# Tag Info

1 vote

### Don’t understand how nonlinear resistors violate ohm’s law

It seems like this is more of a lack of understanding of the mathematical term "directly proportional", rather than a physics question. Two variables are directly proportional if there is ...
• 8,316

### What is the term "potential difference of voltage" describing exactly?

Near earth gravitational potential is g*h, Potential difference is g(h2-h1) so you can compare Voltage to the difference of height (times g)
• 4,095

### Don’t understand how nonlinear resistors violate ohm’s law

What one refers to as "Ohm's law" is a linear relationship between the current and the potential difference, i.e., (see also this answer) $$V = IR\text{ where } R=const$$ If $R$ is not a ...
• 42.5k

• 9,874
1 vote

### In which cases do KCL and KVL fail to apply in circuits?

I'll focus on KVL. It makes sense to distinguish between "KVL is true" and "KVL is applicable". KVL (shorthand for Kirchhoff's voltage law) is a useful engineering rule inspired by ...
• 29.6k
1 vote

### In which cases do KCL and KVL fail to apply in circuits?

Item #2 in @Dale's answer is specialized to two-terminal circuit elements: it excludes transformers, for example. To include those you must allow four-terminal elements (2-ports) to represent magnetic ...
• 9,909

### In which cases do KCL and KVL fail to apply in circuits?

The assumptions of circuit theory are as follows (see Nilsson and Riedel, Electric Circuits, ch 1): there is no net charge on any circuit element there is no magnetic coupling between circuit ...
• 71.3k
1 vote
Accepted

### Why does this circuit give a quadratic equation for current?

The reason is that the power of the bulb is given and no further information, eg working voltage, working current and working resistance, and so the way the problem is set up only current $\times$ ...
• 81k

### Force on a test charge inside a cell

The potential difference caused by the open state electrodes is cancelled by the ion charge net offset, so the macroscale potential gradient is zero. Otherwise, there would be ion electromigration ...
• 1,679
1 vote
Accepted

### Energy transfer in resistors

In a heuristic Drude-like picture, an electron in a circuit moves from the low potential side of the battery through the circuit to the high potential side of the battery, so when it "moves ...
• 4,782
Accepted

### Derving circuit equations for $RLC$ circuit such that order does not matter

To solve a series circuit, you solve a system of simultaneous equations: one saying that the sum of the voltage drops across all components is zero, and, for each component, an equation relating the ...
• 19.4k

### What is electric potential really a measure of?

Electric potential is defined by the amount of work energy required to move a unit of electric charge from a reference point to a specific point in an electric field.
Accepted

### Electric potential across a resistor

why does the electric potential decrease across the resistor? The short answer is because electrical potential energy is lost as heat dissipated in the resistor. That, in turn, is due to the work per ...
• 58.4k
1 vote

### Proving induced voltages will always cancel in circuit that is in a $B$-field

The induced voltage will definitely not cancel in general. That is the entire point of magnetic induction. Unless you specify that the field is constant and the wires don't move, it is actually quite ...
• 495

### Proving induced voltages will always cancel in circuit that is in a $B$-field

The induce voltage is calculated by the change of magnetic flux, if neither the area nor B changes you have no induced voltage
• 4,095
1 vote

### Inductor connected to an AC source

To formalize all the previous answers, model the switch by a step function: $$H(t) =\begin{cases}0 & t< 0\\1 & t \geq 0\end{cases}$$ And use it to limit the power source to positive t. ...
• 1,625
Accepted

### What is electric potential really a measure of?

I like to think of electric potential as "pressure". By Ohm's law, $$I = V/R$$ Here, $V$ is the potenial difference. The current carrying wire lets in more current, if the potential ...
• 1,805

### What is electric potential really a measure of?

It is a scalar function whose gradient gives the force a charge would experience were it placed at a point. It is a function which measures the change in energy if a charge were to be brought from ...
• 297

### What is electric potential really a measure of?

Electric potential is the ability of a system to perform work on a charge. There do not have to be other charges in the system itself.
• 495
1 vote
Accepted

### Inductor connected to an AC source

Both your equations are correct as they are for different situations with the equation the general one $i=\frac{V_0}{L\omega }(1-\cos\omega t) = \frac{V_0}{L\omega } - \frac{V_0}{L\omega }\cos\omega t$...
• 81k

• 58.4k

### Why $di/dt$ in inductor circuit reduces gradually after closing the switch?

The rate of change of current depends on the inductance of the coil- lots of inductance means the rate changes slowly (for no inductance at all, the rate of change is very high!) and the voltage of ...
• 76.7k

### Why does a Resistor cause a potential drop?

I think it's because the build up of electrons on the (-) side of the resistor (like a damn) more readily fills charge holes reducing potential on that side, meaning, making that area where the ...

### If resistance in an electric current is 0 (ideally) then would there even be current flow?

No, in fact it would be quite the opposite. The current would be so high that all of the voltage would be dropped over the internal resistance of the battery. Thus the terminals would be at the same ...
• 71.3k

### How do signals propagate down unballanced coaxial transmission lines?

Perhaps my idea is not a good answer, but due to the limited size of the comment field, I will put my thoughts here. What you wrote "coaxial cable ... being that both lines have different ...
• 554

### Going through resonance without damping by controlling the coupling between the oscillator and the generator

The main problem I see in your (not)equivalent models is that you start with a forced model and try to find an equivalent model with no external force. Comparison between the original system and the ...
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### Doubling the length of a solenoid doubles its inductance. Two identical solenoids in series have up to four times the inductance due to M. Why?

The formula you're using is an approximation that assumes $l>>r$. But in that approximation, there is negligible mutual inductance, since the flux spreads out at the end on a scale of $\approx r$...
• 6,207
1 vote

### Doubling the length of a solenoid doubles its inductance. Two identical solenoids in series have up to four times the inductance due to M. Why?

But this case is identical to the first case where we simply doubled the length of the original inductor and doubled the number of turns to get $L_{new}=2L_0$ so we have a contradiction. How can this ...
• 42.5k

### Voltmeter in series with a component?

@Jdeep - the voltmeter should read close to the output potential of the cell/battery, assuming the other components in the circuit have a total resistance that is significantly smaller than that of ...

### How do you solve any partial differential equation using equivalent circuits? How is this possible?

Prior to the ascendency of digital computation, analog computers were built for the express purpose of solving big differential equations. You implemented the equation through the use of resistors, ...
• 76.7k

### Current sign convention RC and LC circuits

The difficultly here is that the sign convention used by the OP is not clear. Many Physicists use a sign convention which is dictated by the labelling of the capacitor with the left-hand diagram ...
• 81k

### Surface charge on a current carrying conductor is impossible?

There is another way of looking at the problem that was pointed out in the 1941 paper The Electric Field Associated with a Steady Current in Long Cylindrical Conductor by Alexander Marcus. Like the ...
• 2,761
You are correct and your book is wrong. For a discharge: $$I = -(dQ/dt)_{\rm capacitor}$$ For a charge: $$I = (dQ/dt){\rm capacitor}$$ While the current in the circuit is: I= \int_ \Sigma \...