# Questions tagged [voltage]

Voltage is the unit of measurement for electronic potential, from one point location to another.

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731 views

### Back EMF in Motor

Why does back EMF tend to decrease as the rate of doing work increases. When load increases it reduces the angular speed of motor as a result induce current due to back emf also decreases because the ...
44 views

### Potential Difference across capacitor plates [closed]

Energy stored in a capacitor is $\frac{1}{2}CV^2$ . Potential difference between two points is the work done to move a unit charge between them. When $\frac{1}{2}CV^2$ is divided by $Q$ ($Q=CV$) the ...
69 views

### Energy loss through resistors in series

I am trying to understand some A level electricity basics. Unfortunately I stumbled upon a concept that does not seem intuitive to me; this concept goes as follows: for some resistance a charge loses ...
34 views

### What role does voltage play in a simple motor? [closed]

How does voltage affect the current drawn from a battery (say a D cell battery) when using copper coils for a simple motor? What would you use (ex. an equation) to find the affect on current?
114 views

### Potential divider formula

Hi, does applying resistance to a potential divider affect the output voltage? For example, if I were to put resistor R midway across a variable resistor would output voltage still = (R1/R1 + R2) x E? ...
3k views

### Is there a simple proof that Kirchhoff's circuit laws always provide an exactly complete set of equations?

Suppose I have a complicated electric circuit which is composed exclusively of resistors and voltage and current sources, wired up together in a complicated way. The standard way to solve the circuit (...
154 views

### Is this the correct voltage graph of a conducting sphere in the presence of another charge?

This grading rubric show an example of an acceptable answer, however I wonder if the slopes at the surface of the second sphere are wrong. This is a previous AP Physics test question so I'm inclined ...
29 views

### Why $V-Ldi/dt=0$ holds in a pure inductor AC circuit? [closed]

I have read that many author use Kirchoff law to arrive at above result and say that induced emf will oppose the applied emf but I am confused how can it hold in the condition when voltage is ...
73 views

### Induced EMF vs battery EMF

I am bit confused at whether induced emf and battery emf are same in nature differing just in their source. Does a potential gradient exist in case of induced emf as we have when a battery is ...
23 views

### Potential difference across a resistor in a simple circuit

In a physics worksheet that I have, I stumbled upon a simple circuit with a battery (with it's own internal resistance), a voltmeter parallel to the battery, and a variable resistor parallel to the ...
116 views

### Can we speak of an absolute voltage without a convention?

In most practical cases I have seen, voltage was regarded as a difference in electric potential, save the odd change of magnetic flux over time which, as a form of change, also conveys the notion of a ...
30 views

### Magnetic and Electric Field Lines between Conductors

let's consider a system made with 3 conductors: two parallel wires (in this case rectangular wires) and a plane (GND) below them. Consider the following situation in which both wires are connected to ...
30 views

### Convention for expressing voltage between two points

Voltage is always related to two points, because it means a difference in electric potential, between two points. If we want to express the voltage between A and B, we could say: The potential at ...
79 views

### What is the sign of voltage if I move from the positive part to the negative part?

In this example: I want to calculate the voltage that exists between point a and b. Of course this is not about getting some homework done, I really want to understand this. So, this is my ...
25 views

### Voltage in an Inductor

When an inductor is connected with a voltage source we get equal and opposite voltage on inductor against the source voltage. That equal and opposite voltage gradually decreases with time which allows ...
9k views

### Why does a 60W bulb glow brighter than a 100W bulb in a series?

In my physics class I have this problem that shows two lightbulbs, one 60W and one 100W in series, connected to a 120V battery. The problems are: Which bulb is brighter? (A: 60W) Calculate the ...
48 views

### Why should voltmeter have infinite resistance? [duplicate]

My book Isc Nootan 12th reasons for the question that when a voltmeter is connected in parallel and if it had less resistance it would draw some current and potential drop across resistor to be ...
36 views

### Transforming Circuits—adding or subtracting currents?

As shown in the attached image, given Circuit A, we convert the voltage sources to current sources and connect the resistors in parallel, as shown in Circuit B. However, what I don't understand is in ...
100 views

### Why is Ohm's Law $V=IR$?

More specifically, why is R=V/I. I understand what current is; the amount of charge that passes through a point in one second or Q/t. Voltage I'm not as sure, but from my knowledge its the amount of ...
51 views

### Derivation of Diode Current Equation?

$$I = I_0 \left( e^{qV/kT} - 1\right)$$ Diode Equation is given as above which I just always took it as a fact in my electrical engineering class. But now that I have some very basic knowledge of ...
44 views

### Power Ratings—Given a power value and nothing else, how can resistor values be calculated?

I am going through "Circuit Analysis for Dummies". On pg 18, it says, "If you calculate the power dissipated as 0.1 watts, then a 0.25-watt resistor can handle this amount of power. A 0.125-watt ...
137 views

### Different voltage drops depending on the path

I was working through a problem in electromagnetic induction when I discovered that I have a fundamental ignorance of some sort that is puzzling me. Consider a circular wire, at rest, perpendicular ...
3k views

### Charging of a battery

A battery has an Emf 6 Volts. It is completely discharged. It is charged by maintaining a potential difference of 9 Volts across it. If the internal resistance of the discharged battery is 10 ohms, ...
28 views

### Why is there higher voltage drop across larger resistors?

By simple application of $V = IR$, there must be higher voltage drops across larger resistance. However, $V$ is the integral of $E$ multiplied by displacement. Thus, the electric field must be larger ...
159 views

### In a transformer why do we consider the lost voltage to resistance negligible?

In my text book it says: "The induced emf in the primary coil opposes the pd applied to the primary coil,$V_p$. Assuming the resistance of the primary coil is negligible, so all the applied pd acts ...
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### How can current flow in a circuit if back emf is equal and opposite to applied voltage?

