All Questions
173 questions
21
votes
8
answers
14k
views
Why do we reduce only current to prevent power loss? Why not voltage?
In power transmission lines current is kept low and voltage is kept high to reduce the power loss. This is because $P = I^{2}R$ and $P = VI$. In order to reduce power loss we have to reduce $I$ since $...
- 335
20
votes
4
answers
5k
views
Are the "bird sitting on a live wire" answers wrong?
Long ago, my high school teacher wrote the popular question on board,
"Why doesn't a bird sitting on a live wire get electrocuted?"
He gave us four options (I don't remember all of them) ...
- 1,461
16
votes
3
answers
122k
views
Why do birds sitting on electric wires not get shocked?
When we touch electric wires, we get shocked. Why don't birds sitting on electric wires not get shocked?
14
votes
4
answers
27k
views
How can one derive Ohm's Law? [duplicate]
I am looking for the derivation of Ohm's Law, i.e., $V$ is directly proportional to $I$. Can someone help me with it?
- 559
14
votes
8
answers
110k
views
What causes an electric shock - Current or Voltage?
Though voltage and current are two interdependent physical quantity, I would like to know what gives more "shock" to a person - Voltage or Current? In simple words, will it cause more "electric - ...
- 157
13
votes
7
answers
6k
views
Why it is more dangerous to touch a high voltage line wire where current is actually less than households?
I have seen that power is transmitted from power stations to households at high voltage and low current to minimize the power loss.
That means the current in the transmission line is less than the ...
- 356
13
votes
5
answers
4k
views
Watts vs. volts amperes
What I understand:
In simple DC circuits, this is a product of the current and voltage, such that 1 watt = 1 ampere x 1 volt
I understand that a watt is a unit of power (change in energy per unit ...
- 329
12
votes
2
answers
2k
views
Which electrons kill you during electrocution?
I understand that there are three velocities in play in a circuit (I haven't studied Physics past high school so give me some rope)
v1: the velocity by which the electrical field propagates through ...
11
votes
7
answers
21k
views
Difference between current and voltage sources
I am confused about the current and voltage. My intuitive example would be that of a pipe of say water. The diameter of the pipe determines the amount of water flowing per second but the pressure is ...
- 211
11
votes
1
answer
2k
views
High voltage power lines - clarification of energy loss
I've been having a bit of trouble understanding the high-voltage power lines. If I was sending power from $A \rightarrow B$, we have:
Ohm's law $V = IR$
Power lost in the form of heat $P = I^2 R$
...
- 914
11
votes
3
answers
5k
views
Why high voltage transmission lines?
This is a question which I seem to have tackled multiple times, solved each time after reading a dodgy internet explanation, then partially forgotten about and retackled half a year later. It is time ...
- 7,030
10
votes
9
answers
4k
views
How does the current remain the same in a circuit? [duplicate]
I understand when we say current, we mean charge (protons/electrons) passing past a point per second. And the charges have energy due to the e.m.f. of the power supply.
Now tell me, if a lamp has ...
- 350
10
votes
3
answers
2k
views
Does an electric current flow in an open circuit?
When the positive and negative terminals of a battery is connected through a wire, an electric current flows across the circuit. Generally, electrons are the ones that flow (from negative terminal to ...
- 167
10
votes
2
answers
75k
views
How can be the neutral wire at 0 volts when current flowing through it?
Voltage is potential difference, and current flows because of voltage. So if the voltage is zero, how can current flow through the neutral wire.
- 181
9
votes
5
answers
4k
views
How does the electrical ground rod work?
I was reading this article about shock current path, but it seems to be contradicting answers that I have seen on this site regarding electric shock. I can't find the original question but it was ...
- 275
9
votes
5
answers
4k
views
Why is it easier to raise AC current to high voltage than DC?
In my country (and maybe all around the world I don't know) once electricity has been generated, it is then raised to 200k Volts for transportation.
I know this is to reduce the loss. Given $P=U.I$ ...
- 201
9
votes
3
answers
8k
views
When the voltage is increased does the speed of electrons increase or does the electron density increase?
I am just a high school student trying to self study, please excuse me if this question sounds silly to you.
I know that current is a product of the speed of electrons and the electron density.When ...
- 1,043
8
votes
4
answers
52k
views
Why don't we get a shock touching neutral wire?
