NEET Practice Questions (MCQs) with Answers & Solutions

The NCERT text (Wave Optics, page 259) states: 'From the above equation, we get the important result that if $r < i$ (i.e., if the ray bends toward the normal), the speed of the light wave in the second medium ($v_2$) will be less then the speed of the light wave in the first medium ($v_1$).' This is a direct consequence of Snell's law $n_1 \sin i = n_2 \sin r$ and $n = c/v$, which implies $ \frac{\sin i}{\sin r} = \frac{n_2}{n_1} = \frac{v_1}{v_2} $. If $v_2 < v_1$, then $ \frac{v_1}{v_2} > 1 $, so $ \frac{\sin i}{\sin r} > 1 $, which means $\sin i > \sin r$, and thus $i > r$ (for acute angles).

The introductory paragraph of Chapter 9 (Ray Optics and Optical Instruments) states: 'In this chapter, we consider the phenomena of reflection, refraction and dispersion of light, using the ray picture of light. Using the basic laws of reflection and refraction, we shall study the image formation by plane and spherical reflecting and refracting surfaces.' This clearly defines the scope and approach of ray optics.

The NCERT text explicitly states: 'We have, for small angles, $\tan \angle NOM = \frac{MN}{OM}$'. This is a direct application of the small angle approximation where $\tan \theta \approx \theta \approx \sin \theta$ and relating it to the sides of the right-angled triangle formed by the perpendicular from N to the principal axis.

According to the NCERT text, 'A reversible process proceeds infinitely slowly by a series of equilibrium states such that system and the surroundings are always in near equilibrium with each other.' It also states that 'A process is reversible only if it is quasi-static (...) and there are no dissipative effects.' Therefore, the presence of significant dissipative effects is not characteristic of a reversible process.

The NCERT text states, 'From the preceding discussion, a reversible process is an idealised notion. A process is reversible only if it is quasi-static (system in equilibrium with the surroundings at every stage) and there are no dissipative effects.' These ideal conditions are rarely met in real-world processes, making it an idealised concept.

The NCERT text explicitly states, 'The base of a vessel on an oven is hotter than its other parts. When the vessel is removed, heat is transferred from the base to the other parts, bringing the vessel to a uniform temperature... The process cannot be reversed; a part of the vessel will not get cooler spontaneously and warm up the base.' Options o1, o3, and o4 describe characteristics or examples of reversible processes.

The NCERT states, 'Irreversibility arises mainly from two causes: one, many processes (like a free expansion, or an explosive chemical reaction) take the system to non-equilibrium states; two, most processes involve friction, viscosity and other dissipative effects.' These factors make processes irreversible.

According to the NCERT (Chemistry) text, for isothermal reversible change, $w_{rev} = -nRT \ln(V_f/V_i) = -2.303 nRT \log(V_f/V_i)$. Option o1 is for irreversible work, and o2 has the wrong sign. Option o4 is for heat at constant volume.

The NCERT (Chemistry) text states: 'Free expansion: Expansion of a gas in vacuum ($p_{ex} = 0$) is called free expansion. No work is done during free expansion of an ideal gas whether the process is reversible or irreversible ($w=0$ since $p_{ex}=0$). Also, Joule determined experimentally that $q=0$; therefore, $\Delta U = 0$.'

The NCERT (Physics) text states: 'A heat engine based on idealised reversible processes achieves the highest efficiency possible. All other engines involving irreversibility in any way (as would be the case for practical engines) have lower than this limiting efficiency.'