According to Bohr's principle,the relation between principal quantum number $(n)$ and the radius of the orbit $(r)$ is:

When light is directed at the metal surface,the emitted electrons

Which of the following electron transitions in a hydrogen atom will require the largest amount of energy?

The number of absorption lines in the given figure will be .......

Consider an electron moving in the first Bohr orbit of a $He^{+}$ ion with a velocity $v_1$. If it is allowed to move in the third Bohr orbit with a velocity $v_3$, then indicate the correct $v_3: v_1$ ratio.

Find the value of wave number $(\bar{v})$ in terms of Rydberg's constant,when the transition of an electron takes place between two levels of $He^{+}$ ion whose sum is $4$ and difference is $2$.