it take for an electron to travel the length of the wire? (b) repeat part (a) for 6-gauge copper wire (diameter 4.12 mm) of the same length that carries the same current. (c) generally speaking, how does changing the diameter of a wire that carries a given amount of current affect the drift velocity of the electrons in the wire?

Anybody wanna ? (picture included? )

Ascientist wants to test ways to reduce pollution in lake . what is the bestway of doing this