The study of the presence and flow of electric charge. Charges, currents, fields, potentials.
3
votes
2answers
390 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 ...
3
votes
3answers
162 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
votes
0answers
50 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
124 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 ...
4
votes
2answers
198 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 ...
6
votes
2answers
190 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 ...
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?
0
votes
0answers
51 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 ...
4
votes
2answers
244 views
Sum total distance of electrons on a spherical surface
What is the sum total distance between every possible pair of point charges when there are n point charges on a spherical surface?
All point charges can only and are located on the infinitesimal ...
1
vote
2answers
215 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 ...
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 ...
2
votes
2answers
2k views
Why does electricity flowing through a copper coil generate a magnetic field?
Can some one please explain to me why electricity flowing though a copper coil generates a magnetic field or where I could possibly find that information? Are there other materials that produce a ...
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
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 ...
2
votes
3answers
1k views
How much energy was consumed when we turn on/off light?
My parents told me to turn off the light when I am not using it. But I remember my physics teacher told me that the action of turning on/off a light can cause huge energy. I am wondering how much is ...
1
vote
2answers
695 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
83 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
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
129 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 ...
-1
votes
1answer
199 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
538 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?
2
votes
2answers
194 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 ...
3
votes
6answers
3k views
What causes an electric shock - Current or Voltage?
Though voltage and current are two interdependent physical quantity, I would like to know what gives more "shock" to a person - Voltage or Current? In simple words, will it cause more "electric - ...
4
votes
2answers
444 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
2answers
239 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
1answer
123 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 ...
4
votes
6answers
5k views
In an alternating current, do electrons flow from the source to the device?
If electrons in an alternating current periodically reverse their direction, do they really flow? Won't they always come back to the same position?
0
votes
1answer
65 views
Carrier Electrons Generation and Recombination Time
When a Electron gets promoted to the conduction band from valence band (In generation) lets say for example in Silicon at room temperature.
Is there any way to determine (on average) how long it will ...
2
votes
2answers
270 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 ...
11
votes
2answers
644 views
Does Fire Conduct Electricity? Why?
Recently, I have stumbled upon a YouTube video by Veritasium describing the conductivity of fire. My question is: how exactly does fire conduct electricity? I am a high school student; therefore ...
0
votes
0answers
351 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?
0
votes
1answer
339 views
Finding Current and Voltage through resistors given overall voltage and resistor values
Given a setup like:
Is it possible to find current and voltage through each resistors given resistor values and overall voltage (battery voltage I suppose).
I think $$I_0=I_A=\frac{\Delta ...
2
votes
3answers
66 views
computer vs heater coil comparison
If I have a computer and a heater coil that consume exactly the same amount of energy, which would be more efficient at heating my room? This is assuming that they both have the same fans and heat ...
1
vote
1answer
57 views
Charged plane in an electric field acceleration
A perpendicular plane to an electric field's lines of force has more electric flux than a plane that is in parallel with the lines of force, right?
Does this mean that a charged plate would ...
5
votes
2answers
158 views
What's the difference between Capacitors, Ultra-Capacitors and Batteries
Capacitors are known to hold and release energy very quickly, unlike the slower release that batteries exhibit. If one were to bunch many (1000's of) capacitors together could they function as a ...
1
vote
1answer
112 views
why do lightbulbs sometimes unscrew by themselves?
I've seen some light fixtures which exhibit the behavior of lightbulbs gradually unscrewing by themselves.
0
votes
0answers
75 views
short question - charge [closed]
Four identical metal spheres have charges of q1=-8.0 micro C,q2 =-2.0 micro C, q3 =+5.0 micro C, and q4 =+12.0 micro C.
Three of the spheres are brought together so they touch, and then they are ...
0
votes
1answer
208 views
Resonant inductive coupling and Schumann resonances
I was reading about WiTricity (http://en.wikipedia.org/wiki/WiTricity) a technology developed by MIT to wirelessly transmit electricity through resonance, and I have this question:
Given the ...
6
votes
2answers
1k views
Why does a salt solution conduct electrical current?
How does e.g. sodium chloride (aq) conduct electricity? By accepting electrons (unlikely since they already have a full outer shell)? But they can't be hopping around themselves, can they? I mean, if ...
3
votes
1answer
115 views
Does light induce an electric current in a conductor?
I know that electromagnetic waves induce electric currents in conductors and that's the basis for radio, wi-fi etc.
I also know that light is also an electromagnetic wave. So, can light induce a ...
1
vote
1answer
66 views
Photosensitivity of Photodiodes, lower wavelength -> lower sensitivity?
I saw a diagram of the photosensitivity (Current per Power) of a photodiode.
So there is this diagonal stating the 100% quantum efficiency.
I wondered why the sensitivity for bluer light lower ...
0
votes
2answers
306 views
How can you measure battery output to see if the wattage is accurate? [closed]
When you have a battery and it shows you the milliamperehours and volts. You can use those to calculate the wattage. How can you test the battery to see if its wattage is accurate or if the company ...
0
votes
2answers
288 views
Can a battery charger be too powerful for a rechargeable battery?
I got the impression that a regular iPhone charger can charge the iPhone and the iPhone won't become too hot while charging, and the charging time is standard, but if using the 10W iPad charger to ...
0
votes
1answer
174 views
Faraday's law and superconductivity
According to Faraday's law of induction, volts = -Number of coils in a solenoid * change in strength of magnet / change in time. This doesn't take into account distance or speed, only time. If amps = ...
2
votes
1answer
103 views
Does electric potential have a temperature?
When I took my first thermo class a tucked away chapter introduced Exergy in terms of electrical energy, meaning that the amount of electrical energy you could get from something is functionally its ...
1
vote
1answer
193 views
What kills you: Voltage or Electric current? [duplicate]
Possible Duplicate:
What causes an electric shock - Current or Voltage?
When someone gets electrocuted, what kills them; a high Voltage or a high Electric current, and why?
3
votes
2answers
246 views
How can you have a negative voltage?
How can you have a negative voltage? I don't really understand the concept of negative voltage, how can it exist?
0
votes
1answer
131 views
Finding and plotting the current graph from a voltage graph (piecewise function)
Problem description:
My attempt at making the piecewise function:
Then, in order to find i(t), I took the derivative of 80x/3 and -80x/3, with respect to x, and multiplied C. Obviously, I'm left ...
0
votes
0answers
33 views
Why $Q_{f}$ on glass ~ $12Q_f$ on air in Leyden Jar Expt?
I watching a video lecture on the internet and at at about 46:55 the professor says that the free charge ($Q_f$) on the glass is about 12 times that of air in an experiment with a Leyden Jar. He says ...
1
vote
1answer
146 views
What does the current vs voltage graph of a halogen look like?
I have a halogen light with a tungsten filament. It is rated 500w at 130v but I am running it from an inverter in my car that is putting out 110v. I would like to know what the actual power usage of ...
