What is an emission spectrum?

What is the primary process by which light is emitted in an emission spectrum?

What role does a prism play in the formation of an emission spectrum?

If a line in an emission spectrum has a wavelength of 500. nm, what is the frequency of this light? (Use c = 3.00 x 10⁸ m/s)

If a photon has a wavelength of 600. nm, what is its energy? (Use h = 6.63 x 10^-34 J·s and c = 3.00 x 10⁸ m/s)