Two lenses, one concave and other convex, of focal lengths $-20$cm and $40$cm$,$ respectively are separated by distance d$.$ Determine the value of d for which the system acts like an ordinary glass plate $($i$.$e$.,$ a parallel beam incident on the left side emerges as a parallel beam on the 

right side.

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The system acting like an ordinary glass plate implies that the combination of the two lenses doesnt ... View the full answer