Similarities of astronomical telescope and a compound microscope

• consists of two convex lenses.
• The first image is real,inverted and acts as the object for the eyepiece.
• The eyepiece acts as a magnifying lens.(For an astronomical telescope in normal adjustment,the first image is at the common focal plane of the objective lens and the eyepiece.)
• The final image is virtual,invert and magnified.

 

Differences
Type of lens  

• Compound microscope:two high powered convex lenses
• Astronomical telescope:a low powered convex lens and a high powerted convex lens

First image

• Compound microscope:first image is magnified
• Astronomical telescope:first image is dimnished

Condition of the eye when using the instrument

• Compound microscope:ciliary muscles are at ease and the eye is relaxed
• Astronomical telescope:ciliary muscles are contracted.Eye is strained.   

  Ray Diagram

1. We can use ray diagram to determine the position and characteristic of images formed by lenses for any position of the object.
2. Ray diagram can be complete using any two out of the three rays of light.

  Rules for ray diagram:

convex lens

•  a ray of light which passes through the optical centre,O of the lens is undeviated.
• a ray  of light parallel to the principal axis is refracted and passes through the principal focus,F.
• a ray of light which passes through the principal focus,F is refracted parallel to principal axis.

concave lens

• a ray of light which passes through the optical centre,O is undeviated.
• a ray of light parallel to the principal axis is refracted and appears to come from the principal focus,F on same side of lens.
• a ray of light which travel towards the principal focus,F on the other of the lens is refracted parallel to the principal axis.

          *any two of the three rays point 1,2 and 3 are sufficient      to determine the position and characteristics of the image*

  Differences between convex and concave lenses

Convex lenses                                        

• Convex lenses are also known as converging lenses or positive lenses.    

• Convex lenses are thicker in the centre than at the adge.  

• Convex lenses refract incident rays of light,which are parallel to the principal   axis. This point is called the real principal focus.

Concave lenses

• Concave lenses are also known as diverging lenses or negative lenses.
• Concave lenses are thinner in the centre than at edge.
• Concave lenses refract incident rays of light,which are parallel to the principal axis,so that they appear to diverge from a point located on the incident side of the principal axis.This point is called the virtual principal focus.  
  

                                   

Total Internal Reflection

• total internal reflection is the total reflection of a beam of light at the   boundary of two mediums,when the angle of incidence in the optically denser medium exceeds a specific critical angle.
• the boundary between the two mediums acts like a perfect plane mirror where total internal reflection occurs.
• the critical angle is the angle of incidence in the optically denser medium for which the angle of reflection in the less dense medium is 90'.
• the conditions required for the occurence of total internal reflection are:

1. the light ray must travel from an optically denser medium to a less dense medium.
2. the angle of incidence must be greater than the critical angle,that is i>c

• example:it will occur when passing from glass to air.

Application-application of total Internal Reflection 

• optical fibres -> used in endoscopes and telecommunications.
• rain sensors -> to control automatic windscreen.
• prismatic binoculars -> to get a very clear image.
• gonioscopy -> to view the anatomical angle formed between the eye's cornea   and iris.
• fingerprinting devices -> to record an image of a person's fingerprint without the use of ink.

Causes of Reflection

• When a ray of light is reflected from a smooth surface, the angle of incidence is equal to the angle of reflection (i = r).

• The incident ray, the reflected ray and the normal all lie in the same plane.

Phenomenon of refraction

Diagram of refraction

Meaning of refraction

•   refraction of light is the change in direction or bending of the light as it enters from one medium to another.
•  It is caused by the change in the velocity in which the velocity of light is lower is an optically denser medium.
• Refraction is  described by snell’s law ,which states that when a ray of light travels from vacuum (or air) at an angle of incidence ,I and refracted into a medium at an angle of refraction ,r.
•  n= sin i / sin r

Application of convex mirror

qRear-view Mirror

•Convex mirror are used as rear-view mirror in motor vehicles to give drivers a wide-angle view of the vehicles behind them.

qWide-angle view Mirror

•  Concave mirror are hung from the corners of supermarket ceilings to provide a wider field of vision of the activities taking place in the shopping areas.

qSafety mirrors

•Convex mirrors are also mounted at sharp corners of roads so that drivers are able to see oncoming cars on their blind slide.

Applications of concave mirror

     Reflector

Concave parabolic mirror are used as reflectors in torch light and car headlight. 
Magnifying Mirror

Concave mirror in dentist’s mirror magnifies the image so that the dentist can get a closer look at the teeth.

Make-up Mirror 
For this purpose ,a wide-aperture concave mirror with a large radius of curvature is used.

Application1-reflection

One application is in the construction of telescopes, microscopes, CD-ROM drives, and other devices that use optical devices. The reflection of light, through lenses or against mirrors, is highly important. Symmetry is also used in graphic design, engineering, and architecture, to create stable and/or visibly pleasing buildings, signs, graphics, logos, etc.

Convex mirror

Differences between concave mirror and convex mirror

•Rays parallel to the principal axis converge to a point, called the real focal point, on the principal axis.

•PF = Focal length ,f

           = Distance between the real    focal point and the pole of  the mirror

        Example :f=+20cm

Concave mirror

 

Specular reflection

Diagram of reflection

Laws of reflection

• When a ray of light is reflected from a smooth surface, the angle of incidence is equal to the angle of reflection.

• The incident ray, the reflected ray, and the normal all lie in the same plane.

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