NEET Wave Optics MCQs & PYQs

Practice NEET Wave Optics Questions

Question 111:

easy

A parallel beam of fast moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statements is correct?

(2013)

The de Broglie wavelength of an electron is $\lambda = \frac{h}{mv}$. As the speed $v$ increases, the wavelength $\lambda$ decreases. The angular width of the central maximum is $2\theta = \frac{2\lambda}{a}$. Since $\lambda$ decreases, the angular width will decrease.

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Question 112:

easy

A parallel beam of monochromatic light of wavelength $5000 \AA$ is incident normally on a single narrow slit of width 0.001 mm. The light is focused by a convex lens on a screen placed in focal plane. The first minimum will be formed for the angle of diffraction equal to

(1993)

For the first minimum in a single slit diffraction pattern, $a \sin\theta = \lambda$. Thus, $\sin\theta = \frac{\lambda}{a} = \frac{5000 \times 10^{-10}}{0.001 \times 10^{-3}} = \frac{5 \times 10^{-7}}{10^{-6}} = 0.5$. Therefore, $\theta = \sin^{-1}(0.5) = 30^\circ$.

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Question 113:

easy

Assume that light of wavelength 600 nm is coming from a star. The limit of resolution of telescope whose objective has a diameter of 2 m is:

(2020)

The limit of resolution of a telescope is given by $\Delta\theta = \frac{1.22 \lambda}{D}$. Substituting the values, $\Delta\theta = \frac{1.22 \times 600 \times 10^{-9}}{2} = 1.22 \times 300 \times 10^{-9} = 3.66 \times 10^{-7} rad$.

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