71.

In a common-emitter amplifier, the load resistance of the output circuit is 1000 times the resistance of the input circuit. If α = 0.98, then voltage gain is

• 49 × 10³

• 2.5 × 10²

• 1.5 × 10²

• 4.9

The plane faces of two identical plano-convex lenses each having a focal length of 50 cm are placed against each other to form a usual biconvex lens. The distance from this lens combination at which an object must be placed to obtain a real, inverted image which has the same size as the object is

• 50 cm

• 25 cm

• 100 cm

• 40 cm