NEET Wave Optics — Set 8

Question 1

What is the shape of the wavefront produced by a point source in a uniform medium?

Accepted Answer

A point source emits waves uniformly in all directions, producing spherical wavefronts in a medium where the speed is isotropic.

Question 2

In Young’s double-slit experiment, if the slit separation is $ 0.25 \, \text{mm} $, the screen is $ 1.0 \, \text{m} $ away, and the fringe width is $ 2.4 \, \text{mm} $, what is the wavelength of light?

Accepted Answer

Fringe width $ \beta = \frac{\lambda D}{d} $. Given $ \beta = 2.4 \, \text{mm} = 2.4 \times 10^{-3} \, \text{m} $, $ D = 1.0 \, \text{m} $, $ d = 0.25 \, \text{mm} = 2.5 \times 10^{-4} \, \text{m} $. $ \lambda = \frac{\beta d}{D} = \frac{2.4 \times 10^{-3} \times 2.5 \times 10^{-4}}{1.0} = 6.0 \times 10^{-7} \, \text{m} = 600 \, \text{nm} $.

Question 3

What is the intensity of light after passing through two polaroids with pass-axes at $ 30^\circ $, if the initial unpolarized intensity is $ I_0 $?

Accepted Answer

After the first polaroid, $ I = \frac{I_0}{2} $. After the second at $ 30^\circ $, $ I = \frac{I_0}{2} \cos^2 30^\circ = \frac{I_0}{2} \times \frac{3}{4} = \frac{3I_0}{8} $.

NEET Physics: Wave Optics — Practice Set 8

Q1. What is the shape of the wavefront produced by a point source in a uniform medium?

Q2. In Young’s double-slit experiment, if the slit separation is \( 0.25 \, \text{mm} \), the screen is \( 1.0 \, \text{m} \) away, and the fringe width is \( 2.4 \, \text{mm} \), what is the wavelength of light?

Q3. What is the intensity of light after passing through two polaroids with pass-axes at \( 30^\circ \), if the initial unpolarized intensity is \( I_0 \)?

Q4. What is the resultant amplitude of two coherent waves of amplitude \( a \) with a phase difference of \( 3\pi \)?

Q5. What is the resultant amplitude of two coherent waves of amplitude \( a \) with a phase difference of \( 2\pi \)?

Q6. What is the wavelength of light in a medium with refractive index 1.4 if its wavelength in air is \( 560 \, \text{nm} \)?

Q7. What is the wavelength of light in water if its wavelength in air is \( 600 \, \text{nm} \) and the refractive index of water is 1.33?

Q8. What is the distance of the first dark fringe from the central maximum in a double-slit experiment if \( \lambda = 540 \, \text{nm} \), \( d = 0.2 \, \text{mm} \), and \( D = 1.6 \, \text{m} \)?

Q9. In a double-slit experiment, if the screen is moved closer to the slits, what happens to the fringe width?

Q10. What is the condition for the first secondary maximum in a single-slit diffraction pattern?