Solving Optics Problem: Position of Image of Face Due to Reflection

In summary, the problem involves finding the position of the image of a face reflected in a bathroom mirror with a glass sheet of thickness d and index of refraction n. For part a, the image is located a distance of h behind the glass, and for part b, the image is located at a distance of h+2d/n. Additional equations and calculations are needed to find the position for part b, taking into account the effects of refraction at the glass-air interface.
  • #1
EngageEngage
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Homework Statement


Consider a bathroom mirror with a glass sheet of thickness d and an index of refraction n. Your face is located at a distance h from the front surface of the galss sheet. a
a. find the position of the image of your face that you see due to the reflection from the front surface of the glass
b. find the position of the image of your face that you see due to the reflection from the mirror surface behind the glass. Take into accound the effects of refraction at the glass-air interface.


Homework Equations


na/s + nb/s' = (nb - na)/R
1/s + 1/s' = 1/f


The Attempt at a Solution


for part a, we know that the image is a distance of h behind the glass, thus s' = -h. However, I'm not sure what to do for the second part.
the answer to part b is h+2d/n, but I'm not sure how to get there. If someone could help me that would be much appreciated. Thank you
 
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  • #2
I tried to do something else and I got close to the answer, but still not it:

first i did:

1/h+ n/s' = 0 (because R --> infinity for plane mirror)
s' = -nh
then I took the distance from the surface of the mirror to the glass, d, and subtracted s' from it to find the object distance for the mirror:

s2 = d+nh.
After reflection, we have s2' = -d-nh. Then using the 'relevant equation' to find the final image, i get

n/(-d-nh) =-1/(finalim)

final I am = (d+nh)/n => d/n + h.

So, I am off by a factor of two on the (d/n) term. I'm not sure what it is that I'm doing wrong. if someone could please help me out, that would be much appreciated.
 
  • #3
.

To solve part b, we can use the refraction equation, which relates the angles of incidence and refraction at an interface between two different media. In this case, we have air and glass, so the equation becomes:

n_air * sin(theta_air) = n_glass * sin(theta_glass)

Where n_air and n_glass are the refractive indices of air and glass, respectively, and theta_air and theta_glass are the angles of incidence and refraction, respectively.

Since we are interested in the position of the image of our face, we can use the thin lens equation, which relates the object distance (h) and image distance (s') to the focal length (f) of the lens:

1/h + 1/s' = 1/f

Combining these equations, we can solve for the image distance (s'):

1/h + 1/s' = 1/f
1/h + 1/(h+2d) = 1/f
1/(h+2d) = 1/f - 1/h
1/(h+2d) = (h-f)/(hf)
(h+2d)/(h-f) = hf
s' = (h+2d)[(hf)/(h-f)]

Therefore, the position of the image of our face due to the reflection from the mirror surface behind the glass is (h+2d)[(hf)/(h-f)].

I hope this helps. Let me know if you have any other questions.
 

Related to Solving Optics Problem: Position of Image of Face Due to Reflection

1. How do I determine the position of the image of a face due to reflection?

The position of the image of a face due to reflection can be determined using the law of reflection, which states that the angle of incidence is equal to the angle of reflection. You will also need to know the distance between the face and the reflecting surface, as well as the refractive index of the medium between the face and the surface.

2. What is the law of reflection?

The law of reflection is a fundamental principle in optics that describes the behavior of light when it reflects off a surface. It states that the angle of incidence, measured from the incoming light ray to the normal (perpendicular) line of the reflecting surface, is equal to the angle of reflection, measured from the reflected ray to the normal line.

3. How does the distance between the face and the reflecting surface affect the position of the image?

The distance between the face and the reflecting surface plays a crucial role in determining the position of the image. The farther the face is from the reflecting surface, the larger the angle of incidence and therefore, the larger the angle of reflection. This results in a larger displacement of the image from its original position.

4. What is the refractive index and how does it affect the position of the image?

The refractive index is a measure of how much a material can bend light. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the material. The higher the refractive index, the more the light will bend when passing through the medium, which will affect the position of the image.

5. Can the position of the image be calculated for any reflecting surface?

Yes, the position of the image can be calculated for any reflecting surface as long as the necessary information, such as the distance between the face and the surface and the refractive index of the medium, is available. However, the accuracy of the calculation may vary depending on the complexity of the reflecting surface and the angles at which the light is reflecting.

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