Mammoth Memory

Flat mirrors – Who can see whom – People random

In the following diagram you may be asked in an exam who can see whom. If A, B, C and D represent people standing randomly looking at the mirror, who would each person see?

Random group of people looking in a mirror

To work out who can see whom just apply the laws of reflection from each person's perspective to each of the others'.

The first stage is to draw an image on the other side of the mirror perpendicular (at 90°) to the mirror.

Behind the mirror equal distance same size

1st stage of drawing a ray diagram of random people looking in a mirror

We end up with a diagram as follows:

Images random people see in a mirror

The second stage is to draw rays to person A from each of the other images of people.

We can also complete the third stage by joining the light rays from the mirror to the other people as follows:

2nd stage of drawing a ray diagram of random people looking in a mirror

Person A can only see person D.

 

We can now repeat the process for person B.

Ray diagram showing who person B can see in the mirror

Person B can see person C and person D though the mirror.

 

Now let's try person C

Ray diagram of what person C can see in the mirror

Person C can see person B, themselves and person D through the mirror.

 

Finally, let's find out who person D can see.

Ray diagram showing what person D can see in the mirror

Person D can see everyone including themselves.

 

Summary

       Person Can see  
  A D  
  B C, D  
  C B, D and themselves  
  D A, B, C and themselves  

 

 

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