In amplitude modulation,

When a photon enters glass from air, which one of the following quantity does not change?

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