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Physics > Ray Optics and Optical Instruments > Flashcards

Ray Optics and Optical Instruments Flashcards

1
Q

What is the range of wavelengths for electromagnetic radiation that is detected by the human eye?

A

The range of wavelengths for electromagnetic radiation detected by the human eye is approximately 400 nm to 750 nm.

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2
Q

What is light, according to the text?

A

Light is electromagnetic radiation within the wavelength range of approximately 400 nm to 750 nm.

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3
Q

What two intuitive observations about light are mentioned in the text?

A

The two intuitive observations about light mentioned are its enormous speed and its tendency to travel in straight lines.

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4
Q

What is the speed of light in a vacuum, and what is its commonly accepted value?

A

The speed of light in a vacuum is approximately 2.99792458×10^8m/s, commonly rounded to 3×10^8m/s.

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5
Q

How is the notion of light traveling in straight lines reconciled with its nature as an electromagnetic wave?

A

The wavelength of light is significantly smaller than the size of ordinary objects, allowing light to be considered as traveling in straight lines between points, forming rays of light.

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6
Q

What is a bundle of rays of light called?

A

A bundle of rays of light is called a beam of light.

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7
Q

What phenomena of light are considered in this chapter?

A

Reflection, refraction, and dispersion of light are considered in this chapter.

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8
Q

What basic laws are used to study reflection and refraction of light?

A

The basic laws of reflection and refraction are used to study these phenomena.

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9
Q

What optical instruments are described in this chapter?

A

The construction and working of some important optical instruments, including the human eye, are described in this chapter.

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10
Q

What are the laws of reflection?

A

The angle of reflection equals the angle of incidence, and the incident ray, reflected ray, and the normal to the reflecting surface lie in the same plane.

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11
Q

What surfaces are discussed in relation to the laws of reflection?

A

Curved surfaces, specifically spherical surfaces, are considered

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12
Q

How is the normal defined for curved surfaces?

A

The normal is taken as normal to the tangent to the surface at the point of incidence, along the radius from the center of curvature to the point of incidence.

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13
Q

What is the principal axis, and how is it defined for spherical mirrors?

A

The line joining the pole and the center of curvature of a spherical mirror is known as the principal axis.

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14
Q

What sign convention is adopted for measuring distances in optics?

A

Distances are measured from the pole of the mirror or the optical center of the lens. Positive distances are in the direction of incident light, while negative distances are in the opposite direction.

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15
Q

What is the geometric center of a spherical mirror called?

A

The pole.

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16
Q

What is the principal focus of a concave mirror?

A

The point where parallel rays converge after reflection.

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17
Q

How is the focal length of a mirror related to its radius of curvature?

A

The focal length (f) equals half the radius of curvature (R/2).

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18
Q

Describe the geometry of reflection for an incident ray parallel to the principal axis.

A

For an incident ray parallel to the principal axis, the reflected ray passes through the focal point, and the angle of reflection is twice the angle of incidence.

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19
Q

What is the focal plane of a mirror?

A

The plane through the principal focus normal to the principal axis, where rays converge or appear to diverge after reflection.

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20
Q

What is the definition of an image in optics?

A

An image is formed when rays emanating from a point on an object actually meet at another point after reflection and/or refraction.

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21
Q

How do we differentiate between real and virtual images?

A

A real image is formed when rays actually converge to a point, while a virtual image is formed when rays do not actually meet but appear to diverge from a point when produced backwards.

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22
Q

How is point-to-point correspondence between an object and its image established?

A

Point-to-point correspondence between an object and its image is established through reflection and/or refraction.

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23
Q

What is the principle behind constructing ray diagrams for image formation?

A

Ray diagrams are constructed by tracing the paths of any two rays emanating from a point on an object and finding their point of intersection after reflection at a spherical mirror.

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24
Q

What are the four convenient rays chosen for constructing ray diagrams in practice?

A

(i) A ray parallel to the principal axis, reflecting through the focus.
(ii) A ray passing through the center of curvature, reflecting back along the same path.
(iii) A ray passing through (or directed towards) the focus, reflecting parallel to the principal axis.
(iv) A ray incident at any angle at the pole, following the laws of reflection.

