Subject

Science

Class

CBSE Class 10

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsLong Answer Type

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41.

State the law of refraction of light that defines the refractive index of a medium with respect to the other. Express it mathematically. How is refractive index of any medium 'A' with respect to a medium 'B' related to the speed of propagation of light in two media A and B? State the name of this constant when one medium is vacuum or air.

The refractive indices of glass and water with respect to vacuum are 3/2 and 4/3 respectively. If the speed of light in glass is 2 ×  m/s, find the speed of light in (i) vacuum, (ii) water.


First law of refraction also known as Snell’s law defines the refractive index of a medium with respect to the other medium.

First law of refraction states that, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. This is known as Snell’s law.

Mathematically, it can be given as follows:
fraction numerator Sin space straight i over denominator Sin space straight r end fraction space equals space c o n s tan t space equals mu presuperscript a subscript b

 

Here,  straight mu presuperscript straight a subscript straight bis the relative refractive index of medium b with respect to medium a.

Consider a ray of light travelling from medium B into medium A. Let v1 be the speed of light in medium A and v2 be the speed of light in medium B. Then,

Refractive index of medium A with respect to medium B is given by

 straight n subscript AB space equals straight v subscript 2 over straight v subscript 1

If one medium is vacuum or air then the constant is known as absolute refractive index of the medium.

 
Let comma space absolute space refractive space index space of space glass comma space straight n subscript straight g space equals space 3 over 2
Absolute space refractive space index space of space Water space straight n subscript straight w space equals 4 over 3

speed space of space light space in space glass comma space straight v subscript straight g space equals space 2 space straight x space 10 to the power of 8 space straight m divided by straight s

straight i right parenthesis space speed space of space light space in space vacuum

straight n subscript straight g space equals straight c over straight v subscript straight g

straight c equals space straight n subscript straight g space straight x space straight v subscript straight g space equals 3 over 2 space straight x space 2 space straight x space 10 to the power of 8 space straight m divided by straight s

ii right parenthesis space Speed space of space light space in space water comma

straight n subscript straight w space equals straight c over straight v subscript straight w

straight v subscript straight w space equals straight c over straight n subscript straight w space equals fraction numerator space 3 space straight x space 10 to the power of 8 over denominator 4 divided by 3 end fraction space equals 2.25 space straight x space 10 to the power of 8 space straight m divided by straight s

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42.

What is the difference between the chemical composition of soaps and detergents? State in brief the action of soaps in removing an oily spot from a shirt. Why soaps are not considered suitable for washing where water is hard?

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43.

List in tabular form three physical and two chemical properties on the basis of which ethanol and ethanoic acid can be differentiated.

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