.. 16 Define optical path ofa mcdi_um . .
· d s defined as the
8. What is P<?le? , is called Optical path of a me ium .1 . it
6.0PTICS - RA y OPTICS The geometrical center of the mirror distant d' light travels in vacuum m the same time
pole (P) of the mirror. travels a distance d in the medium.
2 MARK QUESTIONS
9. What is principal axis? f 17. State laws of refraction.
I. What is reflection? . The line joining the pole and the c~ntre o
The bouncing back of light in the same_ medium (a) The incident ray. refracted ray and normal to the
a reflecting surface is called curvature is called the principal axis of the nurror. reflecting surface all are coplanar.
when it encounters
I
reflection of light. (b) ~=~
sin r n1
10. What is focal point? h
Light rays travelling parallel and cl~se to_ t e
2. State laws of reflection. What is angle of deviation due to refraction of light?
(a) The incident ray, reflected ray and normal to the principal axis when incident on of spherical mirror 18.
converge at a point for concave mirror or appear to ·• The angle between the incident and deviated
reflecting surface all are coplanar.
(b) The angle of incidence; is equal to the angle of diverge from a point for convex mirror on the light is called angle of deviation.
reflection r. ( i = r) principal axis. This point is called the focus or focal When light travels from rarer to denser medium
point ( F) ~fthe mirror. it deviates towards normal. d = i - r
3. What is angle of deviation due to reflecHon? . When light travels from denser to rarer medium
The angle between the incident and deviated 11. What is focal length? it deviates away from normal, d = r - i
light ray is called angle of deviation of the light ray. :T he distance between the pole and the focus is
called the focal length (f) of the mirror. 19. State the principle of reversibility.
4. What is virtual image? The principle of reversibility state that light will
The image which cannot be formed on the screen 12. What is focal plane? follow exactly the same path if its direction oftra~el
but can only be seen with the eyes is called virtual l'fhe plane through the focus and perpendicular to
is reversed.
image . the principal axis is called the focal plane of the
mirror.'
s. What is real image? 20. What is ·relative refractive index?
The image which can be fom1ed on the screen 13 . . W!iat are paraxial rays? In the equation for Snell's law, the term~ is
and can also be seen with the eyes is called real The rays travelling very close to the principal called relative refractive index of the second
image. :axis and make small angles with it are called medium with respect to the first medium which is
1paraxial rays. denoted as n21
6. What is centre of curvature?
The centre of the sphere of which the mirror is a
14. What arc marginal rays? 21. What is critical angle?
part is called the centre of curvature ( C ) of the
mirror. The rays travelling far away from the principal The angle of incidence in the denser medium for
axis and fall on the mirror far away from the pole are which the refracted ray graces the boundary is called ,J
7. What is radius or curvature? called as marginal rays. critical angel i0
The radius of the sphere of which the spt,erical
mirror is a part is called the radius of curvawr, ( R) IS. Define refractive index. 22. What is total internal reflection?
of1he mirror. Refractive index of a transparent medium is
defined as the ratio of speed o flight in vacuum to
'
~
r
' '
••.
~<
, ............
If the angle of incidence in the denser medium
is increased beyond the critical angle. there is
, .2 4: ; -- •.
The entire light is reOected back into the denser 28. What is dispersion? 1 3 MARK QUESTI ONS :
medium itself. Dispersion is splitting of white light into its I. Give the characteristics of image formed by a plane
This phenomenon is called total internal constituent colours. This band of colours ·of light is mirror.
r -
,;-, reOc'ction. called its spectrum. *The image formed by a plane mirror is virtual,
erect, and laterally inverted . .
23 . What arc the conditions to take place total internal 29. Define dispersive power. *The size of the image is equal to the size of the
reflection? It is defined as the ratio of the angular dispersion Qbject.
*
Light must travel from denser to rarer me~ium for the extreme colours to the deviation for , any *The image distance far behind the mirror is
*
Angle of incidence in the denser medium' must mean colour. rqual to the object distance in front of it.
be greater than critical angle. ( i > c) 30. What is Rayleigh's scattering? *If an object is placed between two plane
If the scattering of light is by atoms and mirrors inclined at an angle 8, then the number
24. What is Snell's window? molecules which have size a very less than th~~ of of images n formed is as
* When light entering the water from outside is the wavelength l of light a « l, the scattering is * . 8360 .
1f 1s event hen, n = (3
8
6o )
.
