Problem Set
NBPhO 2025
4. Black Box Exp 12 pts
Determine the internal circuit topology, resistor value, and diode opening voltages of an unknown black box containing three diodes and a resistor.
Tools: a black box with a yellow and a blue lead, two multimeters, a voltage source (that is connected in series with a resistor to limit the maximal current), wires, sheets of graph paper. In the black box, there are three diodes and a resistor.
You are allowed to connect your circuit to the power source only through the yellow lead with a built-in resistor (that is already connected to the power source)!
For each series of measurements, also draw the circuit used!
i) (4 points) Determine the electrical circuit inside the black box.
ii) (2 points) Determine the resistance of the resistor.
iii) (6 points) Determine the opening voltages of all the diodes (at which the current reaches 1 mA).