Thursday, July 7, 2011

To determine the focal length of a concave mirror by far away image.

2. To determine the focal length of a concave mirror by obtaining an image of a far distance object

AIM :- To determine the focal length of a concave mirror by obtaining an image of a far distance object.
APPARATUS  :- A concave  mirror of diameter approximately 10 cm., stand, screen, foot-rule, etc.
PRINCIPLE   :- Rays coming from a far distance object are almost parallel. Such rays, parallel to the principal axis, after being reflected by a concave mirror, are focused at the principal focus of the mirror. Distance between the principal focus and the pole of the mirror is known as the focal length.
NOTE  :  Here screen should be taken small, so that rays coming from the object are    not blocked by the screen itself. Diameter of the screen here can be   approximately 3 – 4 cm.
Focal Length of Concave mirror
Parallal rays of a Image 
Focal length of image on concave mirror
OBSERVATION
Distance between the pole of the mirror and the image on the screen = focal-length =                            CM.
CONCLUSION
PRACTICAL USES
Concave mirrors are used in head lights of vehicles, solar furnace, solar cooker, shaving mrror, etc. For all such applcatons it is necessary to know the focal length of the mirror to used. It can be estimated using the given method.


Video
To determine the focal length of a concave mirror by obtaining an image of a far distance object.
Focal length of concave mirror of a far away image.wmv

Monday, July 4, 2011

Angle of Incidence, Angle of image through Glass Slab experiments for std 8 to 12


To draw the path of a ray passing through a glass slab and, hence, to measure the angle of incidence and the angle of image.
AIM : To draw the path of a ray passing through a glass slab and, hence, to measure the angle of incidence and the angle of image.
PRINCIPLE :     When an oblique ray of light enters from one      transparent medium to another transparent medium,  at the surface separating these two media, the light  ray changes its path. This phenomenon is called  refraction of light. When a ray of light passes through  a glass-slab, it is refracted twice, as a result of which, the emergent ray becomes parallel to the incident ray.
APPARATUS :   Glass –slab, Drawing-board, Drawing paper (White),  Foot-rule, Pencil, Pins, Push pins and Protractor.
Paper fit with pins and set Glass Slab


Ø  Fix a white drawing-paper on the drawing board using push pins.  Now place the glass-slab on it and mark its position PQRS by drawing its out-line using a pencil.
Draw Ray AB not perpendicular to PQ

Ø  Now draw a ray AB such that it is not perpendicular to PQ. Fix two pins upright with separation of 2-3 cm on this ray.
See Image from another side and set P3 P4
Ø    Now try to see the images of P1 and P2 from side RS and fix pins P3  and P4 upright so that images of P1 and P2 and pins P3 and P4 become collinear at their lower ends.
Remove pins and Glass slab
Ø  Now remove the slab and the pins obtain emergent ray CD by drawing a line passing through marks of P3 and P4, which intersects RS at C.
Ø  Join  B and C to complete the path of the ray. Now draw a normal MN to the surface PQ in such a way that it passes through B. Also       draw M’N’, through C to the surface RS.
Measure Angle of Incidence and Angle of Emergence.
Ø  Measure ÐAMB (Angle of Incidence) and ÐOCN’ (Angle of Emergence).
By changing Angle of Incidence repeat the experiment
Ø  Repeat the experiment for various values of angle of incidence AMB and note your observations in the table.