# Tag Info

58

None of the processes you describe are instantaneous. Acceleration is produced without any delay on applying force. Angular acceleration is produced without any delay on applying torque. If you are looking at the microscopic scale, it takes time for fields to change in order for forces to be produces. For example, E&M changes propagate at the speed ...

18

I mean the basic principle is, you're right, this setup is described by the math of classical electrical circuits as one which should drive an infinite current, and if you only have one charge to move then an infinite current necessitates it moving with infinite speed. If you do not give it a way to lose energy then it will continue to gain energy ...

8

Supposing an ideal wire ,How do electrons accelerate and gain kinetic energy ? An ideal wire is an abstraction that is used to simplify calculations in physics and electrical engineering. The mobile charge in an ideal wire respond instantaneously to external fields so that the skin depth is zero. Clearly, this can't be the case for electrons, and so the ...

7

Kirchhoff's circuit laws (both the current law and the voltage law) apply in the lumped circuit approximation only. That means they apply when the circuit can be accurately modeled as a collection of lumped components whose physical extent is insignificant; connected by ideal wires, with no significant magnetic fields coupled to the wires, and no ...

7

This depends on our own role as observers. Our own feeling of time is of such a nature that these things look instantaneous for us. When we close a circuit it takes at least some nanoseconds for the bulb even to be able to "know" about this and some microseconds to heat up and some nanoseconds for this to reach our eye. However, human time resolution is at ...

6

If the circuit had zero resistance, wouldn't it just gain more and more energy as it loops around the circuit again and again, Assuming that the fundamental circuit-theory assumptions* hold, then if the circuit had zero resistance it would still have non-zero inductance. So the energy from the battery would go into the magnetic field of the inductance. ...

6

If you connected an ideal wire (zero resistance) across an ideal battery (no internal resistance) from Ohm's law the resulting current in the circuit would be $$I=\frac{emf}{R}$$ Which means for zero wire resistance we would have an infinite amount of current flowing. The thing is, there will always be resistance in an electrical circuit opposing the flow ...

5

The crux of your question seems to be this: One thing very very important that in this equation V refers to the potential of the resistor. Not the potential difference of the two sides. This seems to indicate some kind of confusion or misconception. There are not two different quantities of interest here, only one. People may sometimes loosely speak of "...

4

The answer is more about chemistry than physics - but then there are those who will claim that chemistry is just applied physics. There's also a bit of electronics in the mix - which is also a form of applied physics. What is the memory effect Typically "memory effect" refers to the phenomenon that a battery that is not fully discharged for multiple charge ...

3

In a charging RC circuit where the capacitor is initially uncharged, the charges will move as if the capacitor is essentially absent. Therefore, the initial value of the current is just equal to $V/R$. If the RC circuit starts with a fully charged capacitor and is discharging, then once the current starts the capacitor acts like a battery. The circuit is ...