.,-1 fior objects
,... seen from inside the water, the view is called Rayleigh's scattering. ' placed symmetrically or unsymmetrically,
restricted to a particular angle equal to the )
31. Why do stars twinkle? * If 8 360 .
1s od d t hen n = (360
- 1 fior obj.ects
critical angle I.. The stars actually do not twinkle. 8
* This restricted illuminated circular area is
They appear twinkling because of the
placed symmetrically.
called Snell's window.
movement of the atmospheric layers with * 1.f (360) . h
8 ,s odd t en, n = (360)
8 for objects
varying refractive indices which, is clearly ~ecn placed unsymmetrically.
2.5 . What are primary focus and secondary focus?
in the night sky.
Primary focus:
32. Why docs sky appear blue? 2. Derive the relation between / and R for a spherical
The primary focus FI is defined as a point where
According to Rayleigh's scattering law, violet mirror.
an object should be placed to give parallel emergent
rays to the principal axis. colour which has the shortest wavelength gets
Secondary focus: much scattered during day time.
The secondary focus F2 ls defined as a point • As our eyes arc more sensitive to blue colour
where all tho parallel ray ■ travellina close to the than violet colour the sky appears blue during
principal axis. day time.
33. Why do rain clouds appear dark?
26. What Is power of a lens? Give Its unit. The rain clouds appear dark because of the * Let C be the centre of curvature of the mirror.
* The power of a lens Is a measure of the degree condensation of water droplets on dust particles that * Consider a light ray parallel to the principal
of convergence or divergence of light falling on makes the cloud become opaque. axis is incident on the mirror at M and passes
it. through the principal focus F after reflection . '\
34. W:-.y docs sky appears dark for astronauts?
* P. lI • If earth has no atmosphere there would ' not * The line CM is the normal to the mirror at M.
* Its ur.it Is dioptre D have been any scattering and the sky would * Let i be the angle of incidence and the same
appear dark. will be the angle of reflection.
27. What Is angle of minimum deviation? • That is why sky appears dark for the astronauts * £MCP = i and £MFP = 2i
The minimum value of angle of deviation Is who could see the sky from above the * tan i = ~ and tan 2i = ~
~lied anale of minimum deviation D. atmosphere. * As the angles arc small tan i =- i
· d s defined as the
8. What is P<?le? , is called Optical path of a me ium .1 . it
6.0PTICS - RA y OPTICS The geometrical center of the mirror distant d' light travels in vacuum m the same time
pole (P) of the mirror. travels a distance d in the medium.
2 MARK QUESTIONS
9. What is principal axis? f 17. State laws of refraction.
I. What is reflection? . The line joining the pole and the c~ntre o
The bouncing back of light in the same_ medium (a) The incident ray. refracted ray and normal to the
a reflecting surface is called curvature is called the principal axis of the nurror. reflecting surface all are coplanar.
when it encounters
I
reflection of light. (b) ~=~
sin r n1
10. What is focal point? h
Light rays travelling parallel and cl~se to_ t e
2. State laws of reflection. What is angle of deviation due to refraction of light?
(a) The incident ray, reflected ray and normal to the principal axis when incident on of spherical mirror 18.
converge at a point for concave mirror or appear to ·• The angle between the incident and deviated
reflecting surface all are coplanar.
(b) The angle of incidence; is equal to the angle of diverge from a point for convex mirror on the light is called angle of deviation.
reflection r. ( i = r) principal axis. This point is called the focus or focal When light travels from rarer to denser medium
point ( F) ~fthe mirror. it deviates towards normal. d = i - r
3. What is angle of deviation due to reflecHon? . When light travels from denser to rarer medium
The angle between the incident and deviated 11. What is focal length? it deviates away from normal, d = r - i
light ray is called angle of deviation of the light ray. :T he distance between the pole and the focus is
called the focal length (f) of the mirror. 19. State the principle of reversibility.
4. What is virtual image? The principle of reversibility state that light will
The image which cannot be formed on the screen 12. What is focal plane? follow exactly the same path if its direction oftra~el
but can only be seen with the eyes is called virtual l'fhe plane through the focus and perpendicular to
is reversed.
image . the principal axis is called the focal plane of the
mirror.'
s. What is real image? 20. What is ·relative refractive index?
