If the wave length of light in an experiment on photo electric effect is doubled keeping the intensity constant,

The relationship between wavelength and stopping potential are given as below:

${\mathrm{V}}_0 = \frac{\mathrm{hc}}{\mathrm{\lambda e}} - \frac{\mathrm{\phi }}{\mathrm{e}}$

where V₀ = stopping potential, $\lambda =$wavelength.

If the wavelength of the light is doubled, the stopping potential decreases according to the equation. 

If wavelength is doubled, there is possibility that new wavelength will be greater than threshold wavelength because of which electrons may be or may not be emitted from the surface.

Photocurrent depends only on the intensity if the electrons are emitted, so if intensity is kept constant, then photocurrent will not change.