A lamp placed at a distance of 50.0 cm from a screen on one side produces the same illumination as a standard 60 cd candle placed 100 cm away on the other side of the screen. What is the luminous intensity of the lamp?



Correct option is

15 cd


I1 = ?, I2 = 60 cd, r1 = 50.0 cm and r2 = 100 cm. According to the principle of photometer, two sources will produce equal illumination of the screen if 




A beaker is filled with water to a height of 8.00 cm. The apparent depth of a needle fixed at the bottom of the beaker as measured by a travelling microscope is found to be 6.00 cm. If the height of water in the beaker is increased to 12.0 cm, by what distance would the microscope have to be moved to focus on the needle again?       


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The polarising angle for glass is 


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