Physics MCQs for NEET — Practice Questions with Answers

Figure 2.3 (b) is described as 'Motion in positive direction with negative acceleration'. This graph shows a straight line with a negative slope (negative acceleration), meaning velocity decreases over time, but it starts with a positive velocity (moving in the positive direction).

The text states, 'Since velocity is a quantity having both magnitude and direction, a change in velocity may involve either or both of these factors. Acceleration, therefore, may result from a change in speed (magnitude), a change in direction or changes in both.'

Figure 2.4 (c) shows a position-time graph as a straight line, and it is explicitly labeled as 'zero acceleration'. The text also states, 'it is a straight line for zero acceleration' in the context of position-time graphs.

As per the NCERT text, 'A locus of points, which oscillate in phase is called a wavefront; thus a wavefront is defined as a surface of constant phase.' Option o3 directly matches this definition.

The NCERT states, 'Thus, if we wish to determine the shape of the wavefront at t = t, we draw spheres of radius vt from each point on the spherical wavefront where v represents the speed of the waves in the medium. If we now draw a common tangent to all these spheres, we obtain the new position of the wavefront at t = t.' Option o3 accurately describes this process.

The NCERT states, 'Now, according to Huygens principle, each point of the wavefront is the source of a secondary disturbance and the wavelets emanating from these points spread out in all directions with the speed of the wave.' Option o2 aligns with this.

The NCERT text mentions, 'The wave theory was not readily accepted primarily because of Newton’s authority and also because light could travel through vacuum and it was felt that a wave would always require a medium to propagate from one point to the other.' Option o3 highlights this key reason.

The NCERT states, 'Huygens argued that the amplitude of the secondary wavelets is maximum in the forward direction and zero in the backward direction; by making this adhoc assumption, Huygens could explain the absence of the backwave.' Option o3 matches this perfectly.

The NCERT states, 'If we have a point source emitting waves uniformly in all directions, then the locus of points which have the same amplitude and vibrate in the same phase are spheres and we have what is known as a spherical wave.' Thus, for a point source, a spherical wave is formed.

The NCERT states, 'At a large distance from the source, a small portion of the sphere can be considered as a plane and we have what is known as a plane wave.' Therefore, at large distances, a spherical wavefront approximates a plane wave.