Question

If a newton’s colour disc composed of seven colours is rotated at a high speed, it appears as:
(A) Seven coloured disc rotating
(B) Few colours merge and only three dominant colours are visible
(C) Colours mix as it appears white
(D) Colours mix giving rise to a sparkling effect

Answer 1

Hint: We know that Newton's colour disc consists of seven colours (VIBGYOR) and when the disc it rotated at a very high speed, it appears as if all colours are mixed. It is known to us that, when all colours are mixed, it appears as white.

Complete Step-By-Step Solution:
Newton disc is a very well-known experiment, in which seven colours namely violet, indigo, blue, green, yellow, orange and red are placed in a pie chart form on a disc, and the disc is rotated.
It is observed that, when the disc is rotated at a high speed, the colour seen by human eyes is only a single colour which is white.
The colour of the entire disc appears as white, because all colours when mixed gives the colour white. The colours mix due to high speed rotation. This mixing of colour is known as temporal optical mixing.
This also suggests that human eyes cannot differentiate between different colors when they move at a high speed.
Thus, white light comprises seven colours.
Hence, when a newton’s colour disc composed of seven colours is rotated at a high speed, it appears as Colours mix as it appears white.

Therefore, option (C) is correct.

Note:
Similar phenomenon is also seen in the case of prisms. Newton concluded that, when white falls on a prism, light gets detracted through different angles which gives rise to seven different colours. The refraction in a prism occurs at two points, when the light enters the prism as well as when the light moves out of the prism.