## AaronAndyson one year ago An object is 25 cm away from a convex len.The height of the image is twice the height of the object.Find it's focal length.

1. AaronAndyson

@Abhisar

2. Abhisar

Ok, I am gonna tell you a Super Formula for lens $$\sf \boxed{M=\frac{V}{U}=\frac{f}{f+u}=\frac{f-v}{f}=\frac{h_i}{h_o}}$$

3. Abhisar

M= magnification, V=image distance u=object distance f=focal length $$\sf h_i~and~h_o$$ are image and object height respectively.

4. Abhisar

Note: You need to follow the cartasian coordinate.

5. AaronAndyson

Never heard of that :/

6. Abhisar

Heard of what? Cartasian cordinate

7. AaronAndyson

Never heard of this Cartasian cordinate

8. Abhisar

Do you know about the sign convension?

9. AaronAndyson

To be honest,I don't know a thing about Optics...

10. Abhisar

Ok, why don't you read this http://www.st-andrews.ac.uk/~bds2/optics/cartesian.html

11. AaronAndyson

Done.

12. AaronAndyson

How do I solve this problem?

13. Abhisar

Use the formula m = f/f+u

14. Abhisar

M is magnification. Because the height of the image is twice that of object so the magnification will be 2

15. Abhisar

You need to plug in the values with appropriate sign. that's it 2=f/f+ (-25)

16. AaronAndyson

-50 cm?

17. Abhisar

Re-check it should be in positive value

18. AaronAndyson

50 cm?

19. Abhisar

Yes.

20. AaronAndyson

Thanks

21. Abhisar

Welcome c: