# Questions tagged [electrical-resistance]

The tag applies to electrical resistance and resistors. DO NOT USE THIS TAG for non-electrical resistance.

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92 views

### How does current get reduced in resistor?

How does the resistor reduce the current? I know that when there is no resistor in the circuit the current is higher than the current when there is a resistor. But, my question is: How the resistor ...
47 views

### How long does a headphone last on a given battery? [closed]

Sennheiser HD 598 has 50Ω impedance. It has a 3.6mm cable, but I am planning to do a simple DIY project to replace the cable with a bluetooth receiver, a 3.7V 1000mAh battery (and a charging board). ...
28 views

### Current in an resistor [duplicate]

Suppose I have a electric circuit as shown in image Let a resistor is connected to a battery. The current starts flowing through the resistor. Why is the current entering the resistor the same as the ...
42 views

### High voltage in electric power transmission systems - why Ohm law is used regardless of "assuming the power is completely converted into heat"?

Similar questions feature found about 10 QA's here on the subject with all about 1-5 cumulative upvotes. For example Why do power lines use high voltage? have 6 upvotes for accepted answer: The line ...
22 views

### What will be the currents through $R$, $L$ and $C$ at $t=0$ + (The complete question's provided in the image attached below)? [closed]

Choose the suitable alternative(s) Elements R, L, C are connected in parallel and excited by a DC source of l Amp. If IR. iL and ic are the currents through R, L, and C respectively. then at t=O+ i) ...
39 views

### How can current be constant and still result in resistors having a voltage drop?

My issue arises when thinking about the situation like this. Current is the amount of charge flowing through an area, and resistance is basically they difficulty in doing so. My issue results when ...
51 views

### Can I apply Kirchhoff's current law to two separate nodes which are connected only by an ideal wire? [closed]

Suppose there are 2 nodes A and B in the above circuit. If A has 2 incoming currents $I_1$, $I_2$, and B has 1 incoming currents $I_3$, $I_4$, is it correct to write the equation of whole nodes and ...
35 views

### Maxwell’s first equation in conductor we take E=0. And I have read that’s true for practical time scales. But in 4th equation we use non zero E, why?

\begin{align} \nabla\cdot E&=0\\ \nabla\cdot B&=0\\ \nabla\times E&=-\frac{\partial B}{\partial t}\\ \nabla \times B&=\mu J+\varepsilon\mu\frac{\partial E}{\partial t}=\mu\sigma E+\mu\...
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### What potential difference or current would kill a person?

I was watching this YouTube lecture, and earlier in the vid he mentions 120 volts from a power outlet would kill you. So if human resistance is $300\ \Omega$, $0.4 \rm A$ should be enough to do the ...
37 views

### Is electrical resistance analogous to friction?

In a circuit, an electric field is produced from a circuit element providing a voltage source. Electrons flow through the circuit undergoing collisions which provide a resistive force to the electrons ...
53 views

### Circuit problem [closed]

Hello, can someone please help me on this problem? Question: calculate the potentials at A and B. The solution says that they are both 12V "due to symmetry" but I have no idea what is the ...
358 views

### What good reason to hang long cable carrying electric current high above the ground? [closed]

Assume no flooding or other natural disasters to damage the cable if it is laid beneath the ground, then what good reason for them to be suspended high above the ground? The cables are insulated and ...
21 views

### Temperature coefficient

If we raise the temperature of any conductor the atom, free electrons starts vibrating There kinetic energy increases If kinetic energy increase then , Current must be increase As current increase ...
43 views

### Does the resistance of a filament lamp change?

Recently in a work book there has been a question to explain with the aid of a circuit diagram the method a student could use to investigate how the resistance of a single lamp changes with potential ...
29 views

### I don't understand why for resistors in AC circuits the phase angle between voltage and current is zero

From the following graph I understand it is because they reach the voltage and the current reach their maximum values at the same time on the resistor, but I don't understand why this should be that ...
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### Huge current flows when there is no resistance, consequently, the potential difference is 0 but no current flows if no cell is added to the circuit

If $R= 0$ , $V= 0$ and $I=$ $max$ (i.e. charges are flowing at a huge rate), but when there is no potential difference applied to a circuit, charges don't flow. That means huge current flows when ...
4k 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) ...
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### What would happen if we were to put a resistor at a junction?

I am currently studying electrical circuits in high school, and at some point I wondered what would happen if we were to create three (or more) connections on a component and put it at a junction. For ...
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### Voltmeters / direct measurement of voltage in a circuit

I was wondering that many instruments that measure the ddp in a circuit works measuring instead current and then applying Ohm's law. When I looked for how Ohm made his initial measurements for voltage,...
32 views

### Is effective EMF always greater or less than individual EMFs?

When we connect many Resistors with Resistance = $R_{i}$ in series, we get an equivalent resistor with resistance equal to $R_{eq}=R_{1}+R_{2}+R_{3}...$ This logically implies that the equivalent ...
23 views

### What are the steps that give rise to this following resistance equation for a diffusive transport of electrons?

$R = R_b (1 + \frac{\lambda}{L})$ Source - page 6 of this book: https://nanohub.org/courses/FON1/01a/asset/15698
46 views

### Why my electromagnetic coil generates a weak field and increase its resistance when I use higher voltages? [closed]

I've been trying to build a coilgun, so I winded a cable around a 7cm long pvc tube (the diameter is 2 cm). The cable is composed of about 30-35 parallel wires so I calculated the general resistance ...
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### Is the terminal voltage twice the EMF when the battery is being charged and short circuited?

So, I know V terminal= E- Ir during discharging of a battery. 'E' is the EMF, 'r' is internal resistance of the battery and 'I' is current. If the battery is short circuited, 'I' becomes = E/r because ...
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### Why can't both the formulas $I^2R$ and $V^2/R$ be used to find energy lost in a supply cable?

![ have two points both of which I find correct. But I also find that both can't be correct at the same time. Because they contradict each other. The V in VI and the V in V²/R 'are the same thing' (...
60 views

### Is there anything other than Resistance, Capacitance, Inductance in a circuit? [closed]

Resistance, Capacitance and Inductance measure certain electrical property of some matter. These term have even given rise to objects like resistors, capacitors and inductors respectively. Few ...
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### How does the conductivities of metals and semiconductors vary when placed in the presence of magnetic field?

Suppose you have two materials one is a metal and other is a heavily doped semiconductor and they are placed in a magnetic field. What experiment will you do to distinguish between them? Does the ...
43 views

### What is the significance of Power factor?

I was studying the power in Alternating current. The formula to calculate the power in alternating circuit is $$P = VI \cos{\Phi}$$ where, $V$ and $I$ are RMS values of voltage and current and $\Phi$ ...
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### Modelling electrical conductivity in low-dimensional nanostructures

I know that the Boltzmann transport equation can be solved under the Relaxation Time Approximation (RTA) to obtain the electrical properties of materials. However, the parameter that I am interested ...
35 views

### EM waves with complex conductivity

In the solution of Maxwell equations inside conductors, $J=\sigma E$ is used. In the derivation of e.g phase difference, and skin depth, $\sigma$ is assumed to be real, e.g $e^{-b\cdot r}$ is the ...
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### Ohm’s law holding true on temperature-dependent resistances

As far as I know, Ohm's law (in macroscopic form) states that the in some devices/conductors/materials, the (instantaneous) current through the device is directly proportional to the (instantaneous) ...
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### Why does the potential of both power supplies drop when only one is needed to maintain the current?

In the circuit shown above, the current through the ammeter is the sum of the currents through each power supply. By Kirchoff‘s Voltage Law however, we can treat each power supply to be in an ...
2k views

### Why does a drop in resistance lead to a drop in voltage?

I was working on this question which I know the answer to but I am still confused. I get that resistance is due to collisions on the atomic scale where the electrons' kinetic energy is transferred to ...
47 views

### The relationship between impedance, resistance and resistivity and which are purely material properties

The resistivity of a wire, $\rho$, is purely a material property. For a wire of length, $l$, and cross-sectional area, $A$, the resistance, $R$, is given by $$R=\frac{\rho l}{A}$$ which depends on ...
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### British Physics Olympiad Round 1 2010 Q2a - Find potential difference between A and B [closed]

I've been trying some British Physics Olympiad past papers. In the 2010 Section 2 paper, the first question is the following: I've never seen a circuit like this, and I'm unsure what the correct ...
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### A circuit with 2 resistors in series - current in between them

Let us have this circuit: We know from Kirchhoff's laws that the current I1 entering R1 and current I3 exiting R3 are the same, I1=I3. But the point that bothers me is that: we know according to Ohm'...
101 views

### Resistor Cube Problem Intuition

In the well-known resistor cube problem using a resistor cube with equivalent resistors on all the edges, the prescribed approach to solving it involves merging points of equivalent potential as shown ...
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### Resistance of a resistor - dividing infinitisimals [closed]

Given a resistor with the shape of half a sphere with inner radius of $R$ and outer radius of $3R$. The sphere has a conductivity of $\sigma(r)=\frac{\sigma_0 R}{r}$. A current is inserted in the ...