# Questions tagged [basic]

Fundamentals of electricity, electronics, components, or theory

51 questions
7k views

### What is an amp (and other such basic questions) in the simplest possible terms?

I understand that this is a really basic question, but, I've been unable to really understand electrical terminology for some reason. What exactly is an amp? How does it correspond to a watt? And: ...
2k views

### Do electrical devices “take what they need”

One concept of electronics I have a hard time understanding is if things like motors, actuators, solenoids etc. use as much power as they need or what you give them. If a motor needs 12 volts and ...
4k views

### Basic rules to calculate the equivalent resistance of a resistor circuit

I have a certain circuit only containing resistors of different values. There is one 'input' and one 'output' for the current. How do I calculate the equivalent resistance of the circuit? Are there ...
6k views

### Basic operation of a bipolar junction transistor

I've tried really hard to understand the basic operational principle of a transistor. I've referred to many books and been to forums but have never got a convincing answer. Here are the things I want ...
5k views

### What is a Charge?

I'm a high school student. I love computers and electronics. Few weeks ago, I thought to build my own electronic gadget but, unfortunately I had not much knowledge in electronics. So, I decided to ...
771 views

### Basic voltage divider issue in my amateur circuit XBee

Once again I need your help in my project. I have a 4,5v powered circuit. I put a voltage divider with 2 resistors in series to reduce my initial voltage of 4.5 V to 3.4 V (to feed an XBee module). ...
6k views

### Can a circuit be powered from Earth with a return ground on Mars?

Could you use a hot wire (120v 60 hz) from earth and a copper rod inserted into another extraterrestial body (mars) to complete a circuit? If impedance wasn't something to worry about (pretend Mars is ...
4k views

I'm a computer scientist with zero exposure to things directly related to hardware (barring what I learned from my undergrad computer org class.) I've been very attracted to the field of embedded ...
32k views

### How do I connect two identical batteries to increase the consumer lifetime?

If I've got a device that uses a single battery, and with that single battery, the device lasts an hour, and I want the device to last for two hours, I'm assuming I can wire two batteries up and it ...
4k views

### How to electronically generate exponential and logarithmic functions

i mean, it is possible to generate with Op amps, or diodes, etc, to generate complex exponential and logarithmic functions, like one can create sinusoidal signals using a Wien bridge oscillator. ...
2k views

### “A zener with series diode”?

So I'm still reading The Art of Electronics Third Edition. On P.39, when dealing with indicative "kick", I found this sentence: For the fastest decay with a given maximum voltage, a zener with ...
4k views

### What operation could cause the inductor or the capacitor to explode?

In really early days of electronic school, the teacher used to say something about not unplug power too quickly at an inductor or capacitor and we were used to slowly turn the voltage generator from a ...
30k views

### How does an astable multivibrator LED blinking circuit work?

I am a beginner in electronics. I come to know about the oscillator using RC circuits (capacitor charge and discharge and time constant tells the behavior of circuit). Then I saw the following ...
27k views

### How can voltage burn out an LED?

I understand how a current higher than what the LED is rated for can burn out an LED, but how does something equivalent happen with voltage? If the correct current is on an LED but the voltage is too ...
11k views

### 555 timer: how to set values to take an hour

I'm new (and novice) in electronics. I came to seek your knowledge to see if someone can help me with a very basic circuit. It is a 555 chip, which should light a LED (for about 1/2 second) every ...
4k views

### How can I create an SCR using a PNP and NPN?

Several times I have seen an SCR described as similar to a PNP and NPN transistor linked together. But any attempt to replicate the idea seems to fail. In the circuit below, for example, the LED is ...
2k views

### Decrease in stored energy after connection of another capacitor

A 3-µF capacitor charged to 100V is connected across an uncharged 6-µF capacitor. So the initial stored energy is: 15mJ and the final: 5mJ. What happen to the 10-mJ of energy?
5k views

### Double-Subscript Notation for Voltages

I have read from some book that: "The voltage quantity symbol V sometimes has subscripts to designate the two points to which the voltage corresponds. If the letter a designates one point and b the ...
221 views

### Where do these grounding wires go? [duplicate]

In the following schematic the two Vss pins where are supposed to be the grounding pins don't connect to anything. Does this mean that the circuit is self-grounding (if that's even a thing)? I'm ...
1k views

### why electricity requires a closed loop to flow?

Imagine a battery with the positive terminal connected to ground. The positive side has a high eletrical potential, ground obviously has a lower electric potential. Electricity wants to seek a lower ...
2k views

### How can I find maximum power transfer using Thevenin equivalent

As I understand it, should maximum power transfer be when $$R_L=R_{th}$$ then $$P_L= P_{L(max)}$$ So that this should do the trick: $$P_{L}=\frac{V_{th} ^2}{R_{th}}$$ But it seems that I am ...
10k views

### When does the placement of a resistor matter?

I've been a programmer for years but am very new to electronic engineering. So far I see people saying it doesn't matter where a resistor goes in your LED circuit as long as it is present, but it ...
633 views

### What's the rationale behind these warnings about extension cords?

(Disclaimer: I've read the help center and I do understand that this is bordering on off-topic since it's about consumer devices. However I hope that I've managed to make enough on-topic by asking ...
3k views

### Triode - how come grid is “more negative” than cathode?

This is probably the most lame question of all the time here, but... I cannot understad grid-cathode "negative" polarization. For me, grid is always positive to the cathode. I mean, in practice, ...
2k views

