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9
339-342
A bundle of optical fibres can be put to several uses Optical fibres are extensively used for transmitting and receiving FIGURE 9 12 Observing total internal reflection in water with a laser beam (refraction due to glass of beaker neglected being very thin) FIGURE 9
9
340-343
Optical fibres are extensively used for transmitting and receiving FIGURE 9 12 Observing total internal reflection in water with a laser beam (refraction due to glass of beaker neglected being very thin) FIGURE 9 13 Prisms designed to bend rays by 90° and 180° or to invert image without changing its size make use of total internal reflection
9
341-344
12 Observing total internal reflection in water with a laser beam (refraction due to glass of beaker neglected being very thin) FIGURE 9 13 Prisms designed to bend rays by 90° and 180° or to invert image without changing its size make use of total internal reflection Rationalised 2023-24 Physics 232 electrical signals which are converted to light by suitable transducers
9
342-345
FIGURE 9 13 Prisms designed to bend rays by 90° and 180° or to invert image without changing its size make use of total internal reflection Rationalised 2023-24 Physics 232 electrical signals which are converted to light by suitable transducers Obviously, optical fibres can also be used for transmission of optical signals
9
343-346
13 Prisms designed to bend rays by 90° and 180° or to invert image without changing its size make use of total internal reflection Rationalised 2023-24 Physics 232 electrical signals which are converted to light by suitable transducers Obviously, optical fibres can also be used for transmission of optical signals For example, these are used as a ‘light pipe’ to facilitate visual examination of internal organs like esophagus, stomach and intestines
9
344-347
Rationalised 2023-24 Physics 232 electrical signals which are converted to light by suitable transducers Obviously, optical fibres can also be used for transmission of optical signals For example, these are used as a ‘light pipe’ to facilitate visual examination of internal organs like esophagus, stomach and intestines You might have seen a commonly available decorative lamp with fine plastic fibres with their free ends forming a fountain like structure
9
345-348
Obviously, optical fibres can also be used for transmission of optical signals For example, these are used as a ‘light pipe’ to facilitate visual examination of internal organs like esophagus, stomach and intestines You might have seen a commonly available decorative lamp with fine plastic fibres with their free ends forming a fountain like structure The other end of the fibres is fixed over an electric lamp
9
346-349
For example, these are used as a ‘light pipe’ to facilitate visual examination of internal organs like esophagus, stomach and intestines You might have seen a commonly available decorative lamp with fine plastic fibres with their free ends forming a fountain like structure The other end of the fibres is fixed over an electric lamp When the lamp is switched on, the light travels from the bottom of each fibre and appears at the tip of its free end as a dot of light
9
347-350
You might have seen a commonly available decorative lamp with fine plastic fibres with their free ends forming a fountain like structure The other end of the fibres is fixed over an electric lamp When the lamp is switched on, the light travels from the bottom of each fibre and appears at the tip of its free end as a dot of light The fibres in such decorative lamps are optical fibres
9
348-351
The other end of the fibres is fixed over an electric lamp When the lamp is switched on, the light travels from the bottom of each fibre and appears at the tip of its free end as a dot of light The fibres in such decorative lamps are optical fibres The main requirement in fabricating optical fibres is that there should be very little absorption of light as it travels for long distances inside them
9
349-352
