Question

why does the white light split on the first refracting face of prism

Answer 1

white light has 7 different colors of different wavelength. they travell in air with the same speed . however there speed changes in other medium as they have different wavelengths. the differential change of theit speed on entering the prizm cause the white light to split into 7 .

Answer 2

white light is a combination of 7 colours. when it is passed through prism, they are refracted. all colours have different wavelengths. since they have different wavelengths, they are dispersed.