In the circuit shown, a 5V Zener diode is used to regulate the voltage across load . The input is an unregulated DC voltage with a minimum value of 6V and a maximum value of 8V. The value of  is 6Ω. The Zener diode has a maximum rated power dissipation of 2.5 W, Assuming the Zener diode to be ideal, the minimum value of  is ___________ Ω. 

The sinusoidal ac source in the figure has an RMS value of . Considering all possible values of , the minimum value of  in 3 to avoid burnout of the Zener diode is __________.

In the circuit shown below, the knee current of the ideal Zener diode is 10mA. To maintain 5 V across , in Ω and the minimum power rating of the Zener diode in mW respectively are         

The current through the Zener diode in figure is

Figure shows an electric voltage regulator. The zener diode may be assumed to require a minimum current of 25 mA for satisfactory operations. The value of R required for satisfactory voltage regulation of the circuit is