In a transistor, comparing the doping of emitter, base and collector, the part which is heavily doped and that which is lightly doped are respectively

In the following electrical circuit, the reading in the milliammeter is
(Take knee voltage of silicon diode $= 0.7$ V)

The material used for solar cell should have band gap
(A) equal to zero.
(B) equal to $0.08$ eV.
(C) between $1.0$ eV to $1.8$ eV.
(D) equal to $2$ eV.

For a two input logic gate, when the inputs are 'zero' and 'zero' the output is 'one'. When the inputs are 'one' and 'zero' the output is 'zero'. The type of logic gate is