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25
Q

How is the mirror equation derived using similarity of triangles?

A

The mirror equation is derived by considering similar triangles formed by the object, image, and focal point.

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26
Q

What is the mirror equation?

A

The mirror equation relates the object distance (u), image distance (v), and focal length (f) of a spherical mirror, expressed as 1/v + 1/u = 1/f.

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27
Q

What is linear magnification?

A

Linear magnification (m) is the ratio of the height of the image (h¢) to the height of the object (h), expressed as m = -v/u.

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28
Q

Are the mirror equation and magnification formula valid for all cases of reflection by a spherical mirror?

A

Yes, with the proper use of sign convention, the mirror equation and magnification formula are valid for all cases of reflection by a spherical mirror, whether the image formed is real or virtual.

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29
Q

What happens when a beam of light encounters another transparent medium?

A

A part of the light gets reflected back into the first medium while the rest enters the other medium.

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30
Q

What is the phenomenon called when the direction of propagation of an obliquely incident ray of light changes at the interface of two media?

A

Refraction of light.

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31
Q

What are the laws of refraction according to Snell’s experiments?

A

(i) The incident ray, the refracted ray, and the normal to the interface at the point of incidence all lie in the same plane.
(ii) The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant.

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32
Q

What is the mathematical representation of Snell’s law of refraction?

A

sin i/sin r = n21, where n21 is the refractive index of the second medium with respect to the first medium.

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33
Q

How does the refracted ray behave relative to the incident ray when n21>1?

A

The refracted ray bends towards the normal.

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34
Q

How does the refracted ray behave relative to the incident ray when n21 <1?

A

The refracted ray bends away from the normal.

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35
Q

What is optical density, and how does it relate to refractive index?

A

Optical density is the ratio of the speed of light in two media. It should not be confused with mass density. Optical density is higher in optically denser media, even if their mass density is lower.

36
Q

What is the relationship between the refractive indices of two media, n12 and n21?

A

n12 = 1/n21

37
Q

How can the refractive index of a third medium with respect to the first two be calculated?

A

n32 = n31×n12, where n31 is the refractive index of medium 3 with respect to medium 1.

38
Q

What happens to a beam of light passing through a rectangular slab?

A

The emergent ray is parallel to the incident ray, suffering lateral displacement, but no deviation.

39
Q

What happens to the apparent depth of an object submerged in water when viewed near the normal direction?

A

The apparent depth (ℎ1) is less than the real depth (ℎ2) and is calculated by dividing the real depth by the refractive index of the medium (water).

40
Q

What happens when light travels from an optically denser medium to a rarer medium at the interface?

A

It is partly reflected back into the same medium and partly refracted to the second medium, known as internal reflection.

41
Q

How does the angle of incidence affect the angle of refraction when light enters from a denser medium to a rarer medium?

A

The angle of refraction increases with the angle of incidence until it reaches a critical angle where total internal reflection occurs.

42
Q

What is the critical angle?

A

It is the angle of incidence corresponding to an angle of refraction of 90°, where total internal reflection occurs.

43
Q

How is the critical angle related to Snell’s law?

A

The critical angle is determined by Snell’s law and the refractive indices of the two media, where the refractive index of the denser medium with respect to the rarer medium is equal to 1/sin(critical angle).

44
Q

Describe a demonstration of total internal reflection.

A

Total internal reflection can be demonstrated using a laser pointer directed obliquely at the surface of water in a beaker, observing when the angle of refraction is totally absent and the beam is totally reflected back into the water.

45
Q

What are some applications of total internal reflection?

A

Prisms, used for bending light and inverting images, and optical fibers, extensively used for transmitting audio and video signals over long distances, utilize total internal reflection.

46
Q

How do optical fibers work?

A

Optical fibers guide light through total internal reflection, maintaining the intensity of the light signal over long distances, and are used in various applications including telecommunications and medical imaging.

47
Q

What are the main characteristics of optical fibers?

