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Questions tagged [electric-circuits]

An electronic system, with closed loop current flow, and relative electrical potentials present across electrical components.

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3answers
53 views

Brightness of lamp

Brightness of lamp (power) depends on two factors: Current which flows through the lamp. voltage (p.d) across the lamp. In the figure: When the variable resistance increases, what happens to the ...
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1answer
22 views

How Ground wire triggers breaker?

From the best of my understanding Ground wire are having less resistance than the live wire and when short circuit happens , current flow through ground wire , which allow higher electricity flow ...
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1answer
53 views

Voltage between two points in circuit

Calculate the voltage between terminals a and b. I am confused about a problem. I've tried to solve this using the second Kirchoff's rule, but my solution is equal to 0. What am doing wrong? E=5V R1=...
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2answers
15 views

Can we define rms current for pure inductive and capacitive ac circuit?

For a purely inductive and capacitive ac(sinusoidally varying) circuit, average power dissipated across a capacitor or an inductor is zero. Then does that mean RMS current is zero?
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2answers
31 views

What happens to a system of capacitors when a dielectric is inserted into one of them?

sorry for my English. While doing some homework I've stumbled upon this "circuit": the system is connected to the same potential difference through a generator that is connected to points A and B. ...
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0answers
48 views

Resistance between any two point with unknown current direction

A resistor-network which can be expressed as a weighted, undirected graph (like the following figures). The Y-Δ transform shows: the effective resistance between any two points could be written as a ...
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1answer
33 views

When two wires touch, electrons can flow from one to the other. Is that a metallic bond?

If two very hot wires touch, they melt together to form one wire and electrons can flow between them. If two cold wires touch, they do not melt together to form one wire but electrons can still flow ...
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2answers
178 views

Voltage Drop Explanation. Is it correct?

When the battery is turned on, a wave propagates within the circuit to determine the current of the sytem.At this point, the current is inhomogeneous withing the circuit(but this dissapears almost at ...
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1answer
28 views

RC circuits - what can we interpret when the voltage across the capacitor is equal to zero?

When applying the law of addition of voltage in RC series circuit with alternating sinusoidal current, we notice that voltage across the generator is equal to the sum of the voltages across all other ...
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2answers
82 views

Common potential of two capacitors

I read in my textbook that when two isolated capacitors are connected to each other, redistribution of charge takes place in such a way that they both acquire a common potential. My question is why ...
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0answers
54 views

Calculate the scattering matrix of a 3-port lumped element network [closed]

I can get S11 and S12 by terminating port 2 and 3 with Z0 and Zr respectively. But when I try to calculate S13 it seems less straight forward. The following is the network, taken from Gao, J. The ...
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2answers
141 views

How far do electrons actually move along a conductor under an alternating current?

This is more or less a curiosity question. But I have had really good luck with stack exchange so far. If I can expand on my question a little bit - it may not be super important, but I know under say ...
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2answers
69 views

Current without EMF in AC capacitance circuit

In AC circuit with only capacitance, current in circuit is maximum at time t=0 but emf of source is E=0 at t=0 , how can this happen, How can current flows without emf.
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4answers
115 views

Basics of electric current

I am a mathematician who never took a physics class besides classical mechanics. Recently I have been looking at biophysics for a small project and I have a hard time understanding the basics of ...
3
votes
1answer
30 views

How are free electrons produced in a gas?

I'm aware about ionisation but even to ionise a gas you need an electron. So how in a discharge tube, which has a low pressure gas and a high voltage, does current flow? How is the first electron ...
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1answer
48 views

Brightness of lamps

The brightness of the lamp (power) depends on two factors: The voltage and the current which flow through it. In Figure(A) as the variable reaistance increases its reaistance, the current which flow ...
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1answer
34 views

Potential divider

I am just wondering if a potential divider circuit is used to vary the pd across the other resistor from zero to maximum, why can't the variation be done straight from the source?
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1answer
45 views

Self-induction and conservation of energy [closed]

back EMF when switch is open is greater than back EMF when it is on; is that opposes the law of conservation of energy?
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1answer
51 views

Does the cold affect electrical conduction?

Disclaimer: I'm not experienced in many phyiscal nor electrical terms and I have no idea where to ask this question elsewhere. I'd be open for a move request if needed. Today when using public ...
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4answers
87 views

How does an ideal transformer satisfy law of conservation?

I have read in books and articles that, keeping the power as is transformers increase the voltage and therefore reduce the current as per the formula $$ P = IV $$ and this results to reduction in ...
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1answer
36 views

What is difference between current and voltage? [closed]

If current passes through the bulb not using it up then how battery becomes weak after sometime?
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1answer
31 views

AC circuit with resistor

As you can see from the image that "potential drop must be equal to the applied emf". This means after that point there is no flow of current as potential difference is zero.But how is this possible?...
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0answers
17 views

Finding resistance and how many appliances can be connected

A household electricity system can be modelled as a fuse in series with appliances, all of which are in parallel across the 240V mains supply. In one household there is a 16A fuse in series with the ...
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6answers
77 views

Why doesn’t current decrease when it passes through a resistor?

As far as I know current is the amount of charge passing per unit time. $$I=q/t$$ When current passes through a resistor, the resistor resists the flow of current so the amount of charge going to ...
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2answers
43 views

Hot Wire vs neutral wire [duplicate]

How can a wire be called the "hot" wire and another the "neutral" wire when ac current reverses itself 60x/sec? For first half of a given cycle it flows from the "hot" wire to the load and back out to ...
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1answer
27 views

Why is the open circuit voltage equal to Thevenin's Equivalent Voltage?

