it's virtual since it cannot be projected on a screen since it is just like you are using a mirror. it is formed by the total internal reflection of two glass prisms...each glass prism has a critical angle of 42 degrees and all light rays hit its surface at 45 degrees so it is reflected by 45 degrees. so the rays get reflected twice like this and so turn 90 degrees twice. thus they are upside down.HELP IS NEEDED
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w06_qp_6.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w06_ms_3.pdf
q 6 b) how is it virtual no lines r extended??????????? and why is it inverted???????