Electronics > Beginners
How can this be? (picture)
billbyrd1945:
In an effort to learn circuit analysis, I built up this circuit. The math for parallel and/or series circuits agrees with the measured current. I should've stopped there. But I decided to go a step further and measure voltage coming from each resistor using a common ground. Please notice R2 and R3. How can these two resistors pass voltages so different from the others in the circuit? And if R3 is somehow defective, how can R4 inherit the correct voltage. Adding all voltages yields a number greater than the 7.0 set voltage from my power supply. I appreciate any help.
Tom45:
Resistors pass currents, not voltages. Measure the voltages across each resistor, rather than from one side of a resistor to some other point in your circuit.
For example, V1 is voltage across R1, V2 is across R2, etc. You should find that:
V1 + V2 + V5 = 7 volts and V3 + V4 + V5 = 7 volts.
Read up on voltage dividers and then try some simple experiments with 2 resistors in series connected to your 7 volt supply. Once you understand that, you should be able to explain what you are seeing in your example circuit.
ebastler:
When you give this another look, following Tom45's guidance, be sure that you don't confuse yourself with the measurement you have indicated for R5. Your red probe connection for R5 must have been on the bottom side of the resistor, not on the top as drawn.
Doctorandus_P:
Especially when learning electronics, start by learning how to draw schematics properly.
General rules are very simple:
Signals flow from left to right.
Voltages go from top to bottom.
So:
draw your battery / voltage source on the left of your screen.
Then draw 2 horizontal lines. One on the top, that is your "positive voltage rail". and the other on the bottom. That is your "ground"
(These names are arbitrary! but keeping to this convention helps with understanding.
Then connect your voltage source to the 2 horizontal lines.
Then draw your resistors between the 2 voltage rails.
billbyrd1945:
Thanks to all of you. You've given me something to work with. I'll probably post a follow-up image.
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