Optics Objective Questions And Answers

Optics

Each of the following questions comprises two statements. The assertion is expressed by Statement 1 and the reason is expressed by Statement 2.

Each question has four options (1), (2), (3), and (4) as given below, out of which only ONE is correct.

  1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.
  2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.
  3. Statement 1 is true and Statement 2 is false.
  4. Statement 1 is false and Statement 2 is true.
  5. Both Statement 1 and Statement 2 are false.

Some questions are preceded, by a supporting paragraph in addition to the statements.

Optics Objective Questions And Answers

Ray Optics

Question 1. Statement 1 A thick lens shows more chromatic aberration.

Statement 2 A thick lens behaves asifitis composed of many thin lenses.

Answer: 3. Statement 1 is true and Statement 2 is false.

Chromatic aberration is a defect in lenses in not focusing all the colors at the same point. It is caused by dispersion and is prominent with thick lenses. A thick lens is like a combination of truncated prisms and not composed of thin lenses.

Optics Objective Questions

Question 2. Statement 1 A total reflecting prism is used to erect the inverted image without any deviation.

Statement 2 The rays of light incident perpendicular to the base of the prism emerge as parallel rays.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

An erecting prism is a right-angled isosceles prism used to erect an inverted image without any deviation, as shown in the ray diagram.

Optics Objective Questions And Answers Erecting Prism Q2

Question 3. Statement 1 The color of a green flower seen through a red glass appears to be dark.

Statement 2 A red glass transmits only red light.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

The green flower emits green light which is absorbed by the red glass and appears dark. This is true as a red glass emits only red light.

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Question 4. Statement 1 If a convex lens is kept in water, its converging power decreases.

Statement 2 The focal length of a convex lens increases in water.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

Optics Objective Questions

The focal length of a lens depends on the refractive index of the surrounding medium.

When in air, \(\frac{1}{f_{\mathrm{a}}}=\left({ }^{\mathrm{a}} \mu_{\mathrm{g}}-1\right)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)=k\left({ }^{\mathrm{a}} \mu_{\mathrm{g}}-1\right)\)

When in water, \(\frac{1}{f_{\mathrm{w}}}=\left({ }^{\mathrm{w}} \mu_{\mathrm{g}}-1\right) k=k\left(\frac{\mu_{\mathrm{g}}}{\mu_{\mathrm{w}}}-1\right)\)

As \(\frac{\mu_{\mathrm{g}}}{\mu_{\mathrm{w}}}<{ }^{w_{\mathrm{g}}} \mu_{\mathrm{g}}, \frac{1}{f_{\mathrm{a}}}>\frac{1}{f_{\mathrm{w}}}\)

Hence, the converging power is reduced when in water. This is the same as /w>/a.

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Question 5. Statement 1 Diamonds glitter brilliantly.

Statement 2 Diamonds absorb sunlight.

Answer: 3. Statement 1 is true and Statement 2 is false.

The sparkling of a diamond is due to its high refractive power (refractive index = 2.4) and its cut shape. Due to the high refractive index, the critical angle is small and the light inside the diamond gets internally reflected several times before emergence, thus making ‘ the diamond glitter brilliantly. The glitter of a diamond is not due to the absorption of light but due to total internal reflection.

Question 6. Statement 1 Red light is used as the danger signal.

Optics Objective Questions

Statement 2 The velocity of red light is maximum and thus it offers more visibility in the dark.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

Red light has the longest wavelength in the visible region and undergoes the least scattering according to Rayleigh’s law,\(I \propto \frac{1}{\lambda^4}\). Hence, a red signal is visible from a long distance. Scattering spreads the light in a wider area but reduces the intensity. Red light is scattered the least and has the maximum intensity as well.

Question 7. Statement 1 If the optical density of a substance is more than that of water then the mass density of the substance can be less than water.

Statement 2 Optical density and mass density are not related.

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Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

A greater optical density does not always mean a greater mass density (mass per unit volume). For example, kerosene is lighter than water, but it has a higher refractive index, so it is optically denser than water. In most cases though, a greater optical density is associated with a greater mass density.