When the lamp is switched on, the light travels from the bottom of each fibre and appears at the tip of its free end as a dot of light The fibres in such decorative lamps are optical fibres The main requirement in fabricating optical fibres is that there should be very little absorption of light as it travels for long distances inside them This has been achieved by purification and special preparation of materials such as quartz
9
350-353
The fibres in such decorative lamps are optical fibres The main requirement in fabricating optical fibres is that there should be very little absorption of light as it travels for long distances inside them This has been achieved by purification and special preparation of materials such as quartz In silica glass fibres, it is possible to transmit more than 95% of the light over a fibre length of 1 km
9
351-354
The main requirement in fabricating optical fibres is that there should be very little absorption of light as it travels for long distances inside them This has been achieved by purification and special preparation of materials such as quartz In silica glass fibres, it is possible to transmit more than 95% of the light over a fibre length of 1 km (Compare with what you expect for a block of ordinary window glass 1 km thick
9
352-355
This has been achieved by purification and special preparation of materials such as quartz In silica glass fibres, it is possible to transmit more than 95% of the light over a fibre length of 1 km (Compare with what you expect for a block of ordinary window glass 1 km thick ) 9
9
353-356
In silica glass fibres, it is possible to transmit more than 95% of the light over a fibre length of 1 km (Compare with what you expect for a block of ordinary window glass 1 km thick ) 9 5 REFRACTION AT SPHERICAL SURFACES AND BY LENSES We have so far considered refraction at a plane interface
9
354-357
(Compare with what you expect for a block of ordinary window glass 1 km thick ) 9 5 REFRACTION AT SPHERICAL SURFACES AND BY LENSES We have so far considered refraction at a plane interface We shall now consider refraction at a spherical interface between two transparent media
9
355-358
) 9 5 REFRACTION AT SPHERICAL SURFACES AND BY LENSES We have so far considered refraction at a plane interface We shall now consider refraction at a spherical interface between two transparent media An infinitesimal part of a spherical surface can be regarded as planar and the same laws of refraction can be applied at every point on the surface
9
356-359
5 REFRACTION AT SPHERICAL SURFACES AND BY LENSES We have so far considered refraction at a plane interface We shall now consider refraction at a spherical interface between two transparent media An infinitesimal part of a spherical surface can be regarded as planar and the same laws of refraction can be applied at every point on the surface Just as for reflection by a spherical mirror, the normal at the point of incidence is perpendicular to the tangent plane to the spherical surface at that point and, therefore, passes through its centre of curvature
9
357-360
We shall now consider refraction at a spherical interface between two transparent media An infinitesimal part of a spherical surface can be regarded as planar and the same laws of refraction can be applied at every point on the surface Just as for reflection by a spherical mirror, the normal at the point of incidence is perpendicular to the tangent plane to the spherical surface at that point and, therefore, passes through its centre of curvature We first consider refraction by a single spherical surface and follow it by thin lenses
9
358-361
An infinitesimal part of a spherical surface can be regarded as planar and the same laws of refraction can be applied at every point on the surface Just as for reflection by a spherical mirror, the normal at the point of incidence is perpendicular to the tangent plane to the spherical surface at that point and, therefore, passes through its centre of curvature We first consider refraction by a single spherical surface and follow it by thin lenses A thin lens is a transparent optical medium bounded by two surfaces; at least one of which should be spherical
