NEET Wave Optics — Set 4

Question 1

What is the angular width of the central maximum in a single-slit diffraction pattern if the slit width is $ 3.0 \, \mu\text{m} $ and the wavelength is $ 450 \, \text{nm} $?

Accepted Answer

Angular width $ 2\theta = \frac{2\lambda}{a} $. $ \lambda = 4.5 \times 10^{-7} \, \text{m} $, $ a = 3.0 \times 10^{-6} \, \text{m} $. $ \sin \theta = \frac{\lambda}{a} = \frac{4.5 \times 10^{-7}}{3.0 \times 10^{-6}} = 0.15 $, $ \theta = \sin^{-1}(0.15) \approx 8.6^\circ $, $ 2\theta \approx 17.2^\circ $.

Question 2

What is the shape of the wavefront emitted by a point source in a uniform medium close to the source?

Accepted Answer

A point source in a uniform medium emits spherical wavefronts, especially close to the source.

Question 3

Why does the intensity of light transmitted through two polaroids drop to zero when their pass-axes are perpendicular?

Accepted Answer

When pass-axes are perpendicular, the electric field component along the second polaroid’s axis is zero (cos 90° = 0), blocking all light per Malus’ law.

NEET Physics: Wave Optics — Practice Set 4

Q1. What is the angular width of the central maximum in a single-slit diffraction pattern if the slit width is \( 3.0 \, \mu\text{m} \) and the wavelength is \( 450 \, \text{nm} \)?

Q2. What is the shape of the wavefront emitted by a point source in a uniform medium close to the source?

Q3. Why does the intensity of light transmitted through two polaroids drop to zero when their pass-axes are perpendicular?

Q4. What is the resultant amplitude of two coherent waves of amplitude \( a \) with a phase difference of \( 6\pi \)?

Q5. Why does the intensity of transmitted light through a polaroid decrease when rotated, even if the incident light is unpolarized?

Q6. What is the angular position of the third minimum in a single-slit diffraction pattern if the slit width is \( 6.0 \, \mu\text{m} \) and the wavelength is \( 480 \, \text{nm} \)?

Q7. In a single-slit diffraction pattern, what happens to the central maximum’s width if the wavelength is quadrupled?

Q8. What happens to the intensity of light when it passes through a polaroid and the polaroid is rotated by \( 90^\circ \) from its initial position?

Q9. Why does the wave theory require light to propagate as transverse waves to explain polarization?

Q10. What is the shape of the wavefront after a plane wave passes through a thin prism?

Q11. Why does the intensity of light remain unchanged in terms of energy when it undergoes interference or diffraction?

Q12. What is the refractive index of a medium if the critical angle for light passing into air is \( 36.9^\circ \)?

Q13. In a double-slit experiment, if the intensity at the central maximum is \( 4I_0 \), what is the intensity where the path difference is \( \lambda/4 \)?

Q14. In a double-slit experiment, if the slit separation is doubled, what happens to the fringe width?