## Aadarsh 3 years ago The magnification of a magnifying lens of focal length 5 cm is :(final image is at infinity) a) 1 b) 2 c) 3 d) 5

1. salini

wat si the type of lens that magnifies ur imge and also produces a virtual image? answer this question then wat is the ray diagram for getting image at infinity with that type of lens? wat is lens formula relating f,u,v i can get my v from that? wat is magnification? in terms of u and v u are near the answer once u have ansered all these questions

The lens must be a convex lens. The object is at focus.

\[1/v - 1/u = 1/f\]

Here, v = 0

Also, m = v/u

But, I am not getting the answer.

7. salini

put down the ray diagram for me when image is at infinity for convex lens

Just one minute. Here is the diagram.

|dw:1333555806014:dw|

@salini didi, Now say what to do.

11. salini

yeah so? u=?

12. salini

object disatnce=?

u = 5

14. salini

then? tell me how do i proceed?

m = f/(f+u) = 5/(5+5) = 0.5?????

16. salini

m=v/u u never used taht?

But how to do? Please say in detail the complete steps.

18. salini

u know that formula?

20. salini

i forgot for lenses tahts y ia m asking u

Ohhhhhhh!!! Can u please post the details tomorrow? I have to go now. Bye.

22. salini

ok bye! see pg.182 of 10th ncert text book

Okay, will look and say tomorrow.

Its given that, m = v/u = h1 / h2

25. salini

yeah so u know u, find V using lens formula then apply u/v to find magnification(the extent to which the image is magnified w.e.to object) the key here is taht u=focal length that u will come to know ONLY WHEN U DRAW THE RAY DIAGRAM!

But, v = 0 na?

27. salini

1/f=1v-1/u 1/v=1/f+1/u by sign convention f=-5 u=-5

@salini didi, then, m = f/(f+u) = 5[5 + (-5)] = 5/0?????

29. salini

v=?

v = 0, rite?

31. salini

U learnt ssign convention?>

yeah. U try and see. This problem uses some different formula. Then only we can get it.

33. salini

i will get back to you later after searching abt this problem

OK.

35. salini
36. salini

U r correct didi!!!!!! Cheers!!!!!!! thanks for the solution.

38. salini

:) we learn nothing...........there is so much to learn further

Oooooooooo. But, it is a continous process. Being happy is also a continuous process. So, be happy!!!!!!:P

40. salini

!!!!!!!!!!!!!!!!!! i dont know wat to type :)

Hehehehheheheheh!!!!!!!!!! Crazy Sister!!!!!!!!!!!!!