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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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1answer
19 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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0answers
15 views

calculate the scattrering matrix of a 3-port lumped element network

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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0answers
13 views

What would be the voltage between two batteries connected in series with opposite polarity [on hold]

What would be the voltage between two batteries connected in series with opposite polarity
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0answers
15 views

Why does the computer start from sleep mode when I discharge static electricity about 1 metre away?

The situation When my colleague leaves work for the day he puts his computer in sleep mode. In the mornings I usually arrive to work before him, his computer still being in sleep mode. The floor is ...
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0answers
16 views

Resistance between any two point of an undirected graph [on hold]

Here is the circuit with 11 resistors and each named by its conductance ($G_{1}=\frac{1}{R_{1}}$). Assume the potential of each node ($U_{1}, U_{2},...U_{7}$) and say the current pass each resistor is ...
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0answers
38 views

Electrical curcuit problem, calculating current and voltage over resistor [on hold]

Can you help me calculate current over the 20 ohm resistor and voltage over the 30 ohm resistor. Answers are supposed to be 1.8A and 36V but i cant figure out how to get to that answer.
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2answers
122 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
58 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
110 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
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1answer
23 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 ...
0
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1answer
34 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
27 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
37 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?
3
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1answer
43 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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0answers
21 views

Need help in circuits [closed]

So I m not a undergrad student yet and I have some difficulties while measuring the equivalent resistance of a circuit. Specially from those complicated diagrams and so on. So I deadly need advise in ...
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4answers
76 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
34 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
25 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
20 views

Kirchoff's rule DC circuits [closed]

I understand how to solve for the unknown variables but I have trouble labeling the currents and finding the current and junction equations
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0answers
10 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
49 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
33 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
26 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
56 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
52 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
44 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
52 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
31 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
32 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
202 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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0answers
18 views

Best method for determining tolerances based on production data [migrated]

Say I am producing a wound coil which is ultimately going to be used in a colpitt's oscillator circuit. I measure the Ls and Rs of the coil, and then install it in a ferrite and then test it in the ...
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1answer
54 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 ...
2
votes
2answers
76 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
71 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
19 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
50 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
52 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
32 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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0answers
6 views

BJT as a switch: what am I doing wrong? [migrated]

I'm studying the following circuit The image is explicit but as you can see the input measured in the upper terminal is a square wave with $E_c$ and $-E_c$ as levels. Now I also had no trouble ...
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1answer
27 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
40 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 ...
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0answers
17 views

Capacitors in Amplifiers [migrated]

I am reading about single stage CE Amplifiers and I don't understand how the capacitors work here. 1) Coupling Capacitors: "The coupling capacitor is used to isolates the d.c. of one stage from the ...
3
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2answers
90 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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0answers
22 views

Find the equivalent resistance between points a and b. Please explain in detail how u solved it [duplicate]

Find the equivalent resistance between points a and b. Please explain in detail how u solved it.. Please help me.
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1answer
65 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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4answers
67 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
52 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 ...