3(a)
The wave lengths for the light of red and blue colours are nearly 7.8 x 10-7 m and 4.8 x 10-7 m respectively.
(i) Which colour has the greater speed in a vacuum?
(ii) Which colour has a greater speed in glass?
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(i) The speed is same for both colours in vacuum because velocity of light of all colors in vacuum or air remains the same and it changes only when the medium changes.
(ii) The light of red colour has greater speed in glass as it has a larger wavelength.