Ray Optics & Optical Instruments Flashcards by Hector .

Reflection of light

Ray comes back after striking a surface

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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

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Pole

Geometric center of mirror

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Centre of curvature

Center of sphere of which mirror is a part

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Principle axis

Line joining CoC & pole

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Radius of curvature

Dist btn CoC & pole

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Principal focus

Beam || to principal axis from a point f on the axis after reflection converges or diverges

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Focal length

Dist btn pole & focus of mirror

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Ray via P.F for concave mirror will be

|| to P.A

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Ray via CoC for concave mirror will be

Reflected back

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Ray directed to P.F for convex mirror will be

|| to P.A

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Ray directed to CoC for convex mirror will be

Reflected back

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Image btn C & F

Object beyond C
R.I, diminished

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Image at C

Obj at C
R.I, same size

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Image beyond C

Obj btn C & F
R.I, enlarged

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Image behind mirror

Obj btn F & P
Virtual erect, enlarged

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Relation btn F & R(deri)

R = 2f

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Mirror formula deri

1/f = 1/v + 1/u

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Linear magnification

Ratio of height of image to object
m = h’/H = -v/u

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Refraction

Change in path of light as it passes obliquely from 1 transparent medium to other

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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

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Refractive index

Ratio of speed of light from 1 medium to other
Sin i/sin r = n²¹

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Limitation of snell’s law

Not valid for normal coincidence
sin i/sin r = 0/0

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n²¹ =

n2/n1 = v1/v2 = lambda1/lambda 2

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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:

1. To deviate ray via 90 2. To invert image with deviation via 180 3. 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

1. Due to large aperture, they have high resolving power 2. It is free from chromatic aberrations 3. Reduces spherical aberrations 4. 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