Diodes

A semiconductor diode, or a p-n junction diode, looks similar to a resistor, but act very differently. It has a band at one end, which marks the n-side of the p-n junction. The symbol points in the direction that conventional (positive) current would flow.

1. Connect the diode in these two ways.

c. Which acts like an open switch and which acts like a closed switch?

d. For each measure:

• the potential difference across the 1000 W resistor, VR

• the potential difference across the diode, V_D.

e. Calculate the current, I. If the current seems to be almost zero, measure it with an ammeter.

f. Calculate the resistance of the diode, R_D.

g. Write the resistance of the diode(R_D) in terms of V_D, V_R, and R.

h. Check your results with a different resistor. Using a smaller R, causes R_D to increase or decrease? 2. Now use a light-emitting diode, LED, to replace the diode in the above circuit. Be sure to adjust the resistor, so that the current through the LED is about 20mA.

a. Does the LED light up when it is forward or reverse biased?

b. What do you see as possible uses for diodes?

c. What do you see as possible uses for LEDs?