KVPY Government Jobs Exams

A parent nucleus X is decaying into daughter nucleus Y which in turn decays to Z. The half lives of X and Y are
40000 years and 20 years respectively. In a certain sample, it is found that the number of Y nuclei hardly changes
with time. If the number of X nuclei in the sample is 4 × 1020, the number of Y nuclei present in its is

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KVPY Other Question

A cylindrical steel rod of length 0.10 m and thermal conductivity 50 W.m–1 K–1 is welded end to end to copper
rod of thermal conductivity 400 W.m–1. K–1 and of the same area of cross section but 0.20 m long. The free end of
the steel rod is maintained at 100º C and that of the copper and at 0º C. Assuming that the rods are perfectly
insulated from the surrounding, the temperature at the junction of the two rods An unpolarized beam of light of intensity I0 passes through two linear polarizers making an angle of 30º with
respect to each other. The emergent beam will have an intensity