Question 8. Statement 1 A secondary rainbow has an inverted color sequence, while a primary rainbow does not.

Statement 2 A secondary rainbow is formed by a single total internal reflection.

Answer: 3. Statement 1 is true and Statement 2 is false.

In the formation of a secondary rainbow, light undergoes two internal reflections inside water droplets. The color sequence in a secondary rainbow is thus inverted as compared to that in a primary one.

Question 9. Statement 1 When an object is placed between two plane mirrors kept parallelly, all the images formed are of the same intensity.

Statement 2 In the case of parallel plane mirrors, only two images are possible.

Answer: 5. Both Statement 1 and Statement 2 are false.

When an object is placed between two parallel plane mirrors, an infinite number of images are formed with gradually decreasing intensity due to absorption and multiple reflections.

Optics Objective Questions

Question 10. Statement 1 A single lens produces a coloured image of an object illuminated by white light.

Statement 2 The refractive index of the material of a lens is different for different wavelengths of light.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

A single lens produces a colored image of an object in white light (called chromatic aberration). Different components of white light have different values of focal length and do not get focused at a single position.

Question 11. Statement 1 Endoscopy involves the use of optical fibers to study internal organs.

Statement 2 The working of optical fibers is based on the phenomenon of total internal reflection.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

An endoscope is used to examine internal organs. In the process, optical fibers are used which work on the principle of total internal reflection.

Question 12. Statement 1 A double convex lens (μ = 1.5) has a focal length of 10 cm. When the lens is immersed in water(μ = 4/3), its focal length becomes 39 cm.

Statement 2 \(\frac{1}{f}=\left(\frac{1}{R_1}-\frac{1}{R_2}\right)\left(\frac{\mu_1-\mu_w}{\mu_w}\right)\)

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

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When air, the focal length fa is given by

⇒ \(\frac{1}{f_{\mathrm{a}}}=\frac{1}{10 \mathrm{~cm}}=\left(\mu_1-1\right)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)\)

⇒ \((1.5-1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)\) (1)

When immersed in water, the focal length /w is given

∴ \(\frac{1}{f_{\mathrm{w}}}=\left(\frac{\mu_1}{\mu_{\mathrm{w}}}-1\right)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)=\left(\frac{1.5}{1.33}-1\right)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)\) (2)

Dividing (1) by (2),

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∴ \(\frac{f_{\mathrm{w}}}{10 \mathrm{~cm}}=\frac{0.5}{\frac{1.5}{1.33}-1} \Rightarrow f_{\mathrm{w}}=39.1 \mathrm{~cm}\)

Optics Objective Questions

Question 13. Statement 1 A red-colored object appears dark in yellow light.

Statement 2 Red light is scattered less.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

A red-colored object reflects only red light and absorbs yellow light. The scattering of red light is the least because its wavelength is maximum.

Question 14. Statement 1 By roughening the surface of a glass sheet, its transparency can be reduced.

Statement 2 A rough glass surface absorbs more heat.

Answer: 3. Statement 1 is true and Statement 2 is false.

Roughening a glass surface reduces its transparency because of irregular reflection and not due to absorption.

Question 15. Statement 1 A normal human eye can clearly see all the objects beyond a certain minimum distance.

Statement 2 The human eye has the capacity to suitably adjust the focal length of the eye lens to a certain extent.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

The human eye can adjust its focal length to see objects clearly beyond 25 cm.

Question 16. Statement 1 A microscope forms the magnified image of an object.

Statement 2 The angle subtended by the image is more than that subtended by the object.

Optics Objective Questions

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

A microscope (simple or compound) increases the visual angle of an image so that the final image formed at 25 cm from the eye appears magnified as compared to the object.

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NEET Foundation Class 12 Physics NEET Physics

Question 17. Statement 1 If the objective and eye lenses of a microscope are interchanged then it can work as a telescope.

Statement 2 The objective lens of a telescope has a small focal length.

Answer: 5. Both Statement 1 and Statement 2 are false.

The objective and eye lenses of a microscope cannot be interchanged to convert it into a telescope. This is because a microscope’s lens has a small focal length (around a few cm), whereas a telescope’s objective has a large focal length.

