Optics (Physics) Part-III

Total Questions: 56

51. Three colours are the primary colours. These are - [M.P.P.C.S. (Pre) 2005]

Correct Answer: (b) Blue, Green and Red
Solution:

Black is not a primary colour. In painting red, yellow and blue are primary colours. But in terms of physics and light, primary colours are red, green and blue.

52. Consider the following statements: [I.A.S. (Pre) 2007]

1. If magenta and yellow coloured circles intersect, the intersected area will have a red colour.

2. If cyan and magenta coloured circles intersect, the intersected area will have a blue colour.

Which of the statements given above is/are correct?

Correct Answer: (c) Both 1 and 2
Solution:

If we mix red, green and blue colour, we get the white colour. Red, green and blue is referred to as the primary colors. Similarly cyan, magenta and yellow are referred to as the primary pigment colors. If we mix magenta and yellow we get the red colour.

Hence, statement 1 is correct. Similarly if cyan and magenta colours are mixed together we get blue color. Thus, statement 2 is also correct. If we mix cyan and yellow we get the green colour.

53. Match List-l with List-II: [69ᵗʰ B.P.S.C. (Pre) 2023]

List–I (Colour)List–II (Combination)
A. Magenta1. Green and blue
B. Teal2. Red and blue
C. Mauve3. Blue, green and white
D. Cyan4. Blue, red and white
ABCD
(a)2341
(b)2431
(c)4213
(d)3421

Select the correct answer using the codes given below.

Correct Answer: (a)
Solution:

The correctly matched lists are as follows:

ColourCombination
A. Magenta1. Red and blue
B. Teal2. Blue, green and white
C. Mauve3. Blue, red and white
D. Cyan4. Green and blue

54. The number of colours contained in the sunlight is - [U.P.P.C.S. (Mains) 2015]

Correct Answer: (d) 7
Solution:

As we all know the sunlight is a white light and it consists of seven colours. The splitting of light into its different components (VIBGYOR) i,e, violet, indigo, blue, green, yellow, orange and red is called the dispersion of light. A prism is used to disperse light into its different components

55. Find out the odd colour from the following options- [R.A.S./R.T.S. (Pre) 1999]

Correct Answer: (b) Brown
Solution:

The brown color is an odd colour. It is because of the concept of VIBGYOR. As we know that white light is the mixture of seven colours- red, orange, yellow, green, blue, indigo and violet. Thus brown doesn't belong to this combination.

56. Consider the following phenomena: [I.A.S. (Pre) 2013]

1. Size of the Sun at dusk

2. Colour of the Sun at dawn

3. Moon being visible at dawn

4. Twinkle of stars in the sky

5. Polestar being visible in the sky

Which of the above are optical illusions?

Correct Answer: (c) 1, 2 and 4
Solution:

The size of the Sun at dusk is an optical illusion. The Sun appears smaller during noon but longer at dawn or more clearly at dusk. At dawn, the Sun is seen with other objects on the horizon and looks big.

The colour of the Sun at dawn is also an optical illusion. Finally twinkling of stars is also an optical illusion caused by the refraction of light while moving through various layers of atmosphere.