Neutral wire has a V same as ground i.e almost 0. Also it carries some current. So if we touch the wire don't we to become a part of the circuit? Even if we are on the ground and current should flow ...
- 113
8
votes
5
answers
73k
views
What is the voltage of an average carpet static shock? Can you make it lethal?
I think I heard somewhere that it was in the thousands of volts, but it had extremely, extremely low amps. Could you somehow transform the current to make it larger or something? Or does the equation ...
- 1,968
8
votes
4
answers
2k
views
What's the point of an RMS value? [duplicate]
the RMS (root mean square) value of $f(x)$ is defined as:
$$f(x)_{rms}=\sqrt{\frac{\int^b_a (f(x))^2dx}{b-a}}$$
Why do we do this very specific thing of taking the square, the mean, and then the ...
- 267
7
votes
5
answers
3k
views
How does a resistor "know" to increase the potential difference across its ends?
My book says that current has to be constant throughout a simple series electrical circuit consisting of wires, a cell and few resistors, and hence resistors have higher potential difference across ...
- 1,250
7
votes
3
answers
22k
views
Questions about voltage
For some reason, I feel like the concept of voltage is escaping my grasp. I've done much research on these forums and through texts, and come across answers that seem quite well thought out, but still ...
- 929
5
votes
6
answers
16k
views
How power lines use high voltages with a low current?
I've read that power lines use high voltages and low currents to reduce power loss due to resistance. Looking at the formula for power -
P = VI
So to increase P, you increase V rather than I for ...
user86680
5
votes
2
answers
140
views
What is the "closed circuit" of a bug swatter racket?
There are bug swatter racket that can kill fruit flies, mosquitos, or flies, if the insect touches the metal mesh.
However, when I look at the construction of the device, the metal mesh is all one ...
- 241
5
votes
4
answers
38k
views
Among current and voltage which is responsible for brightness of a bulb?
In a circuit that is fitted with a bulb, which is the factor that affects brightness of that bulb: current in the circuit or the voltage offered by the battery in that circuit?
5
votes
2
answers
4k
views
Why can't I connection the anode of a battery to the cathode of an other battery and get a current flowing? [duplicate]
If I touch the anode of a battery or connect the anode the the cathode of an other battery, none (or rather: a very small current) flows between those two. If I instead connect the connect the anode ...
- 797
5
votes
1
answer
734
views
How are electric and magnetic fields able to travel through space and wires, and how are they more than mathematical constructs?
Once I was taught that light is physically made up of in-phase E and B fields oscillating perpendicularly, it was a little baffling because I always thought fields were just analysis tools (or even ...
5
votes
1
answer
3k
views
Can conductor be charged?
I have a copper conductor. For a while, I apply a voltage of $12kV$ DC from a source. After removing the source, will the conductor stay charged from the source if is not earthed? Will it discharge ...
- 185
4
votes
4
answers
3k
views
Are square wave really square or are they always relative approximations using harmonics
I'm studying the properties of waves through different mediums, and got hung up on this.
Is a square wave always a sum of harmonics or can we produce a square wave by quickly changing voltage? Is ...
- 153
4
votes
4
answers
3k
views
How does resistance convert voltage to current? [closed]
This is a statement that I read mainly on books about electronics.
Could someone explain why after the resistance current is what makes things work and not voltage?
Example from the Art of ...
- 2,786
4
votes
4
answers
14k
views
What does it mean when we say that power of a bulb is 10 W? Since $V/I=$ resistance is a constant, how can power $=VI$ be a constant?
My question is simple. In Ideal situation, at constant temperature, we know that normal appliances like a filament bulb has straight Voltage vs Current graph, meaning its resistance is constant or ...
- 2,366
4
votes
2
answers
8k
views
If I charge a battery using a much higher current, can it explode?
If I have a 12V 4Ah lead acid battery and use a battery charger that, let's say for example, can charge 10A, 50A, or 100A. If I theoretically turned it to 100A will the battery explode?
I understand ...
- 141
3
votes
3
answers
560
views
Since voltage determines an electron's energy, why is it current rather than voltage that is harmful? [duplicate]
Electrons have more energy with higher voltage so it seems that voltage would be what actually determines how harmful it is, because it would have more energy to lose.
- 635
3
votes
7
answers
5k
views
Why is high voltage dangerous?
