Flow of electric charge - typically movement of charge carriers, such as electrons. Measured in amperes (A).
Questions tagged [current]
5497 questions
322
votes
6 answers
Choosing power supply, how to get the voltage and current ratings?
Power supplies are available in a wide range of voltage and current ratings. If I have a device that has specific voltage and current ratings, how do those relate to the power ratings I need to specify? What if I don't know the device's specs, but…
Olin Lathrop
- 310,974
- 36
- 428
- 915
173
votes
12 answers
How does the current know how much to flow, before having seen the resistor?
With the following circuits as examples :
and
How will the current I know how much to flow?
Would any other wave travel first in the circuit and then come back
and say so much current should flow?
Prabhanjan Naib
- 1,815
- 2
- 12
- 9
157
votes
4 answers
How can I efficiently drive an LED?
I understand that I can not connect an LED directly to a battery because it will draw too much current. Thus, there must be something else in the circuit to limit the current.
What options are there? Are some methods more efficient than others?
Phil Frost
- 56,804
- 17
- 141
- 262
111
votes
9 answers
Why does a resistor need to be on the anode of an LED?
Please be kind, I am an electronics nub. This is in reference to getting an LED to emit photons.
From what I read (Getting Started in Electronics - Forrest Mims III and Make: Electronics) electrons flow from the more negative side to the more…
Spechal
- 1,213
- 2
- 9
- 6
94
votes
10 answers
How to get more than 100mA from a USB port
I heard that the current limit for a USB port is 100mA. However, I also heard that some devices can get up to 1.8A from a port. How do you get past the 100mA limit?
200ok404notfound
- 1,594
- 3
- 15
- 22
76
votes
10 answers
How much voltage/current is "dangerous"?
Related:
Safe current/voltage limit for human contact?
From what I've heard:
110 V (or 220 V; household voltage pretty much) is dangerous (i.e. can kill you) I think there's consensus on this, no need to try :)
60 V (old telephone lines) is…
user541686
- 1,154
- 4
- 12
- 22
55
votes
7 answers
What is the usage of Zero Ohm & MiliOhm Resistor?
I am new to PCB design and I noticed that some schematics use 0Ω or 100mΩ resistors. What is their purpose and why do we need to use them in our PCB design?
Normally if we wish to probe how much current the load is taking, we put a jumper pin across…
Dennis
- 1,401
- 3
- 17
- 17
48
votes
2 answers
Why don't electrons take the shorter path in coils?
Below is a copper coil, presumably forming an electromagnet. From my understanding the electrons travel around the coil to produce a magnetic field. But why don't the electrons jump the wires and take the shortest path?
Below I tried to draw the…
rrswa
- 627
- 6
- 11
46
votes
6 answers
Why aren’t the main conductors in this underground power cable made from copper?
I’ve found a piece of electrical cable left by the electricity company that supplies the area. They did a repair recently underground.
I’m curious why the three big triangular conductors aren’t made from copper. It looks like aluminium to me, but…
i-CONICA
- 591
- 4
- 6
44
votes
2 answers
Sharp corners in PCB traces
Why does a typical PCB always has rounded tracks? What harm can a sharp edged PCB track can cause? Please explain!
Vinit Shandilya
- 724
- 1
- 8
- 18
44
votes
2 answers
Why do CPUs need so much current?
I know that a simple CPU (like Intel or AMD) can consume 45-140 W and that many CPUs operate at 1.2 V, 1.25 V, etc.
So, assuming a CPU operating at 1.25 V and having TDP of 80 W... it uses 64 Amps (a lot of amps).
Why does a CPU need more than 1 A…
Leonardo Bosquett
- 599
- 1
- 4
- 5
42
votes
10 answers
Is current source also a voltage source?
I'm confused between current and voltage sources; I get the text book definition but I am not able to understand real world difference. To me both current and voltage sources seem as the same. I understand that ideal sources doesn't exist. What is…
user3551094
- 547
- 1
- 6
- 4
40
votes
13 answers
Why can current only flow in loops?
In the following image:
Why can't current flow across the following wire?
It's a simple question, but I've kind off always wondered.
Thanks!
Physco111
- 639
- 1
- 6
- 12
40
votes
12 answers
Is it really OK to supply more current than what the component is rated for?
In this heavily upvoted answer the answerer states that it is okay to supply a component with more current than what it's rated for. The analogy is that (paraphrasing here) "If Johnny wants to eat two apples, he'll only eat two regardless of whether…
Zac
- 615
- 1
- 5
- 6
34
votes
7 answers
When people talk about a device "drawing" current, what do they mean? Why do devices under load "draw" more current?
In my (extremely rudimentary) understanding, the amount of current flowing in a circuit is determined by a) its resistance, and b) the voltage of the power source (voltage from beginning to end), which forces the charge to flow through.
Why then, do…
Chris Cooper
- 443
- 1
- 4
- 8