Are coherent and incoherent waves visible to the human eye?

Can we convert a coherent wave into an incoherent wave (or vice versa)?

In Young double slit experiment the n^th red bright band coincide with (n + 1)^th blue bright band. If the wavelength of red and blue light are 7500 Å and 5000 Å, then the value of ‘n’ is

Activity of radioactive element decrease to one-fourth of original activity R₀ in 16 years, after further 16 years, its activity will be  

Figure shows a mixture of blue, green and red coloured rays incident normally on a right angled prism. The critical angles of the material of the prism for red, green and blue are 46º, 44º and 43º respectively. The arrangement will separate

The fringe width in Young’s double slit experiment increases when