Question

why is mire than ine image formed in a thick glass mirror

Answer 1

When ever there is a change of refractive index, there will be partial reflection. When a ray enters the glass it goes from air to glass. Therefore there will be reflection. You will see one image. When the light emerges from the glass to air, there is a change of refractive index. There will be one more image. This ray coming from the bottom has a change of refractive index. There will be a partial but faint image. this is not visible in a thin glass. You normally see only two, Other wise we must be able to see infinite number of images.