100 votes
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Why can current only flow in loops?

What you have to understand is that electrons don't move on their own but as a chain... like a bunch of kindergarten kids tied together hand in hand. Consider the following drawing of a series of ...
Trevor_G's user avatar
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80 votes
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Why is the time constant 63.2% and not 50% or 70%?

Other answers haven't yet hit upon what makes e special: defining the time constant as the time required for something to drop by a factor of e means that at any moment of time, the rate of change ...
supercat's user avatar
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74 votes

Saving data without a microcontroller?

You can't use a EEPROM or any other storage means that is digital without first converting your signal to digital. Using a microcontroller is the obvious and simple way to do that. However, if you ...
Olin Lathrop's user avatar
72 votes
Accepted

If a circuit only has a current source and no voltage source where does the voltage come from to supply the circuit?

An Ideal current source will produce whatever voltage is necessary to permit it to deliver its specified current. An ideal voltage source will deliver whatever current the rest of the circuit ...
Peter Bennett's user avatar
58 votes
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Why is root mean square used when calculating average power, and not simply the average of voltage/current?

Take a simple example where the sums are trivial. I have a voltage that is on 50% of the time and off 50% of the time. It is 10V when it is on. The average voltage is thus 5V. If I connect a resistor ...
Spehro Pefhany's user avatar
58 votes
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Is Ohm's law really accurate?

Ohm's Law says that the current through a resistance is the voltage across it divided by the resistance. The key point is that it is the voltage across the resistance, not the voltage of your supply, ...
GodJihyo's user avatar
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55 votes
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Why would a circuit designer use parallel resistors?

Power dissipation will be the driver. Using six in parallel allows use of standard resistors which may be a stock item. Using standard parts allows use of automatic assembly equipment. Lower profile. ...
Transistor's user avatar
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51 votes
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Shocked by beginner circuit kit

OK. You say that it was a single jolt, and you pulled your hand away immediately. It was one of two things -- either it was static discharge and a true shock, but exactly what you would have gotten ...
TimWescott's user avatar
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50 votes
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What is the true circuit behind an opamp?

Here is a $35 kit you can make, which ends up being the equivalent of a 741 op-amp using discrete 13 2N3904 and 7 2N3906 transistors. It has eight binding posts representing the eight pins of the ...
tcrosley's user avatar
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50 votes

Why is the time constant 63.2% and not 50% or 70%?

It's built into the mathematics of exponential decay associated with first-order systems. If the response starts at unity at t=0, then after one "unit of time", the response is \$e^{-1} = 0.36788\$. ...
Dave Tweed's user avatar
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45 votes

An intuitive interpretation of Negative voltage

You could consider the voltage a bit like floors on a building. A numbering system used in many places in Europe defines that the ground floor is 0 or G, that floors above it are numbered positively ...
Transistor's user avatar
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44 votes
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The Intuition for RLC circuits

[!Quote] by a ConcernedCitizen Resistors are the electrical equivalent of friction and produce losses to remove energy from the system. If you drop a frictionless pendulum to swing it, how long does ...
DKNguyen's user avatar
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44 votes

Not understanding why these two resistors are in parallel

It is entirely equivalent to the other answers, but sometimes it helps visualising to compress each connected segment down into a single node, as in the following diagram. I imagine lengths of solder,...
jonathanjo's user avatar
42 votes
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What are the various 'properties' of a diode?

DC Level 0 Diode The level-0 approximation of a diode is simply an assumed voltage drop across it when forward-based and infinite impedance when reverse-biased. When reverse-biased, no amount of ...
jonk's user avatar
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38 votes

Why can I use P = I²R but not P=V²/R when calculating energy lost in a circuit?

The problem assumes you understand something that is not clearly spelled out: the wires and the (unknown) load are in series. Therefore they share the current, not the voltage of the battery. That's ...
LorenzoDonati4Ukraine-OnStrike's user avatar
37 votes

Saving data without a microcontroller?