9
359-362
Just as for reflection by a spherical mirror, the normal at the point of incidence is perpendicular to the tangent plane to the spherical surface at that point and, therefore, passes through its centre of curvature We first consider refraction by a single spherical surface and follow it by thin lenses A thin lens is a transparent optical medium bounded by two surfaces; at least one of which should be spherical Applying the formula for image formation by a single spherical surface successively at the two surfaces of a lens, we shall obtain the lens maker’s formula and then the lens formula
9
360-363
We first consider refraction by a single spherical surface and follow it by thin lenses A thin lens is a transparent optical medium bounded by two surfaces; at least one of which should be spherical Applying the formula for image formation by a single spherical surface successively at the two surfaces of a lens, we shall obtain the lens maker’s formula and then the lens formula 9
9
361-364
A thin lens is a transparent optical medium bounded by two surfaces; at least one of which should be spherical Applying the formula for image formation by a single spherical surface successively at the two surfaces of a lens, we shall obtain the lens maker’s formula and then the lens formula 9 5
9
362-365
Applying the formula for image formation by a single spherical surface successively at the two surfaces of a lens, we shall obtain the lens maker’s formula and then the lens formula 9 5 1 Refraction at a spherical surface Figure 9
9
363-366
9 5 1 Refraction at a spherical surface Figure 9 15 shows the geometry of formation of image I of an object O on the principal axis of a spherical surface with centre of curvature C, and radius of curvature R
9
364-367
5 1 Refraction at a spherical surface Figure 9 15 shows the geometry of formation of image I of an object O on the principal axis of a spherical surface with centre of curvature C, and radius of curvature R The rays are incident from a medium of refractive index n1, to another of refractive index n 2
9
365-368
1 Refraction at a spherical surface Figure 9 15 shows the geometry of formation of image I of an object O on the principal axis of a spherical surface with centre of curvature C, and radius of curvature R The rays are incident from a medium of refractive index n1, to another of refractive index n 2 As before, we take the aperture (or the lateral size) of the surface to be small compared to other distances involved, so that small angle approximation can be made
9
366-369
15 shows the geometry of formation of image I of an object O on the principal axis of a spherical surface with centre of curvature C, and radius of curvature R The rays are incident from a medium of refractive index n1, to another of refractive index n 2 As before, we take the aperture (or the lateral size) of the surface to be small compared to other distances involved, so that small angle approximation can be made In particular, NM will be taken to be nearly equal to the length of the perpendicular from the point N on the principal axis
9
367-370
The rays are incident from a medium of refractive index n1, to another of refractive index n 2 As before, we take the aperture (or the lateral size) of the surface to be small compared to other distances involved, so that small angle approximation can be made In particular, NM will be taken to be nearly equal to the length of the perpendicular from the point N on the principal axis We have, for small angles, tan ÐNOM = MN OM FIGURE 9
9
368-371
As before, we take the aperture (or the lateral size) of the surface to be small compared to other distances involved, so that small angle approximation can be made In particular, NM will be taken to be nearly equal to the length of the perpendicular from the point N on the principal axis We have, for small angles, tan ÐNOM = MN OM FIGURE 9 14 Light undergoes successive total internal reflections as it moves through an optical fibre