High $V$ low $A$ electricity is transformed into low $V$ high $A$ through a step down transformer for safer use in homes.
But how is it any safer? The wattage is the same for the pre-transformer ...
- 1,831
3
votes
2
answers
4k
views
Electric power for current density
The electric power produced by a current $I\in\mathbb{R}^+$ and a voltage $V\in\mathbb{R}^+$ is
$$
P = IV.
$$
Now the current is given as an (alternating) current density $J(\mathbf{x},t)=\Im(e^{i\...
- 343
3
votes
4
answers
5k
views
How much current will go through my body if I were to put my finger in an outlet?
i know this is a silly question, but i couldn't manage to wrap my head around it. I am kinda new to electronics.
My home's outlets provide 220V. Upon doing some (a lot) research, the current that ...
- 41
3
votes
1
answer
5k
views
What is the difference between electric spark and electric arc?
In my student book they separate these two and indicate that sparks need high voltage to occur while arcs need low voltage with normal or low pressure and electric arcs CAN come with heat and bright ...
- 59
3
votes
1
answer
2k
views
The shape of the graph of the equation: $V= -r I + E$
I have recently collected data (for a school experiment) in order to measure the EMF and the internal resistance of a solar cell. The data complied with the equation: $V = -rI + E$, i.e. the voltage ...
- 31
3
votes
1
answer
2k
views
How does a voltage independent current source work?
I'm having some trouble understanding what a voltage-independent current source is. How can you have a current without a voltage? As I understand it, voltage or EMF is the force that drives the ...
- 153
3
votes
2
answers
6k
views
Calculating Electrical Shock 'Danger'
I managed to shock myself and wanted to see how dangerous that shock actually was to me (to figure out how much of an idiot I was). So I looked around for information on how to 'calculate' the various ...
- 47
3
votes
1
answer
230
views
Is their a visual difference between air-gap sparks of the same voltage but different current?
For example, if this spark gap has a kilovolt of power behind it @ 1A and the other is also at a kilovolt but is @2A will there be a visual difference (i.e. will the one with higher current be thicker,...
- 1,968
3
votes
1
answer
3k
views
What is fatal? Current or voltage? [duplicate]
I have been searching this answer for quite a while. I asked my physics teacher and he said it is current that causes death. A friend of mine, who is a EE student, and his answer was voltage. When i ...
- 3,003
2
votes
5
answers
94k
views
Will a bulb glow brighter if voltage is increased but current remains the same?
I understand that increasing voltage increases the energy given to each coulomb in the circuit, so in theory more energy given to a bulb should make a bulb glow brighter. But also if voltage is ...
- 260
2
votes
4
answers
7k
views
How can there be a voltage when there is no current?
I'm told at school that the Electromotive Force (e.m.f) of a battery equals the potential difference between the terminals of the battery when there is no current.
How is that possible? How can there ...
- 121
2
votes
2
answers
39k
views
Confusion about P=VI and V=IR
If we look at $P=VI$, we see that if the current doubles then the potential difference is halved
but this doesn't seem to make sense according to $V=IR$. If we look at that equation, since the ...
- 23
2
votes
2
answers
423
views
Fundamentality of voltage to current
From Ohm's Law :
Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points.
I would like to know if ...
- 990
2
votes
3
answers
1k
views
Why does current remain constant in a series circuit although the rate at which they flow deceases due to the collisions they go through? [duplicate]
I am really confused and frustrated as I can't figure this out. If someone could clear my doubt, I'd be really thankful.
According to my textbook current is the rate of flow of charge, it is ...
- 35
2
votes
1
answer
563
views
Why does increasing the voltage across and incandescent bulb increase its temperature?
I increased the potential difference across and incandescent bulb and noted the change in voltage and current, which, of course, changed proportionally. Why does increased voltage increase the ...
- 69
2
votes
1
answer
606
views
Power loss in power cable contradiction
To minimize the power loss in long-distance power cables it is best to minimize the current and maximize the voltage. This is because the power loss in the cable is calculated by $P=VI$, which we can ...
user260791
2
votes
1
answer
718
views
Kirchoff's voltage law applied with no circuit elements
Imagine a 1.5V battery with both terminals connected securely via a paperclip.
According to KVL, the sum of voltage drops in the circuit (total energy dissipated across circuit elements) must equal ...
- 161