Name the device 'D' which is used as a voltage regulator in the given circuit . Rewrite the circuit by replacing 'D' with the proper circuit symbol. Give its working principle.

Explanation

D is a zenar diode

Principle : If you increase or decrease the input voltage it results in the increase or decrease in voltage drop across `R_1` but the voltage across the zenar diode remains constant.
`therefore` A constant voltage acts across `R_2`.