For potassium metal, the work function φ (the minimum energy needed to eject an electron from the metal surface) is 3.68 × 10–19 j. which is the longest wavelength of the following which could excite photoelectrons?
a. 550nm
b.500nm
c.450nm
d.400nm
e.350nm

A.

Explanation:

The work function of the potassium =

For maximum wavelength, the light must have energy equal to the work function. So,

Where,  

h is Plank's constant having value

c is the speed of light having value

is the wavelength of the light being bombarded

Thus,

Also,  

1 m = 10⁻⁹ nm

So,  

what is the general relationship between a galaxy's distance from earth and its speed?

the answer is:

the farther away a galaxy is from us, the faster it is moving away from us.