Solving Electronics Problem: 1N4737 Zener Diode and Radio Circuit

[TyErd]

Homework Statement

A 1N4737 zener diode has a 7.5 V zener voltage and is rated at 1 W power dissipation. It is
to be used in the circuit shown at right to regulate the voltage to a small radio circuit which
requires a constant voltage of 7.5 V. The supply voltage can vary between 9 V and 12 V.

a. What is the maximum current that can pass through the diode without exceeding the
power rating?
b. What is the maximum current that can be drawn by the radio in this circuit?
c. What is the minimum value of the dropping resistor, Rd, that can be used in this circuit?
d. What could happen if a resistor of lower value was used?
e. Why not use a higher value resistor?

I don't get it at all. I need your help!

I understand that part a is simply I=P/V which means current will be 0.13A

Homework Equations

P=VI V=IR P=V^2/R

The Attempt at a Solution

Dont even know where to start with part b.

 

[jbsteele]

Part c, I know V=IR, so the minimum value of Rd would be 7.5V/0.13A = 57.69. Part d, If a resistor of lower value was used, then the current would be higher than 0.13A, thus exceeding the power rating of the diode. For part e, I assume that a higher value resistor would result in a larger voltage drop across the resistor, thus reducing the voltage supplied to the radio circuit.