With the red lead in the V/Omega port and the black lead in the COM port, I can measure:
Continuity: to check if energy flows continuously through an electrical component (dial set to the Continuity Test Mode)
Resistance: to check the value of my resistors (dial set to Omega for Ohms)
Voltage: the potential difference in electrical energy between two points in a circuit (dial set to DC Voltage)
Here is my circuit: one LED with a 220 Ohm resistor powered by my Arduino, which is connected to my laptop via USB. I expect the board to be receiving 5V from the Arduino (notice the red lead all the way on the left connected to the 5V pin).
I decided to measure the voltage of the entire circuit, first. I set my multimeter to DC Voltage 20V (because I'm expecting a reading lower than this of ~5V), and keeping the leads in parallel with the circuit, placed the tip of red lead at the red wire feeding the LED the current and the black lead on the resistor wire headed towards Ground. for a reading of 4.88V.
I then measured the voltage across the resistor for a reading of 1.88V
Finally, I measured across the LED, with the red lead on the anode and the black lead on the cathode for a reading of 2.97V. This, combined with the voltage across resistor, gives a total of 4.85V. Pretty close to 5V! I want the voltage used up in a circuit. If not for the resistor in this circuit, the LED would received too much power and burn out.
Here I've added a switch to the circuit. A voltage reading returned a zero when the switch was both open and closed, however my multimeter beeped when I checked the switch for continuity. In this image the switch is unpressed and open, and the voltage readings across both the resistor and the LED were zero.
Even with the button pressed and the circuit closed, the voltage readings across the resistor and the LED were roughly identical to the practice above, 1.88V and 2.96V respectively for a total of 4.84V.
Now I've added another LED in series to the circuit.
With switch closed, voltage across the resistor measured at 1.29V, across the first LED at 1.78V, and across the second LED at 1.77V, for a total of 4.84V. Again, all the voltage is used up, even with the addition of the third component.
Changing the color of the second LED also slightly impacted the measurements: resistor (1.18V), red LED (1.77 ), and yellow LED (1.88V).
Adding a third LED to the circuit, also in series, and nothing lights up. All three together need more power than 5V from the Arduino can supply.
The circuit is now set with three LEDs in parallel to one another. When I measured the voltage across each, I received identical readings of 1.75V.
In order to measure the current through the circuit, I adjust my multimeter as seen here and dialed to DC Amperage 20mA (as again I was expecting a lower below this upper limit).
Curious, I decided to measure the current with just one LED first. With my multimeter in series with the circuit, I disconnected the LED's cathode from the breadboard, touched it to my red lead--a point of higher voltage in the circuit, and set the black lead at a point of lower voltage--the disconnected leg of the resistor. I completed the circuit with my multimeter and received a reading of 13.07mA.
Back in parallel with one another, I disconnected the cathode of each LED, and with the button pressed, used my multimeter to complete the circuit: LED A 3.28mA, LED B 3.38mA, and LED C 3.73mA. The total amperage drawn by the three was 10.39mA. Why a 3mA difference from the measurement with just one LED?
Here I've created a circuit with a potentiometer, which is a variable resistor or voltage divider. My voltage readings when the pot was dialed all the way towards power (and the light beaming bright!) were pot powered terminal to wiper 0, wiper to GND terminal 4.91V, 2.95V across the resistor, and 1.89V across the LED.
When the pot dial was ~midway (and the light dimmed): pot power terminal to wiper 2.57V, 0.59V across the resistor, and 1.73V across the LED.
With the pot dial all the way towards ground (and no light): pot power terminal to wiper 4.91V, 0V across the resistor, and 0V across the LED.