(easy) Finding variables with mirror equation

In summary, the student attempted to solve a homework problem, but was unsuccessful. They realized that they may have made a mistake in the second lens and asked their friends for help. Their friends told them that the most common number for Mtot is around 200.
  • #1
classi
3
0
This isn't exactly a homework problem, per se, but this was a district assessment I already took today. I was confident that I would get a good grade, but it turns out I got a measly 65%. I don't remember the exact wording, but I do remember the general idea of it.

Homework Statement


There are two lenses, both of which are 16cm apart. An object is 1.3cm away from the first lens.

First lens
f = 1.2cm
do = ?
di = ?
M = ?

Second lens
f = .42cm
do = ?
di = ?
M = ?

Total Magnification
Mtot = ?

Homework Equations


di = dof/do-f
M = di/do
Mtot = M1*M2

The Attempt at a Solution


First lens
f = 1.2cm
do = 1.3cm (given)
di = 15.6 cm
M = 12x

Second lens
f = .42
do = 16cm+1.3cm = 17.3cm
di = .43 cm
M = .025x

Total Magnification
Mtot = .3x
Looking back at it now, I think I messed up somewhere in the second lens.
I've asked friends what they got for Mtot, and the majority of them said a number around the 200s.

What am I doing wrong?
 
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  • #2
classi said:
This isn't exactly a homework problem, per se, but this was a district assessment I already took today. I was confident that I would get a good grade, but it turns out I got a measly 65%. I don't remember the exact wording, but I do remember the general idea of it.

Homework Statement


There are two lenses, both of which are 16cm apart. An object is 1.3cm away from the first lens.

First lens
f = 1.2cm

Second lens
f = .42cm

Total Magnification
Mtot = ?

Homework Equations


di = dof/do-f
M = di/do
Mtot = M1*M2

The Attempt at a Solution


First lens
f = 1.2cm
do = 1.3cm (given)
di = 15.6 cm
M = 12x

Second lens
f = .42
do = 16cm+1.3cm = 17.3cm
di = .43 cm
M = .025x

Total Magnification
Mtot = .3x

Looking back at it now, I think I messed up somewhere in the second lens.
I've asked friends what they got for Mtot, and the majority of them said a number around the 200s.

What am I doing wrong?
Hello classi. Welcome to PF !

The image formed by the first lens becomes the object for the second lens.
 
  • #3
Oh my gosh, thanks! :)
That makes perfect sense; I don't know why I didn't think of that before.
 

1. What is the mirror equation?

The mirror equation is a formula that relates the object distance, image distance, and focal length of a curved mirror. It is expressed as 1/o + 1/i = 1/f, where o is the object distance, i is the image distance, and f is the focal length.

2. How do I find the object distance?

The object distance is the distance between the object and the mirror. To find it, measure the distance from the object to the mirror in a straight line. This will be the value for o in the mirror equation.

3. How do I find the image distance?

The image distance is the distance between the image and the mirror. To find it, measure the distance from the mirror to the point where the image appears. This will be the value for i in the mirror equation.

4. What is the focal length and how do I find it?

The focal length is the distance between the center of the mirror and its focal point. To find it, measure the distance from the mirror to the point where the reflected rays converge. This will be the value for f in the mirror equation.

5. Are there any special cases for finding variables with the mirror equation?

Yes, there are two special cases. The first is when the object is located at infinity, in which case the object distance (o) is equal to 0 and the mirror equation becomes 1/i = 1/f. The second is when the object is placed at the center of curvature of the mirror, in which case the object distance (o) is equal to twice the focal length (2f) and the mirror equation becomes 1/o + 1/i = 1/f.

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