Two wires $$A$$ and $$B$$ of equal lengths are connected in left and right gap of a meter bridge, null point is obtained at $$40 \mathrm{~cm}$$ from left end. Diameters of the wire $$A$$ and $$B$$ are in that ratio $$3: 1$$. The ratio of specific resistance of $$A$$ to the of $$B$$ is

When a small amount of impurity atoms are added to a semiconductor, then generally its resistivity

When open pipe is closed from one end third overtone of closed pipe is higher in frequency by $$150 \mathrm{~Hz}$$, then second overtone of open pipe. The fundamental frequency of open end pipe will be

A ray of light is incident at an angle $$i$$ on one face of prism of small angle $$A$$ and emerges normally from the other surface. $$\mu$$ is the refractive index of the material of the prism. The angle of incidence is