Question 18. Statement 1 Magnification by a convex mirror is always positive, but that by a concave mirror may be either positive or negative.

Statement 2 It depends on the sign convention chosen.

Answer: 3. Statement 1 is true and Statement 2 is false.

In a convex mirror, the image formed is virtual, diminished, and erect (positive magnification).

In a concave mirror, the magnification is positive for an object lying between the focus and the pole (u < f) and negative for u >f when the image formed is real and inverted.

Question 19. Statement 1 Owls can move freely during the night.

Statement 2 They have a large number of rods on their retina.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

Owls have appreciably better night visions because they have comparatively more rods and not as many cones. Thus, they lose color vision but see a lot better at night when it is almost dark. But in total darkness, they can see nothing. They always need some light to see.

Question 20. Statement 1 The formula connecting u, v, and / for a spherical mirror is valid only for those mirrors whose sizes are very small compared to their radii of curvature.

Statement 2 The laws of reflection are strictly valid for plane surfaces but not for large spherical surfaces.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

The relation connecting u, v, and f in ray optics is valid for paraxial rays, and the laws of reflection are true for plane surfaces.

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Question 21. Statement 1 The edge of the image of a white object formed by a concave mirror on the screen appears white.

Statement 2 A concave mirror does not suffer from chromatic aberration.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

The image formed due to a concave mirror does not suffer from chromatic aberrations, so it appears white.

Question 22. Statement 1 A ray of light is incident from outside on a glass sphere surrounded by air. This ray may suffer a total internal reflection at the second interface.

Statement 2 If a ray of light goes from a denser to a rarer medium, it bends away from the normal.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

A ray of light incident on a glass sphere gets refracted and strikes the surface again. It may be totally reflected if the surface angle of incidence is greater than the critical angle.

Question 23. Statement 1 A real image is formed when two rays starting from a point and moving along different paths meet again at some other point.

Statement 2 A real image can never be formed by reflection from a convex mirror or refraction through a concave lens.

Answer: 3. Statement 1 is true and Statement 2 is false.

Real images are formed by the actual intersection of rays after reflection or refraction.

Real images can be formed by a convex mirror or a concave lens, as shown in the following figure.

Optics Objective Questions And Answers Real Image Q30

Question 24. Statement 1 In high-quality optical devices, such as cameras, binoculars, and periscopes, prisms instead of plane mirrors are used to reflect light.

Statement 2 In-plane mirrors, reflections occur both at the front and rear (silvered) surfaces.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

A reflection from a prism is actually a total internal reflection, where there is 100% reflection. This is not true for a plane mirror.

Question 25. Statement 1 The sun rises before the actual sunrise.

Statement 2 During sunrise, refraction takes place through different atmospheric layers.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

The time delay (advanced sunrise and delayed sunset) is due to atmospheric refraction. The sun is visible to us 2 minutes before the actual sunrise and 2 minutes after the actual sunset.

Question 26. Statement 1 Sometimes the rainbow is seen in the sky when it is raining. When one sees a rainbow, one’s back is towards the sun.

Statement 2 Internal reflection from water droplets causes dispersion. The final ray is in the backward direction.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

A rainbow is caused by refraction, dispersion, and total internal reflection of sunrays through water droplets suspended in the atmosphere. Rainbows always appear in the section of the sky directly opposite the sun.

Question 27. Statement 1 The frequencies of the incident reflected and refracted beams of light incident from one medium to another are the same.

Statement 2 The incident, reflected, and refracted rays are coplanar.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

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During reflection and refraction, the frequency of photon (E =hf) does not change because E and B are continuous at the boundary of the two media. The planes of incidence and refraction are actually the same plane

Question 28. Statement 1 The corpuscular theory fails to explain the velocities of light in air and water.

Statement 2 According to the corpuscular theory, light should travel faster in a denser medium than in a rarer medium.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

According to Newton’s corpuscular theory, the speed of light in a denser medium is greater than the speed in a rarer medium, which is • not true.

Question 29. Statement 1 Optical fibers are used for telecommunications.

