## natasha.aries one year ago ***PLEASE HELP! TEST TOMORROW!*** An object is placed 10.0 cm in front of a mirror. what type must the mirror be to form an image of the object that is 2.00 m away from the mirror? what is the magnification of the image?

1. natasha.aries

I got -5 as the magnification, and it also asked whether it was virtual or real, and upright or inverted. I said it virtual and upright.. Can anyone tell me if I am right?

2. LastDayWork

What do you understand by "..away from the mirror.." ??

3. dumbcow

sorry i am not familiar with these type of problems

4. natasha.aries

Its okay @dumbcow

5. natasha.aries

and what do you mean @LastDayWork

6. dumbcow

i did find this, it may help http://en.wikipedia.org/wiki/Magnification#Calculating_the_magnification_of_optical_systems

7. LastDayWork

Away from the mirror can imply either side..real and virtual..

8. LastDayWork

@Mashy Can you help here ??

9. Mashy

Ok.. first u need to decide if its Convex mirror or Concave mirror.. (its not plain, cause in plain object distance = image distance) now can u first tell me is it convex or concave? (think properly.. u ll get it.. @LastDayWork.. i hope u know which one it is :P)

10. LastDayWork

XD

11. natasha.aries

its convex right?

12. Mashy

why do u think its convex?

13. Mashy

draw a general ray diagram for convex.. showing objects and images.. then u ll be able to uderstand..

14. natasha.aries

but it doesnt give you enough information to decide which one it is?

15. Mashy

the info is not needed.. only one of them is possible.. just draw a ray diagram.. i am telling.. that ll make u understand!

16. natasha.aries

i drew it and still dont see how it isnt convex

17. natasha.aries

oh wait! is it concave outside?

18. Mashy

if u drew it properly.. which distance u see bigger? object distance or image distance ?

19. Mashy

|dw:1392185681486:dw| this is kinda what the ray diagram is... see where the image is formed..

20. natasha.aries

yeah...

21. Mashy

so which distance is bigger in case of convex? object or image?

22. natasha.aries

object

23. Mashy

good.. so the image is ALWAYS.. ALWAYSSSS.. magnified or diminshed ?

24. natasha.aries

diminished

25. Mashy

so.. now u understand.. why in the rear view mirrors.. they say 'objects are closer than they appear" cause the images are always diminshed.. and we will THINK.. that they are far away.. cause our stupid brains say "hey that car looks small.. so it must be far" ok.. now.. we nailed it down.. that its concave.. right?.. but we are not done yet.. there are stil two possibilities! In concave..

26. natasha.aries

yeah! would it be concave outside?

27. Mashy

what u mean concave outside? o.O

28. Mashy

there is only one type of concave :P

29. natasha.aries

you said there are two possibilities

30. Mashy

i meant.. in concave mirror itself.. there are two places u can keep the object.. such that u get image 2m away. can you think which are the two cases ?

31. natasha.aries

in front of and behind

32. Mashy

u can't be something BEHIND the mirror.. if u go BEHIND the mirror.. there is NO reflection darling!

33. natasha.aries

like inside the focal point and behind the focal point

34. Mashy

Ahaa.. yea.. thats the one so if the object is kept Between the mirror (pole) and the focal point.. will u get real or virtual image?

35. natasha.aries

virtual

36. Mashy

perfect.. will this be magnified or diminished ?

37. natasha.aries

magnified

38. Mashy

yuppeerrss so.. it could be this case.. so the image could be virtual.. and magnified.. so in this case the magnification is positive hence in this case... magnification = + 200/10 = 20 ( i wonder how u got 5 as the answer o.O) now is it possible to keep the object in such a way, that u get a real enlarged image?

39. natasha.aries

so would it be the concave that is in front of the focal point just because we have to get a real image and not a virtual one?

40. natasha.aries

and where did you get 200 from?

41. Mashy

you mean "outside its focal point?" YES so in this case ALSO the given condition is satisfied hence.. in this case, the magification is negative magnification = image distance/ object distance ( i am not considering signs .. cause i dunno what sign convention u use.. don't wanna confuse u.. ) image distance = 2m = 200cm object distance = 10cm

42. Mashy

so in the real case u would end up with Real image, and -20 as the magnification!

43. natasha.aries

ohh! okay! thank you sooo muchh

44. Mashy

no problem! :) :)!

45. natasha.aries

:)