Atomic Structure MCQs for NEET — Chemistry Questions with Answers

The text defines it as: 'This minimum, cut-off frequency $\nu_0$, is called the threshold frequency. It is different for different metals.' And 'Below a certain frequency (threshold frequency) $\nu_0$, characteristic of the metal, no photoelectric emission takes place, no matter how large the intensity may be.'

The text explicitly states: 'It is now known that emission starts in a time of the order of $10^{-9}$ s or less.' This indicates the instantaneous nature of the process.

The text mentions: 'However, some alkali metals such as lithium, sodium, potassium, caesium and rubidium were sensitive even to visible light.' Zinc and cadmium are mentioned as responding to ultraviolet light.

Einstein’s photoelectric equation is given as: '$1/2 m v^2_{max} = V_0 e = h\nu – \phi_0 = h (\nu – \nu_0)$'. Here, $\phi_0$ represents the work function, which is $h\nu_0$.

Point 4 in the summary states: 'The stopping potential ($V_0$) depends on (i) the frequency of incident light, and (ii) the nature of the emitter material. For a given frequency of incident light, it is independent of its intensity.'

Figure 11.4 and its description state: 'The stopping potential is more negative for higher frequencies of incident radiation.' This implies that as frequency increases, the stopping potential increases in magnitude (becomes more negative). This is also consistent with $V_0 = (h/e)(\nu - \nu_0)$, where $h/e$ is positive.

Point 6 in the summary states: 'The classical wave theory could not explain the main features of photoelectric effect. Its picture of continuous absorption of energy from radiation could not explain the independence of $K_{max}$ on intensity, the existence of $\nu_0$ and the instantaneous nature of the process.' All listed options are correct reasons for its failure.

The text describes the setup: 'The polarity of the plates C and A can be reversed by a commutator. Thus, the plate A can be maintained at a desired positive or negative potential with respect to emitter C.'

Figure 11.3 demonstrates this: 'We note that the saturation currents are now found to be at higher values' when intensity is increased (I3 > I2 > I1 corresponds to higher saturation currents). The photoelectric current is directly proportional to the number of photoelectrons emitted per second, which in turn is proportional to the intensity.

The text clearly states: 'Photoelectric effect involves conversion of light energy into electrical energy.'