Assertion (A): In Young’s double slit experiment, if one of the slits is closed, intensity at the position of central fringe becomes half.
Reason (R): Resultant intensity, being sum of intensities from individual slits, becomes half as one slit is closed.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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If intensity from one slit is (I_0), the central maximum with two slits is (4I_0). If one slit is closed, the intensity at the center becomes (I_0), which is one-fourth, not half. Reason (R) is also incorrect as intensities don't simply add algebraically. Both A and R are false.
Assertion (A): In YDSE, fringes with blue light are thicker than those for red light.
Reason (R): In YDSE, the \(n^{\text{th}}\) maxima always comes before the \(n^{\text{th}}\) minima.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Fringe width \(\beta = \frac{\lambda D}{d}\). Since \(\lambda_{\text{blue}} < \lambda_{\text{red}}\), blue fringes are thinner than red fringes, so A is false. Minima and maxima alternate, and the \(n^{\text{th}}\) dark fringe typically occurs closer to the central maximum than the \(n^{\text{th}}\) bright fringe (for (n ge 1)). So R is also false.
Assertion (A): Light is a wave phenomenon.
Reason (R): Light requires a material medium for its propagation.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Light is an electromagnetic wave and can travel through vacuum, so it does not require a material medium for propagation. Thus, Assertion (A) is true but Reason (R) is false.
Assertion (A): The best contrast of the interference pattern is obtained when the intensity of the emerging lights from the two slits of the Young’s experimental set-up are equal.
Reason (R): Intensity is proportional to the square of the amplitude.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true, as equal intensities (\(I_1 = I_2\)) ensure \(I_{text{min}} = 0\) for maximum contrast.
Reason (R) is true, as intensity \(I propto A^2\). However, (R) does not explain why \(I_1 = I_2\) leads to best contrast.
Assertion (A): The central fringe is bright or dark, it dependents on the initial phase difference between the two coherent sources.
Reason (R): The pattern and position of fringes always remains same even after the introduction of transparent medium in a path of one of the slit.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true. The nature of the central fringe depends on the initial phase difference. Reason (R) is false. Introducing a transparent medium causes a path difference \((n-1)t\) and shifts the entire fringe pattern.
Assertion (A): Diffraction is a sure indication of wave nature.
Reason (R): Only transverse waves can be diffracted.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true; diffraction is a characteristic property of all waves. Reason (R) is false; both transverse (e.g., light) and longitudinal (e.g., sound) waves can be diffracted.
Assertion (A): We cannot get diffraction pattern from a wide slit illuminated by monochromatic light.
Reason (R): In diffraction pattern, all the bright bands are not of the same intensity.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true in a practical sense; a very wide slit (\(a \gg lambda\)) yields a pattern with very small angular spread, making it indiscernible. Reason (R) is true; the intensity of secondary maxima decreases rapidly. (R) does not explain (A).
Assertion (A): Diffraction of light is due to dispersion.
Reason (R): Change in path of light around “the corners separates the wavelength of various colours.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is false; diffraction is the bending of waves, while dispersion is wavelength-dependent refractive index. Reason (R) is false; color separation in diffraction is due to \(\theta \propto \lambda\), not dispersion around corners.
Assertion (A): Sound waves in air cannot be polarised.
Reason (R): Polarisation is the characteristic of light wave only.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
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Assertion (A) is true; sound waves in air are longitudinal waves and cannot be polarized. Reason (R) is false; polarization is a property of all transverse waves, not exclusively light waves.
Assertion (A): Two polaroids are crossed to each other. When either of them is rotated through \(30^\circ\), then only one eighth of the incident unpolarised light passes through the combination.
Reason (R): According to Malus’s law, \(I \propto cos^2 \theta\) where \(I\) is the resultant intensity transmitted and \(\theta\) is the angle between the optical axis of analyser and polariser.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true. Unpolarised light becomes \(I_0/2\) after the first polaroid. With \(60^\circ\) angle between axes, Malus's law gives \(I = (I_0/2)cos^2(60^\circ) = (I_0/2)(1/4) = I_0/8\). Reason (R) correctly states Malus's law, which explains (A).