9
369-372
In particular, NM will be taken to be nearly equal to the length of the perpendicular from the point N on the principal axis We have, for small angles, tan ÐNOM = MN OM FIGURE 9 14 Light undergoes successive total internal reflections as it moves through an optical fibre Rationalised 2023-24 Ray Optics and Optical Instruments 233 EXAMPLE 9
9
370-373
We have, for small angles, tan ÐNOM = MN OM FIGURE 9 14 Light undergoes successive total internal reflections as it moves through an optical fibre Rationalised 2023-24 Ray Optics and Optical Instruments 233 EXAMPLE 9 5 tan ÐNCM = MN MC tan ÐNIM = MN MI Now, for DNOC, i is the exterior angle
9
371-374
14 Light undergoes successive total internal reflections as it moves through an optical fibre Rationalised 2023-24 Ray Optics and Optical Instruments 233 EXAMPLE 9 5 tan ÐNCM = MN MC tan ÐNIM = MN MI Now, for DNOC, i is the exterior angle Therefore, i = ÐNOM + ÐNCM i = MN MN OM +MC (9
9
372-375
Rationalised 2023-24 Ray Optics and Optical Instruments 233 EXAMPLE 9 5 tan ÐNCM = MN MC tan ÐNIM = MN MI Now, for DNOC, i is the exterior angle Therefore, i = ÐNOM + ÐNCM i = MN MN OM +MC (9 13) Similarly, r = ÐNCM – ÐNIM i
9
373-376
5 tan ÐNCM = MN MC tan ÐNIM = MN MI Now, for DNOC, i is the exterior angle Therefore, i = ÐNOM + ÐNCM i = MN MN OM +MC (9 13) Similarly, r = ÐNCM – ÐNIM i e
9
374-377
Therefore, i = ÐNOM + ÐNCM i = MN MN OM +MC (9 13) Similarly, r = ÐNCM – ÐNIM i e , r = MN MN MC MI − (9
9
375-378
13) Similarly, r = ÐNCM – ÐNIM i e , r = MN MN MC MI − (9 14) Now, by Snell’s law n1 sin i = n 2 sin r or for small angles n1i = n 2r Substituting i and r from Eqs
9
376-379
e , r = MN MN MC MI − (9 14) Now, by Snell’s law n1 sin i = n 2 sin r or for small angles n1i = n 2r Substituting i and r from Eqs (9
9
377-380
, r = MN MN MC MI − (9 14) Now, by Snell’s law n1 sin i = n 2 sin r or for small angles n1i = n 2r Substituting i and r from Eqs (9 13) and (9
9
378-381
14) Now, by Snell’s law n1 sin i = n 2 sin r or for small angles n1i = n 2r Substituting i and r from Eqs (9 13) and (9 14), we get 1 2 2 1 OM MI MC n n n n − + = (9
9
379-382
(9 13) and (9 14), we get 1 2 2 1 OM MI MC n n n n − + = (9 15) Here, OM, MI and MC represent magnitudes of distances
9
380-383
13) and (9 14), we get 1 2 2 1 OM MI MC n n n n − + = (9 15) Here, OM, MI and MC represent magnitudes of distances Applying the Cartesian sign convention, OM = –u, MI = +v, MC = +R Substituting these in Eq
9
381-384
14), we get 1 2 2 1 OM MI MC n n n n − + = (9 15) Here, OM, MI and MC represent magnitudes of distances Applying the Cartesian sign convention, OM = –u, MI = +v, MC = +R Substituting these in Eq (9
9
382-385
15) Here, OM, MI and MC represent magnitudes of distances Applying the Cartesian sign convention, OM = –u, MI = +v, MC = +R Substituting these in Eq (9 15), we get 2 1 2 1 n n n n v u −R − = (9
9
383-386
Applying the Cartesian sign convention, OM = –u, MI = +v, MC = +R Substituting these in Eq (9 15), we get 2 1 2 1 n n n n v u −R − = (9 16) Equation (9
9
384-387
(9 15), we get 2 1 2 1 n n n n v u −R − = (9 16) Equation (9 16) gives us a relation between object and image distance in terms of refractive index of the medium and the radius of curvature of the curved spherical surface
9
385-388
15), we get 2 1 2 1 n n n n v u −R − = (9 16) Equation (9 16) gives us a relation between object and image distance in terms of refractive index of the medium and the radius of curvature of the curved spherical surface It holds for any curved spherical surface
9
386-389
16) Equation (9 16) gives us a relation between object and image distance in terms of refractive index of the medium and the radius of curvature of the curved spherical surface It holds for any curved spherical surface Example 9
9
387-390
16) gives us a relation between object and image distance in terms of refractive index of the medium and the radius of curvature of the curved spherical surface It holds for any curved spherical surface Example 9 5 Light from a point source in air falls on a spherical glass surface (n = 1