No, you can't store an analog value as-is on a digital storage medium like an eeprom or an SD card. You could do an analog-to-digital conversion (using an appropriate chip) to convert your analog to ...
Wouter van Ooijen's user avatar
36 votes
Accepted

What does this transistor circuit do?

The circuit topology is that of a capacitance multiplier designed to remove ripple from a 'dirty' regulated power supply. The name stems from the fact that the value of the capacitance seen from the ...
Sredni Vashtar's user avatar
35 votes
Accepted

What is the use of an op-amp whose output and inverting input are connected to ground?

The first OP-amp is actually creating the circuit ground. The 7810 creates a stable 10 volt, which is then divided by the voltage divider R2 and R3, filtered by C3 to make a stable 5 volt level ...
pipe's user avatar
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35 votes

Why is root mean square used when calculating average power, and not simply the average of voltage/current?

For power to be average i must be average current, so I am surmising that the effective current is the average current. In short, average voltage x average current only equals average power when ...
Andy aka's user avatar
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35 votes
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Why can I use P = I²R but not P=V²/R when calculating energy lost in a circuit?

60A through a 0.01ohm resistance gives a 600mV drop. That is the voltage you need to use in the equation.
Ignacio Vazquez-Abrams's user avatar
35 votes

How to compensate noise at the output of logic gates?

They are not noisy. They are responding to the signals you have delayed through U9 to U12. Combinatorial logic responds after a short delay to any change on its input. If closely spaced changes occur, ...
Neil_UK's user avatar
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32 votes

What is the use of an op-amp whose output and inverting input are connected to ground?

While I agree with @pipe and in fact upvoted his answer, an additional nuanced reply is that a ground is more than "just" a reference. What I mean by this is a ground is not just a voltage, but ...
placeholder's user avatar
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30 votes

Why can current only flow in loops?

There is a more mathematical and precise answer than those above, and it turns out to be one of the more interesting and important concepts in electromagnetism. First, what does it mean "current ...
Evan's user avatar
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29 votes

Is Ohm's law really accurate?

All models are wrong. Some models are useful. First, you should calculate the resistance of the wires (Whether thick or thin) and include that in your model. Provided the thin wire isn't too thin, the ...
The Photon's user avatar
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29 votes

Reasons to use combinations of resistors (parallel or in series): Looking for educational examples

Examples from the real world: Sticking to the "E series". The calculated component value you need might not be available in one of the standard "E series", which in turn means ...
Lundin's user avatar
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28 votes
Accepted

How to solve resistance in this circuit?

I find for some students, the angled components are visually confusing. Try redrawing the same schematic with only horizontal and vertical components to see if this helps you to analyze it. For ...
Glenn W9IQ's user avatar
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28 votes
Accepted

Why do I need a ground when simulating a circuit? I thought voltage was relative between two nodes!

You are absolutely correct: Voltage is only defined between two nodes. In many electronic circuits there is a constant-voltage* power supply that connects to many parts of the circuit. By ...
Solomon Slow's user avatar
  • 3,103
28 votes

Why exactly does maximum power transfer happen at 50 ohms (matched impedance)?

The power delivered to the load is from the Joule heating effect: \begin{equation} P=\dfrac{\Big(\dfrac{R_L}{R_L + 50}G\,V_{IN}\Big)^{2}}{R_L} \end{equation} So from differential calculus we know ...
Iron Maiden's user avatar
  • 1,214
27 votes
Accepted

Can anyone identify this circut?

If you sum the capacitors to just one, then it looks like an envelope detector. If you put capacitors in parallel then you can sum them together to just one. $$C_{tot}=C_1+C_2+C_3+C_4$$ And then you ...
Harry Svensson's user avatar
27 votes

Can we ground all the nets in a printed circuit board?

You will need to check the datasheets for each part with unused pins. In many cases grounding them is a BAD idea, though in many other cases it may be CRUCIAL. And in some cases you SHOULD leave the ...
DerStrom8's user avatar
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