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its very simple, follow these steps 1)as the circuit tends to infinity, consider the equivalent resistance to be R(e) 2)consider the parallel resistors i.e., BC and the rest to the right of BC. these are in series with AB 3)now the total resistance to the right of BC will be equal to the effective resistance of the total circuit R(e), as the circuit tends ...


1

Hint in a parallel circuit, the voltage across each resistor is the same. What is the voltage across the $4 \Omega$ resistor?


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It is not a silly question . Potential means energy per unit charge at a point in a field . When a unit charge travels through an e-field, energy is either lost or gained as potential energy . Potential difference is the difference in P.E. between any two points in the field . In a circuit , when a cell is inserted , electric field forms and it is due to ...


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The answer depends a lot on how much into detail you want to go. Superconductivity is a pretty involved phenomenon so I hope I can help you already, by explaining why a resistor causes a potential drop. A current can be imagined as electrons moving through a conductor. During that movement, they are accelerated due to the electric field. At the same time, ...


1

In resistors, resistance, current, and voltage (or the voltage drop) are related by Ohm's law: $$ U = RI $$ This law may also be formulated in a more insightful, microscopic form, especially in the simplest microscopic version of Ohm's law (due to Gustav Kirchhoff): $$ \vec J = \sigma \vec E $$ Here, $\vec J$ is the current density, $\sigma$ is the ...


2

Electric potential is a potential energy just like gravitational potential energy or indeed any other form of potential energy. Specifically, moving one coulomb of charge through an electrical potential of one volt produces (or requires) 1 joule of energy. From your question I guess you're basically happy with this, so the question is really how this energy ...


1

I can answer that yes, momentum is definitely transferred to the surrounding lattice, though not through a direct scatting of electrons with protons. This is important in increasingly small electronics. When the cross-section of the wire or metal is extremely small, the collisions can be enough to displace the metal, and wreck a circuit. Tungsten is ...


1

The Drude model is fine for thinking about some things. (It is still taught.) The electrons collide with the atoms. (or a bit more precisely, the outer electrons of the atoms.) Since this is a classical picture perhaps it's OK to have a classical picture of the atoms. Imagine they are little sphere's all joined to the other atoms by little springs. ...


1

Wait a minute. Surrounding the protons are a matrix of electrons. These are the electrons not "cool enough" to exist in the conduction band. I imagine these are what collide with the electrons in the Drude model approach. The closer you get to those electrons, the more they're going to push back by the Coulomb potential. Furthermore, I imagine some Pauli ...


0

In drude model, Electron don't collide with protons. The best way to figure this is that the electron collides with phonons and with impurities. But the correct Drude model do not involve collision with the nucleus. The collision gives excite phonons, and can be considered as heat from a macroscopic view point. The Drude model give the right formula only ...


1

For a constant potential difference applied across two ends, $\Delta V=\int\vec{E}.d\vec{l}$ or for simple cases, $V=E.l$ When you increases the length of the wire, electric field $\vec {E}$, decreases, thus driving the charges less and decreasing the current.


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Here's one way to look at it: The electrons don't experience a potential difference: the experience a field (potential difference per unit length). Double the length = half the field. Another way of thinking about this: if the total potential difference was 9 V for a 2 m length of wire, then we know that the potential at the mid point was 4.5 V. Thus, the ...


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When you place a battery across any wire, the electrons on it starts to move. When electrons start to move, they get scattered from the nuclei present in the material which is the wire made from. This process creates the resistance. Thus, when the length of the wire increases, the amount of particles scatter from the nuclei increases which also increases the ...


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When we derive Ohm's Law using the Drude Model, we assume at one point of time that E=V/L, when is fact, E=dV/dL, unless E is constant, in which case the assumption E=V/L is true. But I don't understand why the electric field in a conductor must be constant as current flows. Generally, the electric field in a conductor does not have to be constant (in ...


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An easy way to prove Ohm's law for electric fields that aren't constant is to first assume that the electric field is approximately constant over short lengths, just like $E=dV/dL$ suggests. Using that, you can derive Ohm's law for short lengths of material, $dV=IdR$. We'll assume that "current in = current out", which is true at steady-state. This allows us ...


0

The current $I$ has a value in one point of the circuit, in contrast to the voltage $U$ which is always measured between 2 points. The definition of $I$ is the amount of charge $\Delta q$ that passes through a particular point in the circuit in the time $\Delta t$ (it's a quantity mathematically similar to the simple velocity in kinematics). So when you ...


2

I would like to point out that, except in the movies, it isn't the case that "When a short circuit occurs it's obvious that there is fire". Now it is true that, for most, "short circuit" evokes a picture of sparks and fire but, in fact, most short circuits simply result in a malfunctioning device, not sparks and fire. A practical notion of "short circuit", ...


1

In addition to already mentioned Joule heating, some types of short circuits are unstable, especially when they are under high voltage: the conductors may touch each other, make a spark, which would then give them a circuit-breaking air pressure wave impulse, then they again touch, generating another spark, and so on. Also, the spark can develop into an ...


0

On a mechanistic level it's about collisions (of electrons with with the bulk material) transferring energy from an electrical current into heat of the body of the device. In more abstract terms, in almost all processes energy ends up in the form of heat because it has the lowest entropy of any of the other available forms of energy, it is the least ...


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When a short circuit happens, provided the source impedance is null, the impedance is only determined by wires and is extremely low (let say resistance $R < 1\Omega$). Therefore, by Ohm's law, if there is no current limitation, the current drawn is high (for example, with $V_\mathrm{rms} = 230\mathrm{V}$, $I_\mathrm{rms} > 230\mathrm{A}$). In this ...


1

Using your playground example.... Imagine if you had to pass a message (electricity) across the playground, when cold you would have to stretch between each fixed person to pass this message. When hot, more people fill the gaps, the message is easier to pass. Hope this helps :)


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The other answers here are very good, but are a bit too in-depth for what I believe you're looking for. The simplest way of thinking about resistance is that the current carrying electrons are colliding with the atoms that make up the conductor. By collide I mean the electrons can interact with the atoms via the Coulomb force. The kinetic energy of the ...


1

In the classical model of Drude, the resistance come from the choc of the electron with the impurities or with the phonons (waves in the solid), depending on your materiel. The phenomenon of heating up is that you dissipate the energie given par the current by collision with phonon/impurities etc... If you want a quantum description, you should look ...


2

As for the question what "really causes resistance": When looking at a solid which has a periodic crystal structure the electrical resistance would hypothetically be zero if the crystal structure would indeed be perfect and the atoms would keep perfectly still at all temperatures. Note that resistance is a measure of how much - well, resistance - there is ...



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