A

Optical fibers are made of high-quality composite glass/quartz fibers with a core and cladding, ensuring minimal loss of light intensity over long distances and flexibility to transmit light even when bent.

48
Q

What are some uses of optical fibers?

A

Optical fibers are used for transmitting audio and video signals, facilitating medical imaging, and in decorative lamps, demonstrating their versatility in various applications.

49
Q

What is refraction at a spherical interface, and how is it approached?

A

Refraction at a spherical interface between two transparent media is considered by treating an infinitesimal part of the spherical surface as planar. The laws of refraction are applied at every point on the surface, with the normal at the point of incidence perpendicular to the tangent plane to the spherical surface at that point, passing through its centre of curvature.

50
Q

How are thin lenses defined, and what is essential for their formation?

A

A thin lens is a transparent optical medium bounded by two surfaces, at least one of which should be spherical. For the formation of images by thin lenses, the lens maker’s formula and lens formula are derived, considering successive refractions at the two surfaces of the lens.

51
Q

Explain the geometry of image formation by a single spherical surface.

A

The geometry involves the formation of an image I of an object O on the principal axis of a spherical surface with the centre of curvature C and radius of curvature R. Rays incident from a medium of refractive index n1 to another of refractive index n2 are considered, applying Snell’s law and the small angle approximation.

52
Q

What are the equations derived for refraction by a single spherical surface?

A

The equations derived are:
n1/u + n2/v = n2-n1/R (Lens Maker’s Formula)
1/f = n2-n1/n1 (1/R1 − 1/R2) (Lens Formula)

53
Q

How is the image formation by a double convex lens explained?

A

Image formation involves two steps: the first refracting surface forms the image of the object, which acts as a virtual object for the second surface that forms the final image. Equations are derived for each interface to determine the image position and characteristics.

54
Q

Define the lens maker’s formula and its significance.

A

The lens maker’s formula, 1/f = (n-1) (1/R1-1/R2), relates the focal length of a lens to its refractive index and the radii of curvature of its surfaces. It is essential for designing lenses of desired focal length using surfaces of suitable radii of curvature.

55
Q

What is the thin lens formula, and under what conditions is it applicable?

A

The thin lens formula, 1/f = 1/v-1/u, relates the object distance (u), image distance (v), and focal length (f) of a lens. It is valid for both convex and concave lenses, as well as for real and virtual images, under the thin lens approximation.

56
Q

How is magnification defined for a lens, and what are its characteristics?

A

Magnification (m) is defined as the ratio of the size of the image to that of the object, m = h’/h = v/u. For a lens, m is positive for erect (and virtual) images and negative for inverted (and real) images.

57
Q

What is the power of a lens, and how is it calculated?

A

The power (P) of a lens is the measure of the convergence or divergence it introduces in light falling on it. It is calculated as P = 1/f, where f is the focal length of the lens. The SI unit for power is dioptre (D), where 1D = 1m^(-1).

58
Q

Explain the combination of thin lenses and the formula for effective focal length.

A

When thin lenses are in contact, their effective focal length is calculated using the formula 1/f = 1/f1 + 1/f2 + 1/f3 + …. The power of the lens combination is the algebraic sum of individual powers, and the magnification of the combination is the product of individual magnifications.

59
Q

What are the angles denoted as i, r₁, r₂, and e in the context of light passing through a prism?

A

The angle denoted as i is the angle of incidence at the first face, r₁ is the angle of refraction at the first face, r₂ is the angle of incidence at the second face, and e is the angle of refraction or emergence.

60
Q

What are the properties of the angles at vertices Q and R in the quadrilateral AQNR?

A

At vertices Q and R of quadrilateral AQNR, two of the angles are right angles.

61
Q

What is the relationship between the angles A, QNR, r₁, and r₂?

A

The relationship is given by the equation: r₁ + r₂ + ÐQNR = 180°.

62
Q

What is the relationship between r₁, r₂, and the angle A?

A

The relationship is given by the equation: r₁ + r₂ = A.

63
Q

How is the total deviation (d) calculated in the prism?

A

The total deviation (d) is calculated as the sum of deviations at the two faces, expressed as: d = (i – r₁) + (e – r₂).