### wattmeter average power

Average power can be measured by wattmeter, so why in the attached example it doesn't function properly- doesn't show 0 W?
2k views

### If Conventional Current is wrong, how can I trace the flow of current in a schematic?

If Conventional Current is backwards, how do I look at something like this schematic and trace the flow of current? I'd like to follow the design linearly from positive to negative. When the battery ...
32k views

### How can I learn electronics at home? [duplicate]

Possible Duplicate: Learning about electronics I am 40. I am an architect by profession. I am very interested in learning electronics. I don't have time to go to college for an electronics ...
37k views

### Connecting a potentiometer

I know how to connect potentiometer, but to be honest I don't know why. I would really like to understand what I'm doing. From what I have read the input voltage and the ground should be connected ...
8k views

### Why does isolation transformer protect from shock?

Perhaps I can best explain the question with two examples: (1) there is PC powered directly from 230V mains (unprotected by RCD or similar), and there is fault in PC that causes line voltage to ...
11k views

### What is the voltage divider rule?

Can anyone explain what the voltage divider rule is? How has the author of this book used it for analyzing the Voltage Divider Bias circuit for transistors? And can anyone explain how the two ...
808 views

### Why does oscilloscope show large amplitude when I touch the probe?

When I touch the probe I see a 50Hz sine wave with an amplitude of about 100V from peak to peak. I understand that 50Hz is the mains hum picked up through my body, which acts as an antenna, but where ...
53k views

### Why should a circuit be grounded?

Why should a transistor circuit be grounded? The way I understand it is that ground is an infinite supply of electrons and so it is equivalent to the negative terminal of a battery. But in this page , ...
537 views

### Confusion about what should be a simple resistor-divider circuit

I'm reverse engineering a circuit in some industrial equipment, and I came across some curious behavior of the input circuit... The circuit is pretty simple, it is a resistor divider with a capacitor ...
268 views

### Understanding this LPF in opamp feedback loop

I'm using a basic opamp driven mosfet to implement a precision low current sink for an LED: This seems to work just fine within the range that I want it (10mA or so). I've seen other circuits that ...
2k views

### Voltage across Capacitor and Inductor with DC Voltage and Current source

As we know, capacitors and inductors are most important components in circuit design. I am just curious about how they will behave when connected across voltage or current source as per below image ...
1k views

### Fundamental question about circuits and grounding

I understand that voltage is relative and that the hot wire in house mains is a nominal $\pm$ 120v in reference to the neutral wire. I also believe the ground wire is connected to the neutral at the ...
10k views

### Why is the Ampere the only SI fundamental unit for electricity?

According to wikipedia the only SI fundamental unit for Matters Electrickal is the ampere. Don't you at least need the ohm to derive anything? How would you make volts from only amps? Perhaps I ...
453 views

### Grounding in circuit diagrams

Often I see in circuit diagrams that the circuit is connected to the ground: I understand that this creates a reference for zero potential, but why does all of the current not simply flow right into ...
264 views

### How can you build a floating two-port VCVS?

I have a control voltage at one point in a circuit which I need to duplicate at various other points (3 or 4, if I remember correctly). I'd like to use one potentiometer to control these voltages, so ...
2k views

### Conditions for Thevenin and Norton non-existance

It's not clear to me when a Thevenin or Norton equivalent cannot be produced for a given linear circuit. Can anyone help me with a clear definition? Thanks!!
1k views

### In an op-amp, why does Vn approach Vp until the difference is delta V / A? Why doesn't Vn just equal Vp?

In an op-amp (non-inverting), when $V_s$ increases by $\Delta V$, $V_n$ approaches $V_p$ until the difference is $\Delta V/ A$ (where A is infinity). Why is there the $\Delta V/ A$ ...
1k views

### L7809CV increasing voltage from 3V to 9V

I just got a voltage regulator and I was playing with it in a simple DC circuit. My Source is 3.25V, the OUT pin on the voltage regulator (L7809CV) shows 2.25. My confusion starts with the 1V drop in ...
377 views

### How bad can an unconnected ground be?

My collegue here has two seperate boards linked by an SPI link. He just asked me: "So... you need to connect the grounds?" After I picked myself off the floor and answered very much in the affirmative,...
325 views

### Source follower basic question

I just want to clear my understanding about a basic source follower circuit. Following is the circuit Here is my question: Considering Vi > Vgs(th); Vo = Vi - Vgs. Also Vo = Id*Rs as shown in the ...
592 views

### Replacing BJTs with power MOSFET

I have 2 x 2N2222 BJTs powering 2 relays of 200mA each. I am using 2 output pins with 500ohm resistors to power the transistors. After powering it the circuit not working well, while replacing the ...
84 views

### Is it really problem if 0,3 voltage more than required applied in digital multimeter?

Does it negatively affect if more 0,3v voltage than Power Supply (PS) required by general digital multimeter (DMM) supplied ?. I have a DMM with PS requirement of 2 x 1.5v AA battery and in hand is 2 ...
357 views

### Basic Capacitor Discharge [closed]

I found this illustration from the SparkFun website on how a capacitor charges and discharges, but I have some difficulties with it (and capacitors in general): What initially causes the capacitor to ...
587 views

### Sensing a touch of a metal

Assume there is a piece of metal. I would like to identify, with a microcontroller, if another metallic object is touching this piece. I want to apply this for a smart hook that "knows" if a ...