# Tagged Questions

The study of the presence and flow of electric charge. Charges, currents, fields, potentials.

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In the diagram below (ignoring the text), does the $V$ mean that there is some electric field outside of this system which results in a potential difference of $V$ between $a$ and $b$ or does it mean ...
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### electrostatics and current electricity

What is the relationship between a closed and open circuits with electromotive force.electromotive force is the force that keeps charge moving in circuit when a potential difference is created.
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### Why do bulbs dim when we switch on TV?

Why do the bulbs dim for a moment when we switch on equipments like CRT television or water pump?
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### Charging with No Current

This may be a basic question, but I am not sure about the exact reason, so I'm asking this I've noticed quite a few times that when you plug an iPad charger to a socket and then switch it on, then ...
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### why do light bulbs explode when in contact with water?

Is it true that when water pours on a light bulb it will explode? If so does this apply to all light bulbs and how does that happen.
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### Does a capacitor experience a Newtonian reaction when being charged?

Say I have a capacitor that is being charged with a battery. There are two wires, one on the positive and one on negative terminal of the battery which go to a capacitor. During the charging, a ...
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### Equation relating voltage and minimum rpm needed for generating 1V using a magnet around copper wire

I was wondering if there is any equation or law or something that relates the minimum rpm needed when a magnet spins around a copper wire to generate 1 volt? In other words, how fast does the magnet ...
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### Difference between potential difference and electromotive force [duplicate]

What is the difference between potential difference and electromotive force? Potential difference is the work done when 1 Coulomb of charge move one region to another.
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### Is it possible to avoid static electricity? [closed]

Sometimes I touch a car or a door and I feel the static electricity in my hand and it hurts sometimes. I try not to touch anything because I feel like I am going to feel this pain again. Is there a ...
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### Ohm's law experiment

I was going through my physics laboratory manual. In the Ohm's Law Experiment, the book states a few precautions without any reasoning. 1.The wire whose resistance has to be determined should ...
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### How can “…electrons flow in metals, but not in the ground…” explain grounding rods?

I really enjoyed Why is the charge naming convention wrong? But, in the comments at the very end, the statement that "...electrons flow in metals, but not in the ground..." left me uneasy. I was ...
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### How does a point charge interact with a Gaussian surface?

A spherical Gaussian surface encloses a point charge $q$. The point charge is moved to to a point away from the center of the sphere. Does the electric field at a point on the surface change? ...
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### Why is a series resistor needed in a simple thermistor experiment? [closed]

I have come across the following simple question, however I can't see any need for a fixed resistor in series. The only possible reason that I can think of is that the resistance of the thermistor ...
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### Why does energy flow between a high voltage transmission line and linemen approaching it on a helicopter?

The video High power line workers shows linemen servicing a live high voltage transmission line. As the helicopter approaches the line, the lineman reaches out with a metallic wand that is ...
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### Capacitor charge and current as a function of type question [closed]

Two capacitors, one resistor and an ideal battery are connected through switches s1,s2 and s3 as shown in figure. Initially capacitor of capacitance 4C is charged, while other is uncharged. The upper ...
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### Resistance of a general resistor [closed]

I have some medium with a resistivity which depends on position. In this material are two electrodes, is there an integral or something which i could numerically integrate to find the resistance ...
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### If we increase dimensions of a wire, how does electron density change?

If we increase the diameter of a wire, does the electron density change at all? When we increase the diameter or the length of a wire (while solving numericals) do we add appropriate number of ...
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### I need proof for dW=eIdt [closed]

I need help to understand from where this equation is formed inorder to continue to study energy stored in an inductor.
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### If increasing applying energy to an atom excites electrons, why does electrical conductivity decrease as temperature increases?

Applying energy to an atom makes the electrons jump up to higher energy levels. This is known as excitation. Electrons on higher energy levels are easier to remove from an atom than those on lower ...
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### Why doesn't a fluorescent lamp implode even though the pressure difference is very high?

According to Wikipedia, the pressure inside a fluorescent lamp is 0.3% of the atmospheric pressure, so the pressure difference between the outside and the inside of the lamp is almost equal to the ...
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### Does temperature have any effect on static electricity?

This is one of those questions that came up during a discussion with a friend on static electricity. His argument (which I dispute) is that there must be a relation between temperature and the ...
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### What happens when the switch in this circuit is flipped? [closed]

what would happen to lights A and B if the switch in this circuit is flipped?
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### How to apply kirchoff's laws to motors in DC and AC settings

DC case: is it ok to treat a motor as a variable resistor, with resistance depending on the load? AC case: suppose I have a motor that runs at 120V AC and is rated to X watts, how can I determine how ...
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### how come if you rub polythene with wool it gains electrons, but if you rub perspex with wool it loses electrons? [closed]

what makes a substance gain or lose electrons when it is rubbed with wool?
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### Some questions related to circuits and flow of electrons

I have some doubts related to electric fields and flow of current. So, let us assume an electric circuit, which contains a battery and a wire connecting positive and negative terminal of the battery. ...
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### Why are there no charges inside a conducting sphere?

