# Mirror Review...

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#### chandler742

##### Senior Member
7+ Year Member
15+ Year Member

If an object is placed on the focal point that is 10 cm from a converging mirror, where is the image?

A) less or equal to 10 cm "inside" the mirror(i.e. virtual image)
B) on the focal point
C) an infinite distance inside the mirror
D) an infinite distance away from the mirror

Case 2

What if the object is placed 3 cm from the mirror, and between the focal point and the mirror of a concave mirror?

#### rCubed

##### taiko master
10+ Year Member
15+ Year Member
what do u mean by inside the mirror and outside the mirror?

its either C or D

for case 2: a virtual mirror would be formed

by the way, i think its awesome of u to post up all these questions...thanks alot

#### I to A

##### Member
7+ Year Member
15+ Year Member
Question 1:

f=10, D-o, 10, D-i ?

D-o, object distance and D-i, image distance

1/10=1/10+1/D-i

Question 2:

1/10 = 1/3 + 1/Di

Multiply either side by 10

1 = 3.3 + 10/Di

1-3.3 = 10/Di

-2.3= 10/Di

D-i = - (10/2.3)

negative, so the image is virtual which means on the other side of the mirror.

#### limit

##### Molesting my inner-child
10+ Year Member
15+ Year Member
#1 - Using the thin lens equation, the distance of the imagine approachesd infinity when moved towards the focal point from outside the focal point, forcing me to believe that the imagine is infinitely far away from the mirror -- answer choice D.

#2 - A concave, aka converging, mirror will produce a virtual image (behind the mirror), with a distance away from it as that described by the above poster.

#### chandler742

##### Senior Member
7+ Year Member
15+ Year Member
2 for 2, good job limit. If you are taking the MCAT next week, I think you will smoke physics.

what i mean "inside" the mirror is that the image is actually virtual and seems like it is coming from inside the mirror.

Also, the reason I put the object on the focal point is that most students tend to just use 1/p + 1/q =1/F without thinking about what they are doing.

Notice, if you just plug and chug chances are you might wonder what happened? as 1/q = 0

i.e. 1/over infinity.

If interested aka. extra information

As for which side the image is coming from i.e from the mirror or away, if you draw a ray diagram you will notice that an object is on the side opposite of the mirror.

Convex mirrors are easier as they are always Virtual and Erect.

#### limit

##### Molesting my inner-child
10+ Year Member
15+ Year Member
Originally posted by chandler742
2 for 2, good job limit. If you are taking the MCAT next week, I think you will smoke physics.
I am, thanks for the encouragement.
what i mean "inside" the mirror is that the image is actually virtual and seems like it is coming from inside the mirror.
Gotcha, though I have personally never heard it stated that way.
Regardless, such should occur in a convex mirror(?)