Physics
A simple microscope consists of :

A long focus convex lens
A short focus concave lens
A short focus convex lens
A long focus concave lens

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Physics
In a bipolar junction transistor

The base has the least concentration of impurity
The emitter has the least concentration of impurity
All the three regions (the emitter, the base and the collector) have equal concentrations of impurity
The collector has the least concentration of impurity

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