LED Currents

Project Number: 30

Description: Build the circuit, set the slide switch (S5) to position B, and set the meter (M6) to the 0.5mA setting. This circuit has the LED in series with a 10K ohm resistor in the pivot stand. 10K ohm is a high resistance, so the meter measures a small current and the red LED (D1) is dimly lit. It is easier to see the red LED if you take the circuit to a dark room. If the LED does not light at all, then the battery needs to be recharged. Switch the meter to the 50mA setting. Now set the switch to position C, replacing the 10K ohm resistor with a smaller 47 ohm resistor in the pivot stand. The LED is brighter now and the current is higher. Now push the press switch to bypass the 47 ohm resistor. The current and LED brightness are even higher now. Replace the red LED with the yellow LED (D5) and see how the brightness and current change.

Snappy: Adding resistors to a circuit is like partially blocking a water pipe, reducing the flow of water. High currents can damage LEDs, so resistors are usually used with them to limit the current. Your D1 and D5 LEDs have internal resistors of around 50 ohm to protect them.