If $$13.6$$ $$eV$$ energy is required to ionize the hydrogen atom, then the energy required to remove an electron from $$n=2$$ is

If two mirrors are kept at $${60^ \circ }$$ to each other, then the number of images formed by them is

If $${\theta _1},$$ is the inversion temperature, $${\theta _n}$$ is the neutral temperature, $${\theta _c}$$ is the temperature of the cold junction, then

On moving a charge of $$20$$ coulomb by $$2$$ $$cm,$$ $$2$$ $$J$$ of work is done, then the potential differences between the points is