Statement 2 The optical fibers work on the principle of total internal reflection.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

Optical fibers work on the principle of total internal reflection. They are used in telecommunications because of their higher bandwidths, lower attenuations, and no interference from stray signals.

Question 30. Statement 1 When a beam of white light is passed through a lens, violet light gets more refracted than red light.

Statement 2 The focal length of the red light is greater than that of the violet light.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

White light passing through a lens undergoes dispersion. Violet light is the most refracted and red light is the least refracted because \(\mu_v>\mu_r\). This is why \(f_{\mathrm{v}}<f_{\mathrm{r}}\).

Optics Objective Questions And Answers Ray Optics Q30

Question 31. Statement 1 Goggles (sunglasses) have zero power.

Statement 2 The radius of curvature of both sides of the lens is the same.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

Power depends on the radii of curvature of the curved surfaces of a lens and this is given by

∴ \(P=\frac{1}{f}=(\mu-1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)\)

P = 0 when R1 =R2.

Wave Optics And Electromagnetic Waves

Question 1. Statement 1 In Young’s double-slit experiment (YDSE), bright and dark fringes are equally spaced.

Statement 2 It only depends upon phase differences.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

The separation between two consecutive dark or two consecutive bright fringes is equally spaced. The spacing, known as the fringe width, is given by \(\beta=\frac{D \lambda}{d}\). The position of the minima or maxima depends on the phase difference.

Question 2. Statement 1 A thin film such as a soap bubble or a thin layer of oil on water shows beautiful colors when illuminated by white light.

Statement 2 It happens due to the interference of light reflected from the upper Surface of the thin film.

Answer: 3. Statement 1 is true and Statement 2 is false.

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Colors in a thin film arise due to interference of light waves reflected from the top and bottom surfaces of the thin film. The colors that appear depend upon the thickness of the film and the angle of incidence of the incident white light.

Question 3. Statement 1 The sun looks bigger in size at sunrise and sunset than during the day.

Statement 2 The phenomenon of diffraction bends light rays.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

The appearance of the bigger size of the sun during sunrise or sunset is due to atmospheric refraction. It is not due to diffraction, which is a wave phenomenon of bending of light around the comer.

Question 4. Statement 1 A colored spectrum is seen when we look through a muslin cloth.

Statement 2 It is due to the diffraction of white light passing through fine slits.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

A piece of muslin cloth effectively acts as a series combination of fine slits (like a grating). White rays undergo diffraction and produce a colored spectrum.

Question 5. Statement 1 Clouds in the sky generally appear to be whitish.

Statement 2 Diffractions due to clouds are efficient in equal measures at all wavelengths.

Answer: 3. Statement 1 is true and Statement 2 is false.

Clouds consist of tiny water droplets and dust particles whose sizes are very large compared to the wavelength of light from the sun So, there is the least scattering and we receive unscattered sunlight, which is white.

Question 6. Statement 1 An electron microscope has more resolving power than an optical microscope.

Statement 2 We can control the energy of electrons.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

The resolving power of a microscope is inversely proportional to wavelength. The de Broglie wavelength \(\left(\lambda=\frac{h}{m v}\right)\) of the electron beam used in an electron microscope is much shorter than the wavelength of the visible light used in an optical microscope. Hence, an electron microscope has a greater resolving power. The energy of an electron can be controlled by accelerating the voltage.

Question 7. Statement 1 The resolving power of a telescope is more if the diameter of the objective lens is more.

Statement 2 An objective lens of a larger diameter collects more light.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

The angular position of the first minimum in the diffraction pattern of a circular aperture of diameter D is \(\theta_1=1.22 \frac{\lambda}{D}\)

The reciprocal of θ1 is the measure of resolving power, i.e., \(\frac{D}{1.22 \lambda}\)

With an increase in diameter, the resolving power will increase.

Question 8. Statement 1 The focal length of the objective lens in a telescope is longer than that of the eyepiece.

Statement 2 A telescope has a high resolving power due to the large focal length of its objective.

Answer: 3. Statement 1 is true and Statement 2 is false.

The large focal length of an objective lens produces a high magnification but for a high resolving power, the aperture (diameter) has to be large.

