Answered

Calculate the maximum kinetic energy of photoelectrons emitted from this plate when light of wavelength (λ) 520nm is directed at the metal surface.

Work function (Ф) of the plate = 1.1 × 10⁻¹⁹ J
Planck's constant (h) = 6.63 × 10⁻³⁴ Js
Frequency (f) = c ÷ λ
c = speed light in vacuum = 3.00 × 10⁸ms⁻¹
Ekmax = hf - Φ

Wavelength must be in metres, so it'll be 590×10⁻⁹

I've worked this out and gotten two different answers so I thought I'd check to see which one is right.

Answer :

Well for a start, 520nm is 520 nanometres and for some reason you've called it 590 x10^-9 (590 isn't standard form) where it's actually 5.2 ×10^-7 metres.
Put that into the equations:
f = c/λ = 3.0 x10^8/5.2 ×10^-7 = 5.77 x10^14 (3 s.f.)
(5.77 x10^14) x (6.63 x10^-34) - (1.1 x10^-19) =
2.73 x10^-19 J