9
388-391
It holds for any curved spherical surface Example 9 5 Light from a point source in air falls on a spherical glass surface (n = 1 5 and radius of curvature = 20 cm)
9
389-392
Example 9 5 Light from a point source in air falls on a spherical glass surface (n = 1 5 and radius of curvature = 20 cm) The distance of the light source from the glass surface is 100 cm
9
390-393
5 Light from a point source in air falls on a spherical glass surface (n = 1 5 and radius of curvature = 20 cm) The distance of the light source from the glass surface is 100 cm At what position the image is formed
9
391-394
5 and radius of curvature = 20 cm) The distance of the light source from the glass surface is 100 cm At what position the image is formed Solution We use the relation given by Eq
9
392-395
The distance of the light source from the glass surface is 100 cm At what position the image is formed Solution We use the relation given by Eq (9
9
393-396
At what position the image is formed Solution We use the relation given by Eq (9 16)
9
394-397
Solution We use the relation given by Eq (9 16) Here u = – 100 cm, v =
9
395-398
(9 16) Here u = – 100 cm, v = , R = + 20 cm, n1 = 1, and n2 = 1
9
396-399
16) Here u = – 100 cm, v = , R = + 20 cm, n1 = 1, and n2 = 1 5
9
397-400
Here u = – 100 cm, v = , R = + 20 cm, n1 = 1, and n2 = 1 5 We then have 1
9
398-401
, R = + 20 cm, n1 = 1, and n2 = 1 5 We then have 1 5 1 0
9
399-402
5 We then have 1 5 1 0 5 100 20 v + = or v = +100 cm The image is formed at a distance of 100 cm from the glass surface, in the direction of incident light
9
400-403
We then have 1 5 1 0 5 100 20 v + = or v = +100 cm The image is formed at a distance of 100 cm from the glass surface, in the direction of incident light FIGURE 9
9
401-404
5 1 0 5 100 20 v + = or v = +100 cm The image is formed at a distance of 100 cm from the glass surface, in the direction of incident light FIGURE 9 15 Refraction at a spherical surface separating two media
9
402-405
5 100 20 v + = or v = +100 cm The image is formed at a distance of 100 cm from the glass surface, in the direction of incident light FIGURE 9 15 Refraction at a spherical surface separating two media Rationalised 2023-24 Physics 234 9
9
403-406
FIGURE 9 15 Refraction at a spherical surface separating two media Rationalised 2023-24 Physics 234 9 5
9
404-407
15 Refraction at a spherical surface separating two media Rationalised 2023-24 Physics 234 9 5 2 Refraction by a lens Figure 9
9
405-408
Rationalised 2023-24 Physics 234 9 5 2 Refraction by a lens Figure 9 16(a) shows the geometry of image formation by a double convex lens
9
406-409
5 2 Refraction by a lens Figure 9 16(a) shows the geometry of image formation by a double convex lens The image formation can be seen in terms of two steps: (i) The first refracting surface forms the image I1 of the object O [Fig
9
407-410
2 Refraction by a lens Figure 9 16(a) shows the geometry of image formation by a double convex lens The image formation can be seen in terms of two steps: (i) The first refracting surface forms the image I1 of the object O [Fig 9
9
408-411
16(a) shows the geometry of image formation by a double convex lens The image formation can be seen in terms of two steps: (i) The first refracting surface forms the image I1 of the object O [Fig 9 16(b)]
9
409-412
The image formation can be seen in terms of two steps: (i) The first refracting surface forms the image I1 of the object O [Fig 9 16(b)] The image I1 acts as a virtual object for the second surface that forms the image at I [Fig
9
410-413
9 16(b)] The image I1 acts as a virtual object for the second surface that forms the image at I [Fig 9
9
411-414
16(b)] The image I1 acts as a virtual object for the second surface that forms the image at I [Fig 9 16(c)]
9
412-415
The image I1 acts as a virtual object for the second surface that forms the image at I [Fig 9 16(c)] Applying Eq
9
413-416
9 16(c)] Applying Eq (9
9
414-417
