All Questions
173 questions
0
votes
1
answer
85
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What is resistance precisely?
Is there a mathematical definition for resistance because I cannot find any. On the internet I find definitions such as:
The electrical resistance of an object is a measure of its opposition to the ...
- 55
-1
votes
0
answers
16
views
Speed of current at higher and lower potential [closed]
It is said that, charge has more potential energy at higher potential as compared to lower potential in an electric circuit. So, is the speed of current faster at higher potential and slower at lower ...
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
0
votes
1
answer
38
views
Ideal Superconductor connected to Zero Voltage
If an ideal superconductor was just left alone, with no potential difference, what would be the current flowing in it?
According to Ohm's Law, $V = IR$
Hence, if a superconductor of $0\Omega$ ...
0
votes
2
answers
61
views
Piece of iron instead of a proper fuse
In a video game Dying Light 2, there are those electrical boxes that you open and then "fix" by putting a piece of iron (I suppose). Assuming voltage $U$ is being produced and is supplied ...
- 307
0
votes
2
answers
227
views
Explanation of Potential Difference
My question is to verify if my thought process below is correct.
So in a circuit the charge will flow (the current). When the charge flows there is resistance which is the collisions of the charge ...
- 37
0
votes
3
answers
121
views
Why won't the bulb light? [closed]
Here's what the marking scheme says: "Capacitor gets charged first and acts as an insulator/blocks current".
However, electrons flow from negative to positive, so shouldn't the electrons ...
- 93
0
votes
3
answers
126
views
Potential drop against internal resistance of cells in combination
Suppose two cells of emf and internal resistance e1, r1 and e2, r2 respectively are connected in series. The negative electrode of 1st cell is connected to negative electrode of the second cell. Why ...
- 1
1
vote
3
answers
1k
views
Does current make the full return trip?
In an AC system, the neutral wire is said to provide a return path for the current back to it's source. Given that the current is said to be alternating back and forth, how does this work, does the ...
- 13
0
votes
1
answer
39
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When using a screwdriver tester i am completing the circuit with 110v?
if i use a screwdriver tester, i am part of the circuit with 110v passing my body? isn't this dangerous?
- 3
0
votes
1
answer
80
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"Why do power lines use high voltage?" Loss in power equal to Current*Voltage? [duplicate]
I define P is the average power. So $P=IV$ and $I=\frac{P}{V}$.
$P_{loss}$ I define to be the power loss, which is equal to $I^2R$.
Substituting for $I$, $P_{loss} = \frac {P^2R}{V^2}$
So I get that ...
- 93
1
vote
1
answer
56
views
Potential divider problem [closed]
What does the curved arrow represent? The answer states that L1 will be dimmer than L2.
From my current knowledge, moving the contact K closer to X will somehow increase the voltage of L2 meaning it ...
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
0
votes
2
answers
357
views
Voltmeter connected to parallel circuit
This is my current understanding. Voltage is defined to be the potential difference between 2 points, hence it only makes sense for a voltmeter to be connected in parallel. But why must this voltmeter ...
1
vote
1
answer
124
views
Transformers in Power transmission [duplicate]
Recently I learnt that transformers are used in the national grid to increase the voltage, so we get less current. But my understanding V=IR and by increasing the voltage we get more current, so what ...
- 69
0
votes
3
answers
1k
views
How does current actually flow in a wire?
When I was in my school I was taught that the electric field due to the battery is along the wire (from $A \rightarrow B \rightarrow C \rightarrow D $) and these are responsible for electrons at each ...
- 8,476
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 ...
1
vote
1
answer
229
views
High voltage in transmission line [closed]
I'm trying to understand why high voltage is used in transmission but I seem really confused by the explanations I read.
Here's what I could make out:
$$P_\text{loss} = \dfrac{ΔV^2}{R_t} = \dfrac{(...
- 349
0
votes
1
answer
97
views
Does an open circuit have electrons accumulate in it?
This is what I have imagined electricity to be like, where the blue balls represent the free valence electrons in a conductor atom, and the electrons flow towards the positive electrode as the ...
- 1,250
1
vote
3
answers
125
views
$I$ proportional to $V$ or vice versa?
I am confused whether Voltage depends on current or the vice versa. I always thought that the vice versa was correct. I tried to find the answers of some of my other conceptual doubts on the web but I ...
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
1
vote
1
answer
2k
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Why increasing the resistance in a series circuit decreases the current in the circuit?
Concise Physics mentions that:
On connecting one more appliance in the same circuit , the resistance
of the circuit will increase . Hence , it will reduce the current in
the circuit , so each ...
-1
votes
2
answers
223
views
How does the high potential difference between the two points ionizes the air?
As we can see that for some instance air can tolerate the potential difference between two points without any high leakage current and when this potential difference between the two points becomes too ...
- 972
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
0
votes
1
answer
47
views
Confusion regarding drift velocity and potential
From this post I understood that the drift velocity of electrons decreases further into the circuit. But my book says that electrons move with constant velocity throughout the circuit, and both of ...
- 1,250
1
vote
2
answers
293
views
Does a higher voltage always mean a higher electric field strength?
