The conductivity of a semiconductor increases with increase in temperature, because
(a) Number density of free current carries increases
(b) Relaxation time increases
(c) Both number density of carries and relaxation time increase
(d) Number density of carries increases, relaxation time decreases but effect of decrease in relaxation time is much less than increase in number density 

Two 10cm log, straight wires, each carrying a current of 5A are kept parallel to each other. If each wire experienced a force of 10^-5N, then separation between the wires is__________cm.

The positive feedback is required by an amplifier to act an oscillator. The feedback here means:

The variation of acceleration due to gravity (g) with distance (r) from the centre of the earth is correctly represented by: (Given R = radius of earth)

A transistor is used in an amplifier circuit in common emitter mode. If the best current changes by 100 <!-- [if gte mso 9]><xml> </xml><![endif]-->  $\mu A,$ it brings a change of 10 mA is collector current. If the load resistance is 2 $k\Omega$ <!-- [if gte mso 9]><xml> </xml><![endif]--> and input resistance is 1 $k\Omega ,$ <!-- [if gte mso 9]><xml> </xml><![endif]--> the value of power gain is x × 10⁴. The value of x is_____________.

The typical transfer characteristics of a transistor in CE configuration is shown in figure. A load resistor of $2k\Omega$ is connected in the collector branch of the circuit used. The input resistance of the transistor is $0.50k\Omega .$ The voltage gain of the transistor is________.