Which is the primary constitutional unit for diode and transistor?

Two ammeters $A_1$ and $A_2$ are connected as shown in the given figure. By neglecting the internal resistance of the ammeters, the reading in the meter $A_1$ is (in $\text{A}$)

The circuit contains two diodes,each with a forward resistance of $50\, \Omega$ and an infinite reverse resistance. If the battery voltage is $6\, V$,the current through the $120\, \Omega$ resistance is $mA$.

The cause of the potential barrier in a $p-n$ junction diode is

The dominant mechanisms for motion of charge carriers in forward and reverse biased silicon $P-N$ junctions are

$A$ $2 \text{ V}$ battery is connected to a diode in forward bias. $A$ voltage of $0.5 \text{ V}$ is dropped across the diode,which is independent of the current flowing through it. $A$ current greater than $10 \text{ mA}$ causes excessive heating and damages the diode. If a current of $5 \text{ mA}$ is required in the diode,what value of series resistance must be connected in the circuit?