In a step-up transformer, the output voltage is higher than the input voltage, while the output current is lower than the input current. Basically, since P = VI is conserved, the current has to ...
- 337
0
votes
1
answer
200
views
EMF of source depends on the charge and the path then what do we mean when we say EMF of a source is $\epsilon$?
EMF of an EMF source (a battery for example) is defined as the work done by the non-conservative force(s) on charged particles as it passes through the terminals of the source divided by the charge of ...
- 510
0
votes
2
answers
702
views
Electric potential and kinetic energy in any flowing charge
We just started with electricity in school(grade 10) and I have some confusions regarding electric potential.
According to my book,
The potential at a point is defined as the amount of work done per ...
- 1,250
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
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
1
vote
4
answers
1k
views
Current vs voltage in high voltage transmission lines
I know this question has been answered many times, but sadly I'm still not quite sure I get it.
Here's my interpretation, please correct me at any point:
We have some source. There's various ways to ...
- 135
1
vote
2
answers
40
views
Resistance And Electric Power
In a practice problem A motor rated at 20 A with a voltage of 115V exerts a force of 4900 N over a distance of 10 m in 30 s. Using the formulas $P=VI$ and $P=\frac{Fs}{t}$, we can see that the motor ...
- 307
0
votes
1
answer
460
views
Why is the brightness of a light bulb dependant on power?
If:
Temperature is a measure of the average (kinetic) energy of the particles which make up some material
Power is measure of energy transferred per second (J/s)
The temperature of the filament in a ...
- 33
2
votes
2
answers
3k
views
Why is high voltage more deadly than low voltage?
Why is higher voltage said to be more dangerous? Doesn't higher voltage decrease current as P = IV where P is constant, thus making it less deadly?
- 323
1
vote
2
answers
154
views
On a nanoscopic level, what really happens to the electrons in the secondary coil of a step-up transformer?
I know that when AC is passed through the primary coil of a step-up transformer a higher emf is induced in the secondary coil (with more turns) of the transformer. Since energy is conserved, and P = ...
- 337
2
votes
2
answers
184
views
Confusion over Van de Graaff vs. Electric Fence
It is said "It is not the volts that kill you, but rather the current".
However, volts is directly related to current as V= IR (current x resistance).
Since the resistance of one particular ...
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0
votes
0
answers
53
views
Does a bulb offer still offer resistance even after it gets fused? [duplicate]
Sorry, for my naivety this is my first time posting here.
But, my question is that will the bulb offer any resistance after it's fused?
I know that no current can flow though the fused bulb i.e. $I=0$....
- 101
2
votes
1
answer
600
views
Will I get shocked if I touch only the live wire while standing bare feet on the dry floor of my appartment?
In contrary to static electricity the mains electricity must return to the power plant. When I touch the live then the current flows through my body and the floor of my appartment and through soil to ...
- 170
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
-1
votes
1
answer
199
views
Electric arc and electric spark differences? [duplicate]
Why does an electric spark occur discontinuously while an electric arc is not extinguished as long as the current is maintained?
- 59
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
0
votes
2
answers
324
views
Why current drops when voltage increases?
https://www.youtube.com/watch?v=ubZuSZYVBng&t=329s
In the video above the man put a 200 thousands volt ball near a non-charged one and a very tiny current appear between them. But I think with ...
- 59
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
0
votes
2
answers
838
views
How does current flow through the earth and back to the supply to break the fuse?
From my textbook, it says when the live wire touches the metal casing, a current will flow to the earth and blow the fuse located in the live wire. But through what devices will the current flow after ...
- 113
0
votes
1
answer
273
views
Power and power loss during transmission of power
So let's say power to be delivered to homes is 80 kW($P_3$ = 80 kW) and the houses have to receive it at 220 V ($V_3$ = 220 V). The substation is a 4000 V to 220 V step-down transformer and $R_2=15\ \...
- 15
0
votes
1
answer
766
views
What does the labelling of a conductor such as: 24 W 12 V mean? Does this mean the resistance of the wire or the current?
So I came across a question where a lamp was labelled 24 W and 12 V. 2 lamps that were identical and had this labelling were then put in series with a voltage supply of 12 V.
Obviously the individual ...
- 220
2
votes
2
answers
671
views
Ohm's law and Joules heating
Ohm's law state that the ratio of V and I gives us a constant value of R provided that the temperature is kept constant throughout. However, in accordance with the joule's heating it would get heated ...
- 29
0
votes
1
answer
229
views
Why the potential at positive terminal is considered to be high?
even though it's the electrons that move from negative terminal of the battery and gets move along the external circuit and finally enters the positive terminal of the battery and due to battery force ...
- 29
0
votes
1
answer
81
views
How do charges away from the terminal react when the switch is flipped on?
Let us say we have a simple purely resistive DC circuit. When we flip the switch a current starts flowing which after some time becomes constant. Now, I know that the electric field across difference ...
- 405
1
vote
2
answers
368
views
When to use Ohm's law as opposed to using power formula?
I am a mechanic trying to gain a better understanding of electrical theory on vehicles. I have a sound understanding of Ohm's law and also the power formula (Power = Voltage x Current)
However, I am ...
- 15