Ok, I've seen this question on this site before and other forums as well. A similar argument can be made if a resistor is connected to a voltage source through wires. The voltage across the resistor ...
91 views

### Potential Drop across a Capacitor

Let us consider an ideal parallel plate capacitor in a circuit. The capacitor is connected to a battery which generates a potential difference of V across the terminals. QUESTIONS: 1) The work ...
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### Is the surface of a Perfect Electric Conductor Equipotential in any Condition?

It is known that the surface of a PEC (Perfect Electric Conductor) is equipotential. This is true, in theory, in any situation (equilibrium or not), since the conductor is perfect and so the electric ...
41 views

### Working of potentiometer to measure unknown emf

How at balancing point in a potentiometer does the galvanometer record zero deflection? Why is no current flowing at this point of time in the secondary circuit? Can someone explain what is going on ...
61 views

### Understanding the multipole Expansion for Quadrupoles

Potential of a Quadrupole is given as, $$V(r) = \frac{1}{4\pi e_0}\left(\frac{1}{R}q+\frac{1}{R^2}\sum_{i=x,y,z}\hat{R_i}\vec{p_i} + \frac{1}{R^3}\sum_{i,j=x,y,z}\hat{R_i}\hat{R_j}Q_{ij}\right)$$ ...
1k views

### Measuring the barrier potential of a p-n junction

Is it possible to measure the potential difference across the depletion region (barrier potential) of a p-n junction using a voltmeter?
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### How is the voltage in this parallel circuit different across each component?

I'm studying up on circuit calculations and came across this circuit: I was taught that voltage in a parallel circuit is the same across all components, which would be the voltage supplied by the ...
138 views

### Potential drop in slide wire (Potentiometer Experiment)

While doing the potentiometer experiment I was taught that the galvanometer will show opposite deflection on opposite ends of the slide wire. My questions are as follows: Why does this happen? In ...
212 views

### Trying to understand the electric potential and potential energy

I am trying to understand some facts on electrical potential and potential energy. It is quite confusing in the text to say that the zero potential could be freely chosen for convenience. In that case,...
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### Predicting voltages in RLC series circuits from AC source: differences in order?

Hoping this isn't too homework-like, but I'm missing some sort of concept here. Doing a lab, and I have to use previous data to predict the voltage across the 2nd and 3rd elements (e.g. order is LCR, ...
57 views

### Why aren't salt water batteries used to power cars instead of lithium-ion?

I know salt water batteries are less efficient than lithium-ion, but water is safer, can be found anywhere, is cheap and 100% ecological. Even if it doesn't last long, you can refill anywhere. Why can'...
24 views

### Equipotential Lines

In 2D why exactly do lines of equal potential exist on a point charge at rest? This doesn't make sense to me if the point charge is hypothetically a lone charge undisturbed by other charges.
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### Resistor and capacitor in series

If you put a resistor and a capacitor in series with a 9V battery so that the resistor is in the wire going out from the positive terminal of the battery to a plate of the capacitor. In my opinion ...
357 views

### What happens if I have a square conducting wire being permeated by a magnetic field and the field suddenly disappears?

Suppose there is a square conducting wire in a magnetic field. The two vertical branches will have the same emf, and the two horizontal branches will have 0 emf, resulting in a net emf of zero and ...
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### Kirchoff law of circuit confusing me

I have read that kirchoff first and second rule is in accordance to law of conservation of charge and energy respectively.But I cannot relate how it does justify.KCL just states that incoming current ...
53 views

Can someone please tell me how much 100 mw/ m-1 is converted to v /m? In terms of electromagnetic radiation? I have a gaussmeter that reads about 10-20 volts per meter in one area for electric field ...
37 views

### Analyzing voltage divider circuit with capacitors

Trying to find $V_{out}(t)$ given the following circuit: I wasn't sure how to do it, but my approach was basically find the equivalent capacitance and $v(t) = \frac{It}{C_{eq}}$. $C_4$ and $C_3$ are ...
45 views

### Current and Electricity

Is it possible that a current flows across a resistor although there exists no difference? If yes than how? Is this not a contradiction of ohms Law?
432 views

### How to measure a static electric field?

I looked up google but didn't find any design for measuring electric field that doesn't vary with time. My own idea is to use two parallel plates (like a capacitor but without the dielectric). In an ...
3k views

### Does KV in rc motors (RPM/Volt) tell us anything about the torque?

Considering that KV is RPM/Volt, does it ever tell us anything about the torque? Wouldn't you need to be told the torque separate from the KV rating? If torque can be derived from a KV rating then ...
29 views

### Switching the position of voltage probes changes the sign of the measured voltage. How can you determine the charge sign in a Hall effect then?

When you measure the voltage in a battery, for example, you place the voltage probes at the battery ends and get, let's say, a reading of 1.5V. If you change the position of the probes in regards to ...
34k views

### Why the electric potential of Earth is zero?

For a localized charge distribution the potential is set to zero far away from the charge distribution (at infinity) Now, when grounding a conductor, i.e. connecting it to Earth, it is said that we ...
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### How does a resistor really alter the voltage across it?

This answer sums up the reason why a resistor does not alter the current flowing through it in a circuit. Let's say that we have a $10$ $V$ battery connected with two resistors of resistance $3$ ...