16(c)] Applying Eq (9 15) to the first interface ABC, we get 1 2 2 1 1 1 OB BI BC n n n −n + = (9
9
415-418
Applying Eq (9 15) to the first interface ABC, we get 1 2 2 1 1 1 OB BI BC n n n −n + = (9 17) A similar procedure applied to the second interface* ADC gives, 2 1 2 1 1 2 DI DI DC n n n −n − + = (9
9
416-419
(9 15) to the first interface ABC, we get 1 2 2 1 1 1 OB BI BC n n n −n + = (9 17) A similar procedure applied to the second interface* ADC gives, 2 1 2 1 1 2 DI DI DC n n n −n − + = (9 18) For a thin lens, BI1 = DI1
9
417-420
15) to the first interface ABC, we get 1 2 2 1 1 1 OB BI BC n n n −n + = (9 17) A similar procedure applied to the second interface* ADC gives, 2 1 2 1 1 2 DI DI DC n n n −n − + = (9 18) For a thin lens, BI1 = DI1 Adding Eqs
9
418-421
17) A similar procedure applied to the second interface* ADC gives, 2 1 2 1 1 2 DI DI DC n n n −n − + = (9 18) For a thin lens, BI1 = DI1 Adding Eqs (9
9
419-422
18) For a thin lens, BI1 = DI1 Adding Eqs (9 17) and (9
9
420-423
Adding Eqs (9 17) and (9 18), we get n n n n 1 1 2 1 1 1 OB DI BC DC 1 2 + = − +     ( ) (9
9
421-424
(9 17) and (9 18), we get n n n n 1 1 2 1 1 1 OB DI BC DC 1 2 + = − +     ( ) (9 19) Suppose the object is at infinity, i
9
422-425
17) and (9 18), we get n n n n 1 1 2 1 1 1 OB DI BC DC 1 2 + = − +     ( ) (9 19) Suppose the object is at infinity, i e
9
423-426
18), we get n n n n 1 1 2 1 1 1 OB DI BC DC 1 2 + = − +     ( ) (9 19) Suppose the object is at infinity, i e , OB ® ¥ and DI = f, Eq
9
424-427
19) Suppose the object is at infinity, i e , OB ® ¥ and DI = f, Eq (9
9
425-428
e , OB ® ¥ and DI = f, Eq (9 19) gives fn n n 1 2 1 1 1 = − +     ( ) BC DC 1 2 (9
9
426-429
, OB ® ¥ and DI = f, Eq (9 19) gives fn n n 1 2 1 1 1 = − +     ( ) BC DC 1 2 (9 20) The point where image of an object placed at infinity is formed is called the focus F, of the lens and the distance f gives its focal length
9
427-430
(9 19) gives fn n n 1 2 1 1 1 = − +     ( ) BC DC 1 2 (9 20) The point where image of an object placed at infinity is formed is called the focus F, of the lens and the distance f gives its focal length A lens has two foci, F and F¢, on either side of it (Fig
9
428-431
19) gives fn n n 1 2 1 1 1 = − +     ( ) BC DC 1 2 (9 20) The point where image of an object placed at infinity is formed is called the focus F, of the lens and the distance f gives its focal length A lens has two foci, F and F¢, on either side of it (Fig 9
9
429-432
20) The point where image of an object placed at infinity is formed is called the focus F, of the lens and the distance f gives its focal length A lens has two foci, F and F¢, on either side of it (Fig 9 16)
9
430-433
A lens has two foci, F and F¢, on either side of it (Fig 9 16) By the sign convention, BC1 = + R1, DC2 = –R2 So Eq
9
431-434
9 16) By the sign convention, BC1 = + R1, DC2 = –R2 So Eq (9
9
432-435
16) By the sign convention, BC1 = + R1, DC2 = –R2 So Eq (9 20) can be written as (9
9
433-436
By the sign convention, BC1 = + R1, DC2 = –R2 So Eq (9 20) can be written as (9 21) Equation (9
9
434-437
(9 20) can be written as (9 21) Equation (9 21) is known as the lens maker’s formula
9
435-438
20) can be written as (9 21) Equation (9 21) is known as the lens maker’s formula It is useful to design lenses of desired focal length using surfaces of suitable radii of curvature
9
436-439
21) Equation (9 21) is known as the lens maker’s formula It is useful to design lenses of desired focal length using surfaces of suitable radii of curvature Note that the formula is true for a concave lens also
9
437-440
21) is known as the lens maker’s formula It is useful to design lenses of desired focal length using surfaces of suitable radii of curvature Note that the formula is true for a concave lens also In that case R1is negative, R 2 positive and therefore, f is negative
9
438-441
It is useful to design lenses of desired focal length using surfaces of suitable radii of curvature Note that the formula is true for a concave lens also In that case R1is negative, R 2 positive and therefore, f is negative FIGURE 9