Why is it necessarily true that all charges occupy themselves only on the surface of a conducting sphere, and not anywhere inside the sphere? One argument is that if a charge were to be inside a ...
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### Does potential difference or electric field change with distance between parallel plates?

Say you have a set of parallel plates, one is positive and one is negative, if you change the distance between them would electric field strength change or potential difference, given the equation ...
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### Efficiency of resonant inductive coupling as a function of distance

What is the relationship between the efficiency of energy transfer between resonant inductive coupling between two coils, and the distance between the coils?
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### How to increase Resistance of a conductive material?

I'm working on a project that I should measure the resistance of conductive sample ( like brass ). But I've a problem. Resistance of conductive samples is too low which requires a miliohm meter to ...
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### What is meant by “current” in this context?

This is a quote from Optics by Hecht: A stationary charge has a constant E-field, no B-field, and hence produces no radiation—where would the energy come from if it did? A uniformly moving ...
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### Confused about two formulas for electric field magnitudes

So I am going through my notes and I come across these two equations which both describe electric field magnitudes (I think.) $$\frac{k q}{r^2}$$ and $$\frac{Q}{A \epsilon_0}$$ Could someone ...
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### Force on a magnetic dipole due to a magnetic field

Imagine a solenoid which has current $i$ and is producing a magnetic field $B$ which equals $$B=\mu N i$$ Now, imagine we put a small cylindrical magnet at the end of the solenoid. Then because at ...
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### Force Exerting on a magnetic train

A question is already asked ( How does this “simple” electric train work? ). But I've got a question about it. In order to calculate the force which is being exerted on the system including magnets ...
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### How do electrons choose their way through nodes? [duplicate]

Suppose I have a circuit, powered by some emf ($V$). If I put two resistors $R1$ and $R2$ of different resistances in parallel, the current at the node is divided following Kirchhoff's circuit laws. ...
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### Van der pauw method for an isolated hole

Van der pauw method is a way to measure the resistivity of a material with arbitrary shape while it meets some specifications ( being homogeneous and ...). One of the conditions is that the sample ...
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### Do we need wires for current conduction in ionosphere?

As we all know in ionosphere there are free ions and electrons present. So if we somehow take a bulb and a battery in the ionosphere then will the bulb glow due to conducting nature of environment ...
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### Electrons flowing through a circuit make it warm, where does that heat come from

in a circuit I have a low resistance device that consumes many watts, in normal operation this device will get warm; where does this heat come from? the law of conservation of energy states that the ...
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### How to figure out if an element in a circuit is absorbing or delivering power?

. Eg: In the above circuit. 50v source and 0.2Va current source is said to absorb power.If power is absorbed,what work is done with the absorbed power.
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### Which scientist is this?

Okay so I was watching discovery channel, in that i saw a man cleaning live electric wires of 10k volts in the air, he was not touching the ground. They said he was able to do this because of the "law"...
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### Charging by induction

When we charge an conductor by induction and grounding, we first bring a negative charge to the conductor. As a result the mobile electrons of the conductor get repelled and stay far from the negative ...
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### Electrical injuries - Doorknob vs powerline

This is something that has bothered me since high school physics. I have a medical and engineering degree, yet I can't for my life answer this question in a way that's logically consistent in my head....
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### What do we mean by live and neutral wire? [duplicate]

In our household circuit we have ac supply of 50 Hz. It means current reverse its direction in every 100th second. I think then, current flows in one direction then another.Then, why do we have live ...
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### What changes in the electrons before and after a voltage drop?

It is easy to visualize gravitational potential energy as a function of the position of height, and a change in this potential is manifested in a change in height. Further, by the work-energy theorem ...
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### The frequency induced by the alternating current

Let set up the experiment as followed. A string is stretched at two ends. Two magnet poles N and S are placed under and above the string. Now we let an alternating current go through the string with ...
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### Electric field along a wire and load

I have referred to many books and all of them apply loss in potential across a resistor only in case of circuits. However, the electric field is present in the whole conductor. Hence the electrons ...
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### Why does the metal mesh in an electric swatter make a whirring sound?

I have an electric bug swatter that operates on a rechargeable lead acid battery. I had one before that operated on disposable batteries and when it was turned on, it made a high pitched whining noise....
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### Physics Static Electricity [duplicate]

If a person has plastic soles, and are playing on Artificial grass and then the person touches metal goal post, the person will get a static shock.. Why?
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### What will be the effect on coulomb force if any conductor is placed between the electric charges?

I know that if any insulator or dielectric is placed between the electric charges then coulomb force decreases by factor known as dielectric constant.So, what will the effect when any conductor is ...
A typical value for the electron drift velocity in a copper wire is $10^3\ \mathrm{m\ s^{-1}}$. In the circuit below, the length of the copper wire joining the negative terminal of the batter to the ...