Which of the following is heavily doped?

The device used for voltage regulation is

Take the breakdown voltage of the zener diode used in the given circuit as $6\, V$. For the input voltage shown in the figure below, the time variation of the output voltage is: (Graphs drawn are schematic and not to scale)

$A$ Zener diode having a Zener voltage of $8\, V$ and a power dissipation rating of $0.5\, W$ is connected across a potential divider circuit as shown in the diagram. The value of the protective resistance $R_p$ is $....\, \Omega$.

$A$ $9\,V$ stabilized voltage supply is required to run a car stereo system from the car's $12\,V$ battery. $A$ Zener diode with $V_z = 9\,V$ and $P_{max} = 0.27\,W$ is to be used as the voltage regulator. The load resistance is $450\,\Omega$. The value of the series resistor $R_s$ is....$\Omega$.

An ideal Zener diode with a breakdown voltage of $3 \text{ V}$ is reverse-biased with an input voltage $V_i = 5 \text{ V}$. The magnitude of the voltage difference between points $B$ and $A$ is: (in $\text{ V}$)