The activity of a radioactive sample is measured as No counts per minute at $$t=0$$ and $$\mathrm{N}_0 / \mathrm{e}$$ counts per minute at $$t=6 \mathrm{~min}$$. The time (in minutes) at which the activity reduces to half its value is.
A ball is allowed to fall from a height of $$10 \mathrm{~m}$$. If there is $$30 \%$$ loss of energy due to impact, then after one impact ball will go up to.
The elastic limit of $$1 \mathrm{~kg}$$ mass is $$3.5 \times 10^{10} \mathrm{~N} / \mathrm{m}^2$$. Find the maximum load that can be applied to a brass wire of a $$1 \mathrm{~mm}$$ diameter without exceeding the elastic unit.
The focal length of thin convex lens for red and blue rays are $$100 \mathrm{~cm}$$ and $$98.01 \mathrm{~cm}$$, respectively. There, the dispersive power of the material of the lens is