1.the count of alpha particles decreases from 28800 to 1800 in 48 hrs.the half life of this radioactive element   is ?

2.if a transparent slab of refractive index is u=1.5 and thickness t = 2.5 X 10^-5 m is inserted in front of one of the slits of youngs double slit exp. how much will be the shift in interference pattern?The distance between the slit is 0.5mm and that between slit and screen is 100cm.  (ans 2.5cm)

3.A transparent cube contains a small air bubble.Its apparent  distance is 2cm when seen through one face and 5cm when seen through other face.if refractive index of the material is of the cube is 1.5,then real lenght of the edge of cube must be: ? (ans 10.5cm)

1)A=A₀(1/2)ⁿ where n is the no.of half lives.Put A=28800,A₀=1800,we get n=4.So,t_1/2=12hrs.

2)shift=(k-1)tD/d=(0.5)(2.5X10^-5)(1)/0.5x10^-3=2.5X10^-2m=2.5cm