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A ray of light intensity I is incident on a parallel glass slab and refraction. At each reflection, 25% of incident energy is reflected. The rays AB and AB undergo interference. The ratio of Imax and Imin is
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A. 49:1
B. 7:1
C. 4:1
D. 8:1

Answer
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Hint:
Here first we have to find the value of AB and AB and then the ratio of AB and AB .At last we have to find the ratio of Imax and Imin

Complete step by step solution:
Given,
A ray of light intensity I is incident on a parallel glass slab and refraction.
At each reflection, 25% of incident energy is reflected.
The rays AB and AB undergo interference.
Since, I is incident on a parallel glass slab and 25% incident energy is reflected.
So, AB=I4
AC=(10025)%×I=75%×I=3I4
AC=75%×25%I=3I16
AB=75%×25%×75%I=9I64
Now let I1=I4 and I2=9I64
Now let us find the ratio of Imax and Imin
ImaxImin=(I2I1+1I2I11)2ImaxImin=(916+19161)2ImaxImin=491
So, the ratio of Imax and Imin is 491

Hence, option A is correct.

Additional information:
Total internal reflection and critical angle- In optics total internal reflection is the complete reflection of a beam of light in a medium such as water or glass back onto the medium from the surrounding surfaces. If the angle of incidence is greater than a certain limiting angle, called the critical angle, the phenomenon of total internal reflection occurs.
Reflection on a glass slab- As light penetrates the glass slab through air, they are refracted and bend towards the normal. The path of the refracted ray now shifts again as it comes into the air from the glass plate. If the beam of light passes from a denser to a rarer medium, it bends away from the normal.

Note:
Here we have to keep in mind that at each reflection, 25% incident energy is reflected. So, the value of each incident ray will be different. Also for the formula of ImaxImin=(I2I1+1I2I11), we cannot swap the numerator and denominator in confusion. So, we have to be very careful while solving this.

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