The study of the presence and flow of electric charge. Charges, currents, fields, potentials.
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4answers
579 views
Why there is no “Edison” unit in physics? [closed]
In the popular culture the XIX-XX century competition between Thomas Edison and Nikola Tesla is well-known. The example could be the Prestige movie, where there are some "Edison's agents" who sabotage ...
4
votes
1answer
115 views
How much of current flows through a bird sitting on a power line?
I've been googling for hours and went through over a hundred answers. Now, some say the bird doesn't form a closed loop, some say the current is so small that it doesn't kill the bird. From as much as ...
0
votes
2answers
153 views
How does current flow from the emitter, through the base and to the collector in a NPN transistor?
So, I understand that for a NPN transistor to work the emitter-base junction needs to be forward biased and the collector-base junction needs to be reverse biased. I understand how current flows from ...
1
vote
1answer
66 views
Can someone explain this intuitively please?
In a static situation we defined voltage as energy/unit charge, or j/c. As the distance between the charged particles increased, the voltage decreased. Now why do we not apply this in a simple DC ...
0
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1answer
33 views
Is there a material that changes local conductivity
I hope this is the right forum to ask this question. Is there a material (preferably thin, like a membrane) that changes its local conductivity (by that I mean the permeability for an electric field; ...
0
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0answers
45 views
Really Confused about Drift Velocity [closed]
I'm having a really hard time understanding drift velocity
A current of 10.0A is carried by a copper wire of diameter 1mm. If the density of the conduction electrons is 8.47 x 102m-3, how long does ...
0
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1answer
115 views
How electrons act under rotating magnetic field?
I study Power Engineering in University. Today I asked my lecturer to explain me exactly how atom's electrons act under spinning rotor's magnetic field, that generated dynamic electricity. But he even ...
1
vote
1answer
56 views
Reducing deposition on power supply wires
From my house there are two wires, i.e. a live and a ground wire which are placed on the power supply lines by a hook. They are not tightly jointed because of some reasons. These two wires are also in ...
0
votes
1answer
78 views
If we connect a block of p-type semiconductor only to a positive terminal, will it become positively charged?
Connect the positive terminal of a battery to a piece of p-doped semiconductor, say, silicon doped with boron. Will the terminal pull electrons out of the doped silicon, or equivalently, inject holes ...
1
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1answer
43 views
What happens when a compact fluorescent lamp implodes?
When a incandescent lamp implodes, the filament burns up and the current is interrupted.
Yesterday, a compact fluorescent lamp imploded and blew all the switches / fuses. I'm not sure if the same ...
4
votes
3answers
577 views
Why is AC more “dangerous” than DC?
After going through several forums, I became more confused whether it is DC or AC that is more dangerous. In my text book, it is written that the peak value of AC is greater than that of DC, which is ...
4
votes
1answer
60 views
Thermal conductivity affected by electrical current
Does anyone know of any materials whereby the thermal conductivity can be changed by passing an electrical current through the material?
0
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1answer
111 views
Does the electric field inside a sphere change if point charge isn't in center?
As i understood , if you have a point charge in the center of a hollow conducting sphere then the electric field inside it, is zero because the charge distribution is spherically symmetric.
But ...
3
votes
1answer
101 views
Is it possible to get energy from electrical wire using induction?
Pardon me if this is a stupid question but my physics courses are from a long long time ago and I was a teenager back then. ;)
Electricity in a wire generates electromagnetism, right?
Would it be ...
2
votes
1answer
122 views
Calculating engine starter’s energy use
During a discussion on start-and-stop vehicle technology some bloke began pushing the point that re-starting the car uses stored energy from the battery, which needs to be replenished by increased ...
1
vote
3answers
151 views
How exactly does a resistance reduce current?
I've heard that resistors are used to decrease current to a particular appliance, such as in the regulator of a fan. However, I've also heard that the total current in a circuit is always the same- in ...
1
vote
0answers
29 views
pressure required for displacing a single electron off a crystal
I need to know this for my project- "power generation using the pressure applied on a keypad of a mobile electronic device". How much pressure does it take to displace a single electron off its ...
