Tag: speed of light and optical density

Questions Related to speed of light and optical density

When light is refracted into a denser medium,

physics refraction of light the nature of light speed of light and optical density introduction to light

  1. its wavelength and frequency both increase

  2. its wavelength increases but frequency remains unchanged

  3. its wavelength decreases but frequency remains unchanged

  4. its wavelength and frequency both decrease

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Correct Option: C
Explanation:

$ _1\mu _2 = \dfrac{v _1}{v _2} = \dfrac{v _{rarer}}{v _{denser}} \Rightarrow v _1 > v _2$


$\Rightarrow v _1 > v _2$


$\Rightarrow \lambda _1 f _1 > \lambda _2 f _2$
Where $f$ is the frequency

when light goes from any rarer to any denser medium frequency remain unchanged.

$\therefore f _1 = f _2 = f$

$\Rightarrow \lambda _1 > \lambda _2$

hence wavelength decreases but frequency remains unchanged. 

Option C is correct.

Mark the correct statements (s) for a very thin soap film (RI = 1.33) whose thickness is much less then wavelength of visible light.

physics refraction of light the nature of light speed of light and optical density introduction to light

  1. Film appears dark.

  2. Film appears shiny.

  3. Film on glass (RI = 1.5) appears dark.

  4. Film on glass (RI = 1.5) appears shiny.

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Correct Option: C

When a ray of light enters glass from water, it bends :

physics refraction of light the nature of light speed of light and optical density introduction to light

  1. Away from the normal due to increase in the speed of light

  2. Away from the normal due to decrease in the speed of light

  3. Towards the normal due to decrease in the speed of light.

  4. Towards the normal due to increase in the speed of light.

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Correct Option: D
Explanation:

When a ray of light enters from glass to water, it bends towards normal due to increase in speed of light. 

As we know,

          $\mu=\dfrac{c}{v}$

         $\mu$ for water is less than that of glass, as glass acts as a denser medium. $\therefore$ the speed of light in glass will be less than that in water.

A convex lens forms a real image with magnification $m _1$ on a screen. Now, the screen is moved by a distance x and the object is also moved so as to obtain a real image with magnification $m _2 (> m _1) $ on the screen. Then, the focal length of the lens is

physics refraction of light the nature of light speed of light and optical density introduction to light

  1. $\left [ \dfrac{m _1}{m _2} \right ]x$

  2. $\left [ \dfrac{m _2}{m _1} \right ]x$

  3. $x(m _2-m _1)$

  4. $ \dfrac{x}{(m _2-m _1)} $

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Correct Option: D