If the figure shown are 2 LED's that can be used as a polarity detector. Apply a positive source voltage and a green light results. Negative supplies result in a red light. Packages of such combination are commercially available. Find the limiting value of the resistance of resistor R to ensure a current of 20 mA through the ON diode for the configuration. Both diodes have reverse breakdown voltage of 3V and effective turn on voltage of 2V. (Consider ideal behaviour of diodes)