Question about law of reflection

[sachin123]

When is the law "the image is formed back in the mirror at a distance equal to that of the object from the mirror applicable?

Consider a plane mirror,with a glass slab on it.
Let an object be placed in front of it outside the slab, in air.
Now due to normal shift the mirror will see the object at a distance greater than the actual distance.Now should we use object distance =image distance with this distance,or...

an observer standing near object will see the mirror at a distance closer than it actually is.
Now,should we use object distance = image distance with this distance?

Can someone clear this out for me?I have to use this concept for many problems.
Or how at all should I do problems like this?
Thank You.

 

[cupid.callin]

Consider a plane mirror,with a glass slab on it.
Let an object be placed in front of it outside the slab, in air.
Now due to normal shift the mirror will see the object at a distance greater than the actual distance.Now should we use object distance =image distance with this distance,or...

it will be lesser distance because mostly slabs are denser than air ... it will be greater if slab is rarer than original material (i assumed it to be air)

an observer standing near object will see the mirror at a distance closer than it actually is.
Now,should we use object distance = image distance with this distance?

for mirror both object and image will be at equal distance but for object ... distance from image will not be twice of its distance from mirror

Let original distance is d and shift is x

so object distance from mirror is d-x and also image distance is d-x.

 

[sachin123]

Hey.
So you're saying that we must keep an observer near the mirror and then view the object,and find object distance and blindly use u=v?

Are you sure?
I have heard people argue that that can't be done as the rays after reflection will further get refracted at the slab air interface and this is completely ignored by the method suggested by you.Am i right?

 

[cupid.callin]

the image distance in this kind of questions depends on where is the observer

if observer is b/w mirror and slab then second refraction will have no effect
if he is on left of slab ie towards object then you must consider second refraction