NEET Wave Optics — Set 21

Question 1

What is the distance of the third dark fringe from the central maximum in a double-slit experiment if $ \lambda = 600 \, \text{nm} $, $ d = 0.4 \, \text{mm} $, and $ D = 2.0 \, \text{m} $?

Accepted Answer

Dark fringe position $ x_n = \frac{\left(n + \frac{1}{2}\right) \lambda D}{d} $. For the third dark fringe, $ n = 2 $. $ \lambda = 6.0 \times 10^{-7} \, \text{m} $, $ d = 4.0 \times 10^{-4} \, \text{m} $, $ D = 2.0 \, \text{m} $. $ x_2 = \frac{\left(2 + \frac{1}{2}\right) \times 6.0 \times 10^{-7} \times 2.0}{4.0 \times 10^{-4}} = \frac{2.5 \times 1.2 \times 10^{-6}}{4.0 \times 10^{-4}} = 7.5 \times 10^{-3} \, \text{m} = 7.5 \, \text{mm} $.

Question 2

What is the nature of the wavefront produced by a plane wave after reflection from a concave mirror?

Accepted Answer

A plane wave reflecting off a concave mirror forms a spherical wavefront converging to the focal point.

Question 3

What is the shape of the wavefront reflected by a plane mirror when a spherical wave is incident on it?

Accepted Answer

A spherical wavefront incident on a plane mirror reflects as a spherical wavefront, diverging from the mirror’s virtual focus.

NEET Physics: Wave Optics — Practice Set 21

Q1. What is the distance of the third dark fringe from the central maximum in a double-slit experiment if \( \lambda = 600 \, \text{nm} \), \( d = 0.4 \, \text{mm} \), and \( D = 2.0 \, \text{m} \)?

Q2. What is the nature of the wavefront produced by a plane wave after reflection from a concave mirror?

Q3. What is the shape of the wavefront reflected by a plane mirror when a spherical wave is incident on it?

Q4. What is the path difference for the third dark fringe in a double-slit experiment?

Q5. What is the refractive index of a medium if the speed of light in it is \( 1.8 \times 10^8 \, \text{m/s} \) and in vacuum is \( 3.0 \times 10^8 \, \text{m/s} \)?

Q6. What is the refractive index of a medium if the critical angle for light passing into air is \( 39^\circ \)?

Q7. In a double-slit experiment, if \( \lambda = 400 \, \text{nm} \), \( d = 0.4 \, \text{mm} \), and \( D = 2.0 \, \text{m} \), what is the distance of the third bright fringe from the central maximum?

Q8. What is the condition for the third secondary maximum in a single-slit diffraction pattern?

Q9. What is the wavelength of light in a medium with refractive index 1.5 if its wavelength in vacuum is \( 750 \, \text{nm} \)?

Q10. What is the critical angle for light passing from a medium with refractive index 1.85 to air (refractive index 1.0)?