Ray Optics & Optical Instruments Flashcards
Reflection of light
Ray comes back after striking a surface
Laws of reflection
1st: angle of incidence is = angle of reflection
2nd: incident ray, reflected ray & normal at point of incidence all lie at the same plane
Pole
Geometric center of mirror
Centre of curvature
Center of sphere of which mirror is a part
Principle axis
Line joining CoC & pole
Radius of curvature
Dist btn CoC & pole
Principal focus
Beam || to principal axis from a point f on the axis after reflection converges or diverges
Focal length
Dist btn pole & focus of mirror
Ray via P.F for concave mirror will be
|| to P.A
Ray via CoC for concave mirror will be
Reflected back
Ray directed to P.F for convex mirror will be
|| to P.A
Ray directed to CoC for convex mirror will be
Reflected back
Image btn C & F
Object beyond C
R.I, diminished
Image at C
Obj at C
R.I, same size
Image beyond C
Obj btn C & F
R.I, enlarged
Image behind mirror
Obj btn F & P
Virtual erect, enlarged
Relation btn F & R(deri)
R = 2f
Mirror formula deri
1/f = 1/v + 1/u
Linear magnification
Ratio of height of image to object
m = h’/H = -v/u
Refraction
Change in path of light as it passes obliquely from 1 transparent medium to other
Laws of refraction
1st: law of reflection
2nd: ratio of sine of angle of incidence to sine of angle of Refraction is const for a given media & given color
Refractive index
Ratio of speed of light from 1 medium to other
Sin i/sin r = n²¹
Limitation of snell’s law
Not valid for normal coincidence
sin i/sin r = 0/0
n²¹ =
n2/n1 = v1/v2 = lambda1/lambda 2
Unit for refractive index
None
Absolute refractive index
Ratio of speed of light in vacuum to speed of light in medium
Ray from rarer to denser bends
Towards normal
Ray going along normal passes
Undeflected
Refractive index depends on
Wavelength, temp, nature of medium, speed of light
Lateral shift
When a ray passes via || sided retracting medium, the perp dist btn the emergent ray & direction of incidence is lateral shift
Normal shift
Apparent shift in the position of an obj when kept in 1 medium viewed normally from other
n²¹ = h’/h =
Real depth/apparent depth
Normal shift =
n(1 - 1/n¹²)
Apparent shift in position of sun in sunrise & sunset
Due to atmospheric Refraction, sun is visible before actual sunrise & after actual sunset. The refractive index of air is approx 1 w.r.t vacuum. So shift is in the direction of sun is by ½ degree & time diff btn actual & apparent sunrise & sunset is about 2 mins
Total internal reflection
As angle of incidence increases, angle of Refraction also increases. At an angle of incidence i=i(c), the angle of Refractionis 90°. When angle of incidence is more than i(c), it reflects back into denser medium
Critical angle
Angle of incidence in denser medium for which angle of Refraction is 90°
Relation btn critical angle & refractive index
n = 1/sin i(c)
Applications of TIR
Mirage observed in deserts & on tar roads due to Refraction & TIR
Sparkling of diamond
Totally reflecting prisms
Optical fibres
Uses of optical fibre
Transmitting & receiving electrical signals as light
Medical & optical examination
Endoscopy
Decorative lamps
Optic centre
Centre of lens
Centre of curvature
Center of sphere of which lens is a part
Radius of curvature
Dist btn center & optic centre
Totally reflecting prisms:
- To deviate ray via 90
- To invert image with deviation via 180
- To invert image without deviation
optical fibre core is surrounded by glass or plastic jacket of lower RI called
cladding
Power of a lens
Tangent of angle by which lens converges or diverges a beam of light at unit distance from optic center
Linear magnification for simple microscope
m = 1 + D/f
Magnification for compound microscope
m(o) = L/f(o)
m(e) = 1 + D/f(e)
When object is at infinity, m(e) =
D/f(e)
total magnification by compound microscope m =
m = m(o)m(e)
= L/f(o)(1 + D/f[(e)]
= V(o)/U(o)[1 + D/f(e)]
when object is at infinity, total magnification of compound microscope?
m = L/f(o)[D/f(e)]
When image is at D, L =
V(o) + U(e)
When image is at infinity, L =
Vo + f(e)
Refracting telescopes are used for
Viewing distant objects
Astronomical telescopes are used for
Viewing celestial objects
Terrestrial telescopes are used for
distant objects on earth
Reflecting telescopes are used for
Distant objects
Reflecting telescopes examples
Newtonian, cassegrain
magnification for astronomical telescopes
m = fo/fe
At D, m = fo/fe[1 + D/fe]
Advantages of reflecting telescope over refracting
- Due to large aperture, they have high resolving power
- It is free from chromatic aberrations
- Reduces spherical aberrations
- Lightweight, so mounting will be easy
If image converge, obj is
real
If Object converge, image is
virtual
If lens is cut horizontal, focal length is
same
If lens is cut vertical, focal length is
doubled
Denser to rarer, Object size
increases
N2/N1 =
V1/V2
When i>r
V1>V2
If lower half of concave mirror is covered, what will be the image?
Image with less intensity will be shown but full image will be shown
If a lens disappears in a liquid, what is the R.I of the liquid?
Same as lens
