NEET Practice Questions (MCQs) with Answers & Solutions

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.'

The context states: 'ultraviolet light gives rise to photoelectric effect in copper while green or red light does not.' This indicates that the frequency of ultraviolet light is above copper's threshold frequency, while the frequencies of green and red light are below it, as lower frequencies mean longer wavelengths and vice versa.

If $\nu < \nu_0$, then $h\nu < h\nu_0$, which means $h\nu - \phi_0$ would be negative. Since kinetic energy cannot be negative, this indicates that no photoelectric emission takes place, consistent with the definition of threshold frequency.

The pyramid of energy is always upright because according to the 10% law, only 10% of the energy is transferred from one trophic level to the next. This means there is always less energy at higher trophic levels than at lower ones, making an inverted energy pyramid impossible. Pyramids of number and biomass can be inverted in certain ecosystems.

As stated in the text, 'The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top-level consumer.'

The exercise question asks: 'In an ecosystem dominated by trees, the pyramid (of numbers) is_________type.' This implies an inverted pyramid of numbers. A single large tree can support many herbivores (e.g., insects), which in turn support fewer carnivores, leading to an inverted shape.

The text clearly states, 'However, there are certain limitations of ecological pyramids such as it does not take into account the same species belonging to two or more trophic levels. It assumes a simple food chain, something that almost never exists in nature; it does not accommodate a food web.'