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Question 9. Statement 1 The resolving power of a telescope depends only on the wavelength of the diffracted light.

Statement 2 The resolving power is proportional to the square of the wavelength of the diffracted light.

Answer: 5. Both Statement 1 and Statement 2 are false.

Resolving power is inversely proportional to the wavelength of light used and directly proportional to the aperture (diameter) of the objective lens.

Question 10. Statement 1 The standard optical diffraction gratings cannot be used to discriminate between different X-ray wavelengths.

Statement 2 The grating spacing is not of the order of X-ray wavelengths.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

Diffraction effects are appreciable when the wavelength is of the order of the size of the diffracting element.

The wavelengths of X-rays are much smaller than the spacing of the grating elements, so diffraction is insignificant in discriminating X-ray wavelengths.

Question 11. Statement 1 Two coherent point sources of light S1 and S2 are placed on a line as shown. P and Q are two points on that line. If the maximum intensity is observed at point P then, the maximum intensity should also be observed at Q.

Statement 2 In the figure given with Statement 1, the distance |S1P- S2P| is equal to |S2Q- S1Q|

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

Waves originating from the coherent sources S1 and S2 superpose at P to produce the maximum intensity. This is true when the path difference (S1P- S2P) is nk, where n = 0, 1, 2,…

The same path difference (S2Q- S1Q) is also given for Q, so Q will also be the position of maximum intensity.

Optics Objective Questions And Answers Wave Optics And Electromagnetic Waves Two Coherent Point Q11

Question 12. Statement 1 When a tiny circular obstacle is placed in the path of a beam of light some distance away, a bright spot is seen at the center of the shadow of the obstacle.

Statement 2 A destructive interference occurs at the center of the shadow.

Answer: 3. Statement 1 is true and Statement 2 is false.

A plane wavefront from a distant source incident on a circular obstacle gets diffracted and interferes constructively at the center of the shadow region and forms a bright spot.

Question 13. Statement 1 Radio waves can be polarized.

Statement 2 Sound waves in air are longitudinal in nature.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

Radio waves are electromagnetic (transverse) waves and can be polarized.

Question 14. Statement 1 When a ray of light is incident at a polarizing angle on a glass, the refracted ray is partially polarized.

Statement 2 The intensity of light decreases during polarization.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

When unpolarized light is incident on a transparent medium (glass or water) at a polarizing angle, the reflected light is completely polarized, whereas the refracted ray is partially polarized.

When unpolarized light is polarized at reflection, the energy is partly associated with the reflected and partly with the refracted waves. During transmission through a polaroid, the intensity is reduced according to Malus’s law.

Question 15. Statement 1 Skiers use polarized glasses.

Statement 2 Light reflected by snow is partially polarized.

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Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

Skiers use polarized sunglasses to eliminate the glare from the plane surface office. The reflected light from plane surfaces is polarized and is blocked by the polarized glasses, thus reducing the glare.

Question 16. Statement 1 A famous painting was made not by using brush strokes in the usual manner but rather by putting a myriad of small color dots. In this painting, the color you see at any given area on the painting changes as you move away.

Statement 2 The angular separation of adjacent dots changes with the distance from the painting.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

The angular separation between two closely spaced dots changes with distance. Due to the finite resolving power of the eye, the two dots appear as one and lead to an apparent change in color.

Question 17. Statement 1 At first glance, the top surface of a morpho butterfly’s wings appears blue-green. If the wings move, the color changes.

Statement 2 Different pigments in the wings reflect light at different angles.

Answer: 3. Statement 1 is true and Statement 2 is false.

The wings of a morpho butterfly create colors by causing light waves to diffract and interfere with its wings, which are composed of nano and micro-scale structures.

Question 18. Statement 1 Dipole oscillations produce electromagnetic waves.

Statement 2 Accelerated charge produces electromagnetic waves.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

A dipole oscillation consists of accelerated charge which, according to Maxwell’s theory, radiates electromagnetic waves.

Question 19. Statement 1 The electromagnetic waves are transverse in nature.

Statement 2 Waves of wavelength 10 mm are radio waves and microwaves.

