Question

Two coherent sources of equal intensity produce maximum intensity of 100 units at a point. If the intensity of one of the sources is reduced by $36\%$ reducing its width, then the intensity of light at the same point will be

• A. 90
• B. 89
• C. 67
• D. 81

Answer 1

Answer: (D)

Intensity of each source $=I_0=\frac{100}{4}=25$ unit
If the intensity of one of the source is reduced by $36\%$ then $I_1=25$ unit and
$I_2=25-25\times \frac{36}{100}=16($ unit $)$
Hence resultant intensity at the same point will be
$I=I_1+I_2+2\sqrt{I_1{I}_2}$
$=25+16+2\sqrt{25\times 16}=81$ unit