5
votes
2answers
290 views
What causes fluorescent light bulb to light up when it is near a plasma globe? Can this phenomenon be used to generate electricity in a circuit?
When a fluorescent light bulb is placed near a plasma globe, despite the fact there isn't a closed circuit, a part of the light blulb would light up.
I tried measuring the voltage of the air ...
3
votes
2answers
75 views
What happens to this potential energy?
Let's say I turn on a Van de Graaff which creates a large positive charge. Now let's say I have an object with a positive charge in my hand and I start walking toward the Van de Graaff from $x$ meters ...
1
vote
1answer
97 views
Am I properly identifying the resistor terminal voltage?
The frequency applied to a circuit of voltage 120 V with a real coil and a resistor has a value of 50 Hz. The resistance of the resistor is 10 $\Omega$. The voltage at the resistor terminals ...
1
vote
0answers
27 views
Microscopic fields inside a conductor
In a neutral conductor if we assume electrons as point charges, the electric field in the space between them cannot be identically zero. This microscopic field may be very weak. What if we were very ...
0
votes
0answers
43 views
Object accelerated by electromagnet
If I have an electromagnet (powered by a battery) and a metallic object, the
power generated will depend on the voltage of the battery and the resistance of the coil.
If I accelerate the object, will ...
3
votes
3answers
164 views
Why is electrical energy so difficult to store?
Does anyone know a general answer to these questions? (I've asked them together because they're all pretty related, it seems.)
Why is it that we find electrical energy so difficult to store? Do we ...
0
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0answers
52 views
What is the value of the equivalent resistance? [closed]
Can anyone tell me the value of the equivalent resistance for resistors R7, R8 and R9 in the following image?
Circuit -> { http://www.mediafire.com/view/?ktct310wyvezf2x# }
0
votes
2answers
128 views
Why the CFL light bulb flashes even if there is a power cut?
Today when there was a power cut I saw that the CFL light bulbs were flashing time to time at regular interval. I was amazed as there was no source of power to the CFL bulbs even they were flashing as ...
0
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0answers
53 views
Why it happen's when I rub my finger's?
I have a pc with a metallic body on my CPU case. Yesterday suddenly the earthing wire of my CPU broke down and I was able to feel a little bit current on touching it's metallic body. But what I found ...
2
votes
2answers
309 views
Round bulb and Long bulb in Series Circuit
If you have a series circuit with a battery, one round bulb (with thicker filament), and one long bulb (with thinner filament), the round bulb does not light up and only the long bulb lights up.
...
0
votes
0answers
41 views
AC source and the capacitor [closed]
An AC circuit is connected to a capacitor. Will the rms current increase, decrease or remain constant if the dielectric slab is inserted into the capacitor?
3
votes
2answers
420 views
Capacitor circuits with light bulb
Let's say we have a normal circuit with a light bulb, with wires and a battery.
When one places a capacitor in this circuit, how is the light bulb able to light up, even when the capacitor prevents ...
2
votes
1answer
76 views
What exactly causes an increase in resistivity?
Explain in terms of charge carriers why the resistance of copper is less than that of CuSO4 solution, which is less than that of hydrogen gas
This is the question directly asked for homework, and ...
1
vote
2answers
222 views
Electric potential at a point outside a charged sphere
The question asked me to find the potential at a distance $r$ from the center of a charged sphere, where $r>r_0$ of the sphere.
Actually, the question is answered, but what is confusing me is ...
1
vote
2answers
57 views
Starting vehicle on hot days
Why it is easy to start the vehicle on hot day than on cold days?
Since on winter days it is diffcult to start than on hot days I thought it is due to the low temperature which in turn affects the ...
1
vote
1answer
114 views
The field of uniformly charged ball (without Gauss theorem)
The solution of Poisson equation is given by
$$
\mathbf E = \int \frac{\rho (\mathbf r )(\mathbf r_{0} - \mathbf r )}{|\mathbf r_{0} - \mathbf r|^{3}}d^{3}\mathbf r.
$$
I tried to use this term for a ...
1
vote
2answers
765 views
Physical interpretation of y-intercept in a Current vs Voltage graph
So I collected current and voltage data from a simple circuit with a power source and a resistor, using a multimeter. I created a graph for this data using excel and got the y-intercept (which is ...
