Physics MCQs for NEET — Practice Questions with Answers

As described in NCERT Section 10.3.1 (Wave Optics) and depicted in Figure 10.7(b): 'In Fig. 10.7(b) we consider a plane wave incident on a thin convex lens; the central part of the incident plane wave traverses the thickest portion of the lens and is delayed the most. The emerging wavefront has a depression at the centre and therefore the wavefront becomes spherical and converges to the point F which is known as the focus.' This illustrates the application of Huygens' principle to lens behavior.

From the NCERT text, 'The rays are incident from a medium of refractive index $n_1$, to another of refractive index $n_2$.' (Section 9.5.1). Therefore, $n_1$ is the refractive index of the medium of incidence.

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.