64
Q

What is the physical significance of the symmetry observed between i and e?

A

The symmetry between i and e implies that any given value of d, except for i = e, corresponds to two values of i and hence of e.

65
Q

What is the condition for minimum deviation (Dm) in the prism?

A

The condition for minimum deviation (Dm) is when the refracted ray inside the prism becomes parallel to its base, corresponding to d = Dm and i = e, implying r₁ = r₂.

66
Q

What equations give the relationship between the angles A, r, and Dm?

A

The equations are: 2r = A and Dm = 2i – A or i = (A + Dm)/2.

67
Q

How is the refractive index (n) of the prism determined experimentally?

A

The refractive index (n) of the prism is determined experimentally using the equation: n = sin((A + Dm)/2) / sin(A/2).

68
Q

What is the relationship between the refractive index (n) and the angles A and Dm for thin prisms?

A

For thin prisms, the relationship is approximately given by: Dm ≈ (n² - 1)A.

69
Q

What are some examples of optical devices and instruments mentioned in the chapter?

A

Periscope, kaleidoscope, binoculars, telescopes, microscopes.

70
Q

Describe the principle of a simple magnifier or microscope.

A

A simple magnifier or microscope is a converging lens of small focal length. It is held near the object, one focal length away or less, and the eye is positioned close to the lens on the other side.

71
Q

What is the condition for viewing the image comfortably in a simple microscope?

A

The image should be at a distance of 25 cm or more from the lens.

72
Q

What is the linear magnification m for the image formed at the near point D by a simple microscope?

A

m = D/f +1, ehre D is the near point distance and f is the focal length of the lens.

73
Q

What is the magnification achieved when the image is at infinity in a simple microscope?

A

m = D/f

74
Q

What is the purpose of a compound microscope?

A

A compound microscope uses two lenses, an objective and an eyepiece, to achieve larger magnification than a simple microscope.

75
Q

How is the magnification of a compound microscope calculated?

A

The total magnification is the product of the magnifications due to the objective and the eyepiece: m = L/fo.fe, where L is the tube length, fo is the focal length of the objective, and fe is the focal length of the eyepiece.

76
Q

What are the main considerations with an astronomical telescope?

A

The main considerations are light-gathering power and resolution.

77
Q

Why do modern telescopes use a concave mirror instead of a lens for the objective?

A

Modern telescopes use a concave mirror instead of a lens for the objective because there is no chromatic aberration in a mirror, mechanical support is much less of a problem since a mirror weighs much less than a lens of equivalent optical quality, and a mirror can be supported over its entire back surface, not just over its rim.

78
Q

What are telescopes with mirror objectives called?

A

Telescopes with mirror objectives are called reflecting telescopes.

79
Q

What is one problem with reflecting telescopes?

A

One problem with reflecting telescopes is that the objective mirror focuses light inside the telescope tube, requiring an eyepiece and observer to be near the focal point, obstructing some light.

80
Q

How is the problem of light being focused inside the telescope tube addressed?

A

The problem of light being focused inside the telescope tube can be addressed by either having the observer near the focal point (as in the case of the 200-inch Mt. Palomar telescope), or by deflecting the light with another mirror.

81
Q

What is the arrangement that uses a secondary mirror to deflect the incident light?

A

The arrangement that uses a secondary mirror to deflect the incident light is known as a Cassegrain telescope.

82
Q

Who invented the Cassegrain telescope?

A

The Cassegrain telescope was invented by Cassegrain.

83
Q

What advantage does a Cassegrain telescope offer?

A

A Cassegrain telescope offers the advantage of a large focal length in a short telescope.

84
Q

What is the largest reflecting telescope in India?

A

The largest reflecting telescope in India is located in Kavalur, Tamil Nadu, and it is a 2.34-meter diameter Cassegrain reflecting telescope.

85
Q

Where are the largest reflecting telescopes in the world located and what is their diameter?

A

The largest reflecting telescopes in the world are located in Hawaii, USA, and they are the pair of Keck telescopes with a reflector diameter of 10 meters.

Physics (10 decks)

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