When we are taught Thevenin's Theorem, we are taught that the equivalent voltage Vth is the voltage obtained at terminals A-B of the network with terminals A-B open circuited. But why is it true?
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2answers
62 views

Charging and discharging a capacitor [closed]

So from what I understand, in the case for the charging capacitor, I understand the voltage across the capacitor as well as the charge can be given as the function of time: $$V(t)=\epsilon(1-e^{-t/RC}...
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2answers
57 views

RC circuit confusion [closed]

I was doing some RC problems in A levels, and in ine of thr problems it was about a circuit attached as a picture: My question is can someone clearly explain to me why when time goes to infinity , ...
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3answers
52 views

Is natural frequency of an LC circuit equal to angular frequency ? Why don't the units match?

When I was reading the L-C circuit in my textbook I came across the derivation of equations of instantaneous charge and current. Which is no problem, but when I got to the derivation to current . ...
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2answers
84 views

How is a capacitor implemented in Kirchoff's Loop Rule?

I'm real stumped here. I may be missing something, but I'm genuinely perplexed as to how one would add a capacitor to the list of elements being added to an equation through Kirchoff's Loop Rule (KVL)...
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1answer
32 views

How to measure an electron plasma with an electrically biased probe?

I want a crude way to confirm the existence of an electron cloud in a moderate vacuum of 2 mTorr. In my set up, filaments emit electrons into a magnetic trap which concentrates them (similar to an ...
2
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0answers
36 views

Why are(n’t) rechargeable batteries damaged by partial charging?

Originally asked in ElectricalEngineering.SE, but I was told Physics.SE might be a better place to ask. Over the years, I've come across websites and people with different opinions on the "correct" ...
3
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5answers
226 views

Why isn't there a minus sign in Ohm's law, $V = IR$?

Suppose current runs through a resistor from left to right, and we define the left-to-right direction as positive. Then from left to right, the potential decreases. So $V,$ the voltage across the ...
9
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4answers
1k views

How do I deal with “crossing resistances”? [closed]

I'm doing some physics homework calculating the total resistance between points A and B and while some circuits are comprehensible, there are two that I can't understand how they work at all. So, it ...
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1answer
59 views

Shouldn't there be short circuit everywhere?

Live wire and neutral wire should never come in contact otherwise there will be a short circuit... but when we take a two pin plug and insert it into the socket then at that time we don't see whether ...
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2answers
93 views

What is the equivalent resistance between $A$ and $B$ in the given circuit? [closed]

Hi, I've been doing some current electricity problems by using Kirchhoff's laws. I've tried applying KVL(Kirchhoff Voltage law) to this circuit, but to no avail. There happens to be too many variables ...
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1answer
73 views

How to differentiate Capacitance (Italized C) and Coloumbs (regular C) on paper [closed]

I am doing a question on capacitance and coulombs. I got the answer correct, but I was wondering how a physicist, when doing the calculation on paper, would differentiate a C and C?
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2answers
42 views

Principle of potentiometer

I could not understand why the emf of the main cell (labelled E) in the circuit (can be a battery eliminator) should be greater than the emf of the cells (E1 and E2) used in the secondary circuit. ...
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4answers
66 views

AC/DC vs conventional/electron flow current

Conventional current is from positive to negative and electron flow is from negative to positive. If we go with conventional current sign, would it be right to say DC current is always as per the ...
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1answer
42 views

Is there any way to determine how long a wire is?

This is for transmission lines applications. Are there any way to know how long the wire like by getting the resistance of the wire(but how). Or is it possiblee to charge the wire until it produces ...
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3answers
60 views

Ohm's Law and transmission of electricity

Electricity is transmitted at high voltages. It is said that this reduces current and consequently resistance. But according to ohms law, low current must face high resistance. How is this ...
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1answer
36 views

At what pressure do semiconductors break down? [closed]

So let's say you were going to send some electronics to the bottom of the ocean, 3-5km down. This would be about $5km*1000kg=5Mkgf/m^{2}$. So at what pressure do circuit boards, transistors, etc stop ...
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1answer
28 views

What skills are required to deal with almost every DC problem? [closed]

What skills do you recommend me to learn so that i can deal with almost every DC circuit problem and simplify any combination of resistors regardless how complex is it? Surely there's nothing magical ...
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1answer
45 views

Misconception about flow of charges

Let's say I have a 5V battery connected in the manner shown in the diagram. I've tried this setup with all sorts of things like pouring brine(salt water) into the soil to decrease its resistance so ...
3
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2answers
97 views

Does current flow when you connect a battery to earth?

Let's say that the earth has 0V and everything is ideal, does current still flow and why?
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1answer
68 views

Are these two circuit equivalent? [closed]

are the two circuits equvalent ? I have actually got a different problem (wheatstone bridge) but,I want to make sure that there is no mistake in my assumption before asking that question. In the ...
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5answers
94 views

Potential Difference of a battery - What does it mean?

I have studied current electricity for a while now. When I look back at basic concepts, I am quite clear about what current, electron, resistance is. But I cannot imagine about the potential ...
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2answers
60 views

Potential difference of resistors in parallel linked systems

Before the question I want to explain somethings to see if I understand anything wrong please tell me if im wrong: When there is a Potential difference on a system then the electrical charge will move ...
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0answers
21 views

Electricfield and faraday's law [duplicate]

Consider RL circuit consisting of a battery , resistance , inductor , and switch .all components are in series . If we close the switch at time t =0 the current will build up until reaching a maximum ...
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3answers
81 views

Electrons and wires [duplicate]

The electrons that carry the electric energy are in wires or in the battery ? battery provides a potential difference but from where electrons flow to make for example a bulb light. If they flow from ...