Suppose a convex mirror has a focal length of 120 cm. A candle sits directly in front of the mirror. If the image of that candle appears to be 24 cm behind the mirror, how far is the candle from the surface of the mirror?
A. 30 cm
B. 36 cm
C. 150 cm
D. 600 cm
Does any one know the answer?

Question

Suppose a convex mirror has a focal length of 120 cm. A candle sits directly in front of the mirror. If the image of that candle appears to be 24 cm behind the mirror, how far is the candle from the surface of the mirror?
  A. 30 cm
  B. 36 cm
  C. 150 cm
  D. 600 cm
Does any one know the answer?

TrinL3 · Answer

I was trying to figure it out, but I wasn't sure how to calculate it on the online diagram because of the 120cm focal length.

IhelpUuHELPme · Answer

o-o

So the mirror equation is:

|dw:1634165798357:dw|

f is the focal length

$$d _{o}$$ :
-the distance of the object from the mirror

$$d _{i}$$ :
-the distance of the image from the mirror

Going off of the formula, the focal length would be taken as a negative for a convex mirror, which this is so:

$$f = -120cm$$

It says in the problem that the image is *behind* the mirror meaning the sign of it is negative as well

$$d _{i} = -24cm$$

Now lets insert these numbers into the mirror equation(you can find the distance of the object FROM the mirror surface)

So this means that the distance of the object FROM the mirror is:

$$1 \over d _{o}$$   
equals

30cm

IhelpUuHELPme · Answer

hope that helped- rip- took me awhile smh

IhelpUuHELPme · Answer

Correct me if I'm wrong<3 (:

TrinL3 · Answer

@ihelpuuhelpme wrote:

hope that helped- rip- took me awhile smh

thanks so much that really helped!

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