How second image is brightest here? One of my Textbook's Multiple Choice Question is- 
A Thick plane mirror shows a number of images of the filament of an electric bulb. Of these, the brightest image is the-


*

*First

*Second

*Last

*Fourth


First of all I fail to understand How can a single plane mirror forms some number of images ??It should form only one. 
According to me the answer should be either all of them are equally bright or the first one (Logically due to reflection, brightness might decrease)
But Answer given in my textbook is 2.Second
 A: The mirror described in the problem sounds like one used in a bathroom: a slab of glass with a silver coating on the back (see diagram below). This means that the first reflection is off the front of the mirror, which is a reflection off glass. The second reflection will be off the silver backing. Silver is much more reflective than glass, which makes sense, as glass is supposed to be transparent.
Incoming    / First reflection
    \      /
     \    /       / Second reflection
      \  /       /
       \/       /        Air
     ---\------/-----------
         \    /
          \  /           Glass
           \/
     ===================== Silver coating

The third image would come from the light bouncing off the front surface of the glass and then a second time off the silver backing.
As a side note, mirrors designed for scientific use, like telescopes, are silver-coated on the front to avoid exactly this problem of multiple reflections.
A: This is because it suffers a strong reflection at the silvered surface.
