Why are elemental dopants for Silicon or Germanium usually chosen from group XIII or group XV?

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________.