Sign Conventions For Lenses
Sign Conventions For Lenses
With thin lenses, we generally come across three distances parallel to and two distances perpendicular to the principal axis. Each of these distances we define a particular quantity and a symbol is assigned to it. These quantities are given in table.
| Distance | Quantity | Symbol |
| From the optical centre to the object | object-distance | |
| From the optical centre to the image | image-distance | |
| From the optical centre to second principal focus | focal length | |
| Height of the object | object-height | |
| Height of the image | image-height |
The above definitions of u and v are for a point object placed on the principal axis. If an object is placed away from the principal axis, u corresponds to the distance from the optical centre to the foot of the perpendicular drawn from the object to the principal axis. Similarly, v corresponds to the distance from the optical centre to the foot of the perpendicular drawn from the image to the principal axis. The quantities and
are defined for a linear, extended object placed perpendicular to the principal axis.
For finding a particular distance when some other are given, we need to assign these quantities positive or negative signs according to a fixed set of rules, or a convention. Several conventions for the signs of these quantities are in use. We shall follow the Cartesian coordinates convention.
1 Transverse distances are measured from the optical centre.If the object or image is present above the principal axis than it is taken as positive that is positive y axis while those are below taken as negative that is negative y axis.
2 Longitudinal distances are also measured from the optical centre and taken as positive if they are in the direction of propagation of incident light that is positive x axis and taken as negative if they are in opposite direction that is negative x-axis..
|
Coordinate convention For u, v, f |
|
|
Coordinate Convention for |
|
Note that in this convention, f is negative for a concave lens and positive for a convex lens. Also, heights above the principal axis are positive and those below it are negative.
Students / Parents Reviews [10]
It was good as the experience because as we had come here we had been improved in a such envirnment created here.Extra is taught which is beneficial for future.
Eshan Arora
8thIt has a great methodology. Students here can get analysis to their test quickly.We can learn easily through PPTs and the testing methods are good. We know that where we have to practice
Barkha Arora
10thA marvelous experience with Abhyas. I am glad to share that my ward has achieved more than enough at the Ambala ABHYAS centre. Years have passed on and more and more he has gained. May the centre flourish and develop day by day by the grace of God.
Archit Segal
7thMy experience with Abhyas is very good. I have learnt many things here like vedic maths and reasoning also. Teachers here first take our doubts and then there are assignments to verify our weak points.
Shivam Rana
7thAbhyas is a complete education Institute. Here extreme care is taken by teacher with the help of regular exam. Extra classes also conducted by the institute, if the student is weak.
Om Umang
10thAbhyas Methodology is very good. It is based on according to student and each child manages accordingly to its properly. Methodology has improved the abilities of students to shine them in future.
Manish Kumar
10thOne of the best institutes to develope a child interest in studies.Provides SST and English knowledge also unlike other institutes. Teachers are co operative and friendly online tests andPPT develope practical knowledge also.
Aman Kumar Shrivastava
10thBeing a parent, I saw my daughter improvement in her studies by seeing a good result in all day to day compititive exam TMO, NSO, IEO etc and as well as studies. I have got a fruitful result from my daughter.
Prisha Gupta
8thIt was a good experience with Abhyas Academy. I even faced problems in starting but slowly and steadily overcomed. Especially reasoning classes helped me a lot.
Cheshta
10thAbout Abhyas metholodology the teachers are very nice and hardworking toward students.The Centre Head Mrs Anu Sethi is also a brilliant teacher.Abhyas has taught me how to overcome problems and has always taken my doubts and suppoeted me.
