M.C.Q-[Phy-1M]

MCQ 11 Mark

In the following diagram showing dispersion of white light by a glass prism, the colours $\mathbf{P}$ and $\mathbf{Q}$ respectively are-

✓
Violet and Red
B
Orange and Green
C
Red and Blue
D
Red and Violet

Answer

Correct option: A.

Violet and Red

(A) Violet and Red
Explanation: The splitting of white light into its constituent colours is known as light dispersion. The spectrum is the band of seven colours produced by splitting white light. All of the constituent colours of white light have the same velocity in vacuum, but their velocity changes when they pass through a transparent 'medium' like a glass prism. Different colours are diverted by different angles on the prism's initial face. Violet's minimum speed is deviated by the maximum angle, whereas red's maximum speed is distorted by the minimum angle. As a result, the letters ' P ' and ' Q ' are violet and crimson, respectively.

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MCQ 21 Mark

Which of the following statements is true?

A
A concave lens has 4 dioptre power having
B
A concave lens has-8 dioptre power having a focal length 0.25 m a focal length of 0.25 m
C
A convex lens has -4 dioptre power having a focal length 0.25 m
✓
A convex lens has 4 dioptre power having a focal length 0.25 m

Answer

Correct option: D.

A convex lens has 4 dioptre power having a focal length 0.25 m

(D) A convex lens has 4 dioptre power having a focal length 0.25 m
Explanation: The power P of a lens of the focal length is given by $P=\frac{1}{f}$, where f is the focal length in meter and power in dioptre $P=\frac{1}{f}$ orf $=\frac{1}{P}=\frac{1}{4}=0.25 \mathrm{~m}$
The positive value for focal length indicates a convex lens.

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