The image which can be fom1ed on the screen 13 . . W!iat are paraxial rays? In the equation for Snell's law, the term~ is
and can also be seen with the eyes is called real The rays travelling very close to the principal called relative refractive index of the second
image. :axis and make small angles with it are called medium with respect to the first medium which is
1paraxial rays. denoted as n21
6. What is centre of curvature?
The centre of the sphere of which the mirror is a
14. What arc marginal rays? 21. What is critical angle?
part is called the centre of curvature ( C ) of the
mirror. The rays travelling far away from the principal The angle of incidence in the denser medium for
axis and fall on the mirror far away from the pole are which the refracted ray graces the boundary is called ,J
7. What is radius or curvature? called as marginal rays. critical angel i0
The radius of the sphere of which the spt,erical
mirror is a part is called the radius of curvawr, ( R) IS. Define refractive index. 22. What is total internal reflection?
of1he mirror. Refractive index of a transparent medium is
defined as the ratio of speed o flight in vacuum to
'
~
r
' '
••.
~<
, ............
If the angle of incidence in the denser medium
is increased beyond the critical angle. there is
, .2 4: ; -- •.
The entire light is reOected back into the denser 28. What is dispersion? 1 3 MARK QUESTI ONS :
medium itself. Dispersion is splitting of white light into its I. Give the characteristics of image formed by a plane
This phenomenon is called total internal constituent colours. This band of colours ·of light is mirror.
r -
,;-, reOc'ction. called its spectrum. *The image formed by a plane mirror is virtual,
erect, and laterally inverted . .
23 . What arc the conditions to take place total internal 29. Define dispersive power. *The size of the image is equal to the size of the
reflection? It is defined as the ratio of the angular dispersion Qbject.
*
Light must travel from denser to rarer me~ium for the extreme colours to the deviation for , any *The image distance far behind the mirror is
*
Angle of incidence in the denser medium' must mean colour. rqual to the object distance in front of it.
be greater than critical angle. ( i > c) 30. What is Rayleigh's scattering? *If an object is placed between two plane
If the scattering of light is by atoms and mirrors inclined at an angle 8, then the number
24. What is Snell's window? molecules which have size a very less than th~~ of of images n formed is as
* When light entering the water from outside is the wavelength l of light a « l, the scattering is * . 8360 .
1f 1s event hen, n = (3
8
6o )
.
.,-1 fior objects
,... seen from inside the water, the view is called Rayleigh's scattering. ' placed symmetrically or unsymmetrically,
restricted to a particular angle equal to the )
31. Why do stars twinkle? * If 8 360 .
1s od d t hen n = (360
- 1 fior obj.ects
critical angle I.. The stars actually do not twinkle. 8
* This restricted illuminated circular area is
They appear twinkling because of the
placed symmetrically.
called Snell's window.
movement of the atmospheric layers with * 1.f (360) . h
8 ,s odd t en, n = (360)
8 for objects
varying refractive indices which, is clearly ~ecn placed unsymmetrically.
2.5 . What are primary focus and secondary focus?
in the night sky.
Primary focus:
32. Why docs sky appear blue? 2. Derive the relation between / and R for a spherical
The primary focus FI is defined as a point where
According to Rayleigh's scattering law, violet mirror.
an object should be placed to give parallel emergent
rays to the principal axis. colour which has the shortest wavelength gets
Secondary focus: much scattered during day time.
The secondary focus F2 ls defined as a point • As our eyes arc more sensitive to blue colour
where all tho parallel ray ■ travellina close to the than violet colour the sky appears blue during
principal axis. day time.
33. Why do rain clouds appear dark?
26. What Is power of a lens? Give Its unit. The rain clouds appear dark because of the * Let C be the centre of curvature of the mirror.
* The power of a lens Is a measure of the degree condensation of water droplets on dust particles that * Consider a light ray parallel to the principal
of convergence or divergence of light falling on makes the cloud become opaque. axis is incident on the mirror at M and passes
it. through the principal focus F after reflection . '\
34. W:-.y docs sky appears dark for astronauts?
* P. lI • If earth has no atmosphere there would ' not * The line CM is the normal to the mirror at M.
* Its ur.it Is dioptre D have been any scattering and the sky would * Let i be the angle of incidence and the same
appear dark. will be the angle of reflection.
27. What Is angle of minimum deviation? • That is why sky appears dark for the astronauts * £MCP = i and £MFP = 2i
The minimum value of angle of deviation Is who could see the sky from above the * tan i = ~ and tan 2i = ~
~lied anale of minimum deviation D. atmosphere. * As the angles arc small tan i =- i