3
votes
1answer
85 views
Why does electromagnetic waves travel slower in well isolated conductor?
Wikipedia writes, that
Propagation speed is affected by insulation, so that in an unshielded copper conductor ranges 95 to 97% that of the speed of light, while in a typical coaxial cable it is ...
4
votes
2answers
201 views
How does lightning “know” where to go?
If lightning comes down in, say, a large flat field with a lightning rod sticking out of the middle, the lightning will strike the rod.
How does it "know" the rod is there?
Will it always strike the ...
4
votes
3answers
143 views
If an electric car were to drive without having to stop, would the range be greatly affected by the speed at which the vehicle is moving?
Of course aerodynamics factors into this question, and the faster you are moving the more air you have to push out of your way, the more energy you use. But would the difference be only a small ...
0
votes
4answers
136 views
Why is there a potential difference?
The question then asks for the potential difference between $X$ and $Y$, which is claimed to be $3.6\text{ volts}%$.
Why would there be a potential difference in this case? If I connect a lightbulb ...
2
votes
1answer
88 views
Which of these two methods is correct for calculating current?
I recently came across a question, for which I saw two possible methods of finding the solution. I was required to calculate the "current flowing" $I$ when given the voltage $V$, frequency $f$, total ...
2
votes
2answers
158 views
Using Electrostatic Force to Repel Dust From an Object
I have two 4,000V, 2.5mA, DC power supplies and am attempting to use them in such a way to cause a 6x4x1-inch ABS plastic object to repel dust from the ambient air and prevent this dust from settling ...
-1
votes
1answer
206 views
Can I use AA batteries to charge iPhone? [closed]
Technically, 4 AA batteries will give out ~5V, which is equivalent to USB. Can you use 4 AA batteries to charge an iPhone, without messing up the Li-Ion cells used on iPhone?
So my question really ...
2
votes
2answers
581 views
Ohmic and Non-Ohmic devices
Why do some conductors follow Ohm's law and some do not? Isn't there any universal law that can explain the flow of current?
6
votes
2answers
193 views
Ionized Depletion Region, Why aren't those charged being excited?
Ok so I understand the PN junction, and how when 2 Semiconductor materials are placed together the Electrons will jump into the Holes near the junction creating a Negatively Ionized Atoms on the ...
2
votes
2answers
207 views
Why does the current stay the same in a circuit?
I was informed that in a circuit, the current will stay the same, and this is why the lightbulbs will light up (because in order for the current to stay the same, the drift speed of the electrons need ...
4
votes
2answers
497 views
What happens to capacitor’s charge when the plates are moved further apart?
In my physics textbook there is an example of using capacitor switches in computer keyboard:
Pressing the key pushes two capacitor plates closer together, increasing their capacitance. A larger ...
1
vote
1answer
124 views
Finding the Electric Field (and other information, besides)
The problem I am working on is:
Two parallel plates having charges of equal magnitude but opposite sign are separated by 29.0 cm. Each plate has a surface charge density of 33.0 nC/m2. A proton is ...
2
votes
2answers
279 views
Higher To Lower Electric Potential
The question I am working on is:
"An electron moving parallel to the x axis has an initial speed of $4.65 \cdot 10^6~m/s$ at the origin. Its speed is reduced to $1.27 \cdot 10^5 ~m/s$ at the point ...
0
votes
0answers
361 views
How to find the equivalent resistance for the following circuit? [closed]
How do you find the equivalent resistance for the above circuit, if current is entering via A and leaving via C? Can it be done by treating it like a wheatstone bridge?
1
vote
2answers
250 views
Why and how does symmetry work in circuits?
Why symmetry work in circuits? In my book there is no mention explanation as such for symmetry arguments and circuits. But there are circuits that are very difficult to solve without symmetry. Also I ...
1
vote
2answers
103 views
Under what condition charges do not flow in closed circuit?
I wanted to ask under what conditions will charges not flow in a closed circuit. Or when is current through the circuit zero even when an EMF is applied?
Like in the case of potentiometer, we say that ...