Answer: 3. Statement 1 is true and Statement 2 is false.

Electromagnetic waves constitute oscillating electric and magnetic fields, which are mutually perpendicular as well as perpendicular to the direction of propagation.

Electromagnetic waves of wavelength in the range 1-30 mm lie in the far-infrared region.

Question 20. Statement 1 Electromagnetic radiation exerts pressure.

Statement 2 Electromagnetic waves carry both momentum and energy.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

The radiant energy falling on a surface exerts pressure \(p=\frac{I}{c}\) for 100% absorption and \(p=\frac{2 I}{c}\) for total reflection, where I = intensity of the incident wave and c = speed of light.

Both energy (E = hv) and momentum \(\left(p=\frac{E}{c}\right)\) are associated with electromagnetic waves.

Question 21. Statement 1 When a charged particle moves in a circular path, it produces electromagnetic waves.

Statement 2 A charged particle has an acceleration.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

A charged particle undergoing circular motion is accelerated, which produces electromagnetic waves.

Question 22. Statement 1 Electromagnetic waves are transverse in nature.

Statement 2 The electric and magnetic fields of an electromagnetic wave are mutually perpendicular to each other and also perpendicular to the direction of propagation.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

Electromagnetic waves are transverse in nature because their components — \(\vec{E}\) vector and \(\vec{B}\) vector—are mutually perpendicular and also perpendicular to the direction of propagation.

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Question 23. Statement 1 In electromagnetic waves, electric and magnetic field lines are perpendicular to each other.

Statement 2 Electric and magnetic fields are self-sustaining.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

Electromagnetic waves are transverse waves with \(\vec{E}\)– and \(\vec{B}\)– components undergoing sinusoidal variations along mutually perpendicular directions. These oscillations are self-sustaining.

Question 24. Statement 1 UV radiations cause photodissociation of ozone (O3) into O2 and O, thus causing damage to the stratospheric ozone layer.

Statement 2 An ozone hole results from global warming and climate damage.

Answer: 2. Statement 1 is true; Statement 2 is true; but Statement 2 is not a correct explanation of Statement 1.

When high-energy ultraviolet rays are absorbed by ozone, the ozone molecules are split into ordinary oxygen molecules and free oxygen atoms:

\(\mathrm{O}_3 \stackrel{\mathrm{uv}}{\longrightarrow} \mathrm{O}_2+\mathrm{O}\)

The decline of ozone in the stratosphere (called the ozone hole) results in reduced absorption of ultraviolet radiation from the sun. This is the cause of global warming and climate damage.

Question 25. Statement 1 Microwave communications are preferred to optical communications.

Statement 2 Microwaves provide a large number of channels and bandwidths compared to optical signals.

Answer: 5. Both Statement 1 and Statement 2 are false.

Optical communication systems are preferred to microwave communication systems for the following reasons. An optical communications system has

  1. A wider bandwidth,
  2. A larger capacity,
  3. A lower power consumption and
  4. An immunity from interference.

Question 26. Statement 1 A quasar emits radio waves more than a radio galaxy.

Statement 2 A quasar is a very small size.

Answer: 3. Statement 1 is true and Statement 2 is false.

A quasar (quasi-stellar radio source) is a massive and extremely remote celestial object that emits large amounts of radiant energy, much larger than a radio galaxy. The average size of quasars is around 0.1 x 106 AU, which is about 1.5 light-years.

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Question 27. Statement 1 A pulsar is a source of radio waves that vary in intensity at regular intervals.

Statement 2 A pulsar is a rotating neutron star.

Answer: 1. Statement 1 is true; Statement 2 is true; and Statement 2 is a correct explanation of Statement 1.

A pulsar (pulsating star) is a rotating neutron star that emits radio waves that sweep through the earth and vary in intensity with time.

Question 28. Statement 1 The environmental damage has increased the amount of ozone in the atmosphere.

Statement 2 An increase in ozone increases the amount of ultraviolet radiation on the earth.

Answer: 5. Both Statement 1 and Statement 2 are false.

The ozone layer absorbs harmful ultraviolet radiation from the sun and saves life on Earth.

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