The work function for Aluminium surface is 4.2 eV. Find the threshold wavelength for the photoelectric emission.

2959 Å 4200 Å 4736 Å 5890 Å

2959 Å

Threshold Wavelength is $ \lambda_0 = \frac{hc}{\phi} = \frac{12400 A^o}{4.2} = 2959 A^o$