3

The calculation on page 9 of the PDF is incorrect because of the author's confusion mixing meters and centimeters combined with a numerical error. (Sad!) The correct calculation of the drift velocity for the input values given is $$v_d=\frac{I}{nqA}=\frac{10.0\,\text{C/s}}{(8.48\times 10^{28}/\text{m}^3)(1.6\times 10^{-19}\,\text{C})(3.00\times 10^{-6}\,\... 2 As long as you scale the wire size to always fill the available space for windings, the electrical inefficiencies in a motor stay remarkably constant as you rewind the motor for different voltages. Take two identical motors. Replace the windings in one motor with twice as many turns of wire that's half the area. You'll fill the same space, but you'll need ... 1 In a resistor current flow directly causes a voltage drop so the voltage and current vary together with no lag: eg. if there is a step function of current there is a step function of voltage with no delay between the steps. In a capacitor being supplied with a current, the current supplies the capacitor with a flow of electrons which it accumulates (... 1 A voltmeter is designed to have a high input impedance in order to draw as little current as possible so as not to affect the voltage being measured. The resistance of the leads is so small compared to the internal impedance that changing from Cu to Au will have a negligible affect on the current it draw and therefore negligible affect on the voltage being ... 1 You have probably already learned that when current flows flows through a resistor the temperature of the resistor rises and heat transfers to the environment. So where does that energy come from? It's the kinetic energy that charges continuously get from the electrical potential energy of the source but continuously loses due to collisions with the atoms ... 1 if adding resistance to the circuit causes the kinetic energy of the electron to drop ( potential difference) the speed of the electron after that point should drop The kinetic energy of an electron in an ordinary circuit is roughly constant throughout the circuit and is essentially negligible. Energy in a circuit is not attached to electrons and carried by ... 1 The (drift) speed of the charges in the circuit does not change. You're right that a resistance would tend to slow down the charges. The only way it cannot is because there is an electric field within the resistor that is simultaneously pushing the charges forward. The two forces cancel and the charges keep their speed/KE constant. Think of a block ... 1 Potential at point A is 0,therefore V2=0,because there is no resistance through point A and V2. 1 When we try to emulate DC analysis by putting \omega = 0 , the capacitive reactance becomes infinite, and the inductive reactance goes to zero. That is correct, but it only applies to steady state conditions, that is, where \omega = 0 for a long time. If the frequency is zero for a long time, it is the equivalent of saying you constant voltages and ... 1 To me it is not clear as to the direction of the current i_{\rm ED}. I have assumed that the rectangular boxes represent circuit elements rather than resistors? Referring to the labels on the right hand diagram then for the left hand diagram if one labels the top node b and the bottom node a then v_{\rm b} could be interpreted as v_{\rm ba} which is ... 1 My logic is that the voltage between points D and E is 20, and voltage goes from negative to positive, so D is the negative end and E is the positive end. But$$v_{DE} = v_D - v_E = 20\,\mathrm{V}$$thus$$v_D > v_E Put another way, the voltage $v_{DE}$ is the voltage measured by a voltmeter with the red lead on terminal $D$ and the black lead ...

1

A high-voltage wound motor draws less current for the same power output than a motor wound for a lower voltage. Lower current means less heat dissipation in the power wires leading to the motor, so thinner gauge (and therefore lighter) wiring can be used. In this way a high-voltage electrical system in an aircraft saves on weight. Since the control systems ...

1

The physical basis of KCL is that charge doesn't build up in any region of the wire. And since charge is a conserved quantity that means that for any volume of space within your circuit, the algebraic sum of currents through the surface of that volume must be zero. Since none of the physical assumptions behind KCL depend on the specific arrangement or shape ...

1

This is in response to a point I was making in the comments - that point being that two connections joined by an ideal wire are the same electrical node which means the wire can be 'shrunk to zero length' without changing the circuit. can you illustrate that using a simple picture (it does not need to be perfect) i just cannot imagine it i mean if ...

1

The principle, or, if you want, "paradigm" of instantaneous reactions to forces can be said to reflect Newton's worldview. There was no reason not to assume that a body reacted instantaneously to an applied force. The theory is sufficiently exact to describe phenomena on space and time scales which are neither too big nor to small, and at velocities small ...

1

What would be the alternative? If there was a delay between e.g. force and acceleration, cause and effect, then there would have to be a moment where there is no force and no acceleration. And then the acceleration starts, so the information that a force was applied has to be stored somehow somewhere. This leaves two possibilities: Either you can measure ...

1

The passive sign convention which you have chosen to use is shown in the diagram below. You have put labels on circuit element $X$. The $i$ label with the arrow is the current label. If the numerical value of $i$ is positive that means that current is flowing in the direction shown by the arrow. If the numerical value of $i$ is negative that means ...

1

When an electric current is established in a 1 meter wire, it is NOT every electron travels 1 meter from one end to the other end. It is all electrons simultaneously move at very slow speed of $10^{-6} m/s$. This $10^{-6} m/s$ has nothing to do with the travel speed of electric current in the wire. The speed of current corresponds to how fast can very far ...

1

It's because of drift velocity of electrons. Though the electromagnetic disturbance propagates at somewhat near the speed of light, the actual velocity with which the electrons move is much lower because of collisions with the ions in the lattice and random thermal motion. The electrons can't move fast because they are continuously being slowed down by ...

Only top voted, non community-wiki answers of a minimum length are eligible