What is Capacitor: Definition and 1000 Discussions
A capacitor is a device that stores electrical energy in an electric field. It is a passive electronic component with two terminals.
The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed to add capacitance to a circuit. The capacitor was originally known as a condenser or condensator. This name and its cognates are still widely used in many languages, but rarely in English, one notable exception being condenser microphones, also called capacitor microphones.
The physical form and construction of practical capacitors vary widely and many types of capacitor are in common use. Most capacitors contain at least two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, air, and oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy, although real-life capacitors do dissipate a small amount (see Non-ideal behavior). When an electric potential (a voltage) is applied across the terminals of a capacitor, for example when a capacitor is connected across a battery, an electric field develops across the dielectric, causing a net positive charge to collect on one plate and net negative charge to collect on the other plate. No current actually flows through the dielectric. However, there is a flow of charge through the source circuit. If the condition is maintained sufficiently long, the current through the source circuit ceases. If a time-varying voltage is applied across the leads of the capacitor, the source experiences an ongoing current due to the charging and discharging cycles of the capacitor.
The earliest forms of capacitors were created in the 1740s, when European experimenters discovered that electric charge could be stored in water-filled glass jars that came to be known as Leyden jars. Today, capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems, they stabilize voltage and power flow. The property of energy storage in capacitors was exploited as dynamic memory in early digital computers, and still is in modern DRAM.
If i connect 2 capacitors in series with an AC source ,and an output ,then how exactly will the phase vary with input source ?
A single capacitor makes a 90 degree phase difference with the current,if I don't want that ,what steps can I can take to change the phase difference to 0 ?
Hi. I put the simplest case. A capacitor formed by two flat metal plates faced in the vacuum, with charges of the same absolute value in both plates. In this case, the electric field of the capacitor, in a static situation, has an energy expressed in the following way.
E=\dfrac{q^2}{2 \ C}
Now...
It is given that an uncharged capacitor is connected with a battery. Clearly, it gets quickly charged and flow of current stops in the circuit. What is the reason behind a charged capacitor in completely restricting the flow of current ?
Hi guys..i have got a question...suppose i connect an inductor to a dc source until it is fully charged..as soon as it gets full of magnetic energy,i disconnect it from the circuit..remember that it has magnetic potential energy..suppose an idiot like me opens up the inductor (as inductor is...
Hi,
I am trying to understand capacitors and have come across the example in the attached image.
What I would like to understand is how to calculate the electric field at some distance x within the capacitor. With x>>R , x<R and x=R .
The image is of two circular disks as the...
Homework Statement
What happens if the capacitor plates are pulled farther apart?
Homework Equations
C=Q/V=EoA/d
The Attempt at a Solution
The answer is that the charge stays the same, and the potential difference increases, which results in increased PE.
I saw multiple explanations...
Homework Statement
a) State the boundary conditions for the electric field strength E and electric flux density D at a planar interface separating two media with dielectric constants ε1 and ε2.
b) A parallel plate capacitor with a plate separation d is filled with two layers of different...
Homework Statement
A parallel plate capacitor is made of two flat horizontal conducting plates in a vacuum, each of area A, separated by a small gap. One plate carries a total charge 2Q, the other a total charge −Q. Find the surface charge densities on the four horizontal metal surfaces in...
Homework Statement
This circuit is given:
After the current has stabilized calculate:
1. The current through the voltage source.
2. The voltage and charge on each capacitor.
While the circuit is active and the current is stable, the 4μF capacitor is disconnected from the circuit.
3. What are...
Ok, so I am am trying to make a homemade capacitor that is 4700pf and 15kv. polyester at 125 micrometers thick can withstand 15kv so were good. here is the equation i used
C=ε0 K A / D
Where C = capacitance, ε0 is epsilons constant, K = dielectric constant, A = area of aluminum foil, and D is...
Homework Statement
Homework EquationsThe Attempt at a Solution
The energy stored in the capacitor is ## \frac { CV^2 } { 2 }##. So, this much energy will dissipate as heat. Hence, the correct option is (a).
Is this correct?
It doesn't depend on the shape of the capacitor, right?
I have...
Homework Statement
A proton is released from rest at the positive plate of a parallel plate capacitor. It crosses the capacitor and reaches the negative plate with a speed of 50,000 m/s. What will be the final speed of an electron released from rest at the negative plate?
Homework Equations...
Homework Statement
Find the total amount of energy of a charge (q) initially at rest placed at the left plate of a parallel plate capacitor. The left plate is at V = 0, the right plate at V = V0 and the plates are a distance L apart.
Homework Equations
Etot = 1/2 mv2 + qφ(x).
φ(x) = Vx/L
The...
Homework Statement
A capacitor has square plates of length a separated at a distance d. Dielectrics are inserted as shown in the figure. Find the capacitance
Homework EquationsThe Attempt at a Solution [/B]
I know that I have to integrate, but can't get an expression
Homework Statement
Each plate in the figure has area a and separation d , end of battery is e find charge supplied by battery
Homework EquationsThe Attempt at a Solution . each facing plate will have half the charge supplied by battery, but I am...
The question (and image) that are puzzling me are the same as in https://www.physicsforums.com/threads/two-opposite-polarity-charged-capacitors-in-series.723158/
It says that the capacitors are in parallel, but why? I can´t understand this point, and it certainly seems as if they are in series...
Homework Statement
Find ##i(0^+) ## and ##i(t), t≥0^+##
Homework EquationsThe Attempt at a Solution
[/B]
I'm having trouble finding the current through this capacitor. I tried using a KVL loop for ##t=0^+##, but I'm doing it incorrectly or something.
Earlier in the problem I found...
Homework Statement
https://imgur.com/i5jylxC
Homework Equations
I have to find the charge in each capacitor
The Attempt at a Solution
I don't know how can i start, can i use kirchhoff rule in each loop, using q/C when i go through a capacitor?
Homework Statement
Select the correct expression for ##i_o(t)## for ##t≥0^+##.
Homework Equations
##V(t) = V(∞)+[v(0)-v(∞)]e^{\frac{-(t-t_0}{\tau}}##
##i(t) = C\frac{dV(t)}{dt}##
##\tau = RC##
The Attempt at a Solution
I'm a bit stuck on this problem. Specifically, I'm not sure how to deal...
Homework Statement
The initial voltage on the 0.5 microF capacitor shown in the figure is -20 V. the capacitor current has the waveform shown in the figure. https://i.imgur.com/P8jwI7s.jpg?1
How much energy is stored in the capacitor at t = 870 micro seconds.
Homework Equations
v(t) = 1/c *...
Consider a parallel plate capacitor formed by two plates of length ##L## and width ##d##, separated by a distance ##e##. There is a vacuum in between the plates. Let's note the capacitance of this arrangement ##C_0##.
I insert a conducting plate of length ##l=L/2##, with ##D##, and thickness...
Homework Statement
A parallel plate capacitor has 2 square plates of side l, separated by a distance d (l is a lot bigger than d). Between the plates, there is a linear and non-homogeneous dielectric with constant $$\epsilon_R=1+ay$$ with $$a$$a positive constant. Calculate the electric field...
Homework Statement
In a lab experiment we measured the potential at different points within a cylindrical capacitor electric field modeling plate thing (apparently that's the best I could do to translate that into English). The positive electrode was connected in the middle and the negative...
Homework Statement
Find the voltage across the capacitor given the data underneath the circuit.
Homework Equations
Voltage Divider Rule
Thevenin Equivalent
Ohms Law
The Attempt at a Solution
I have tried using the Voltage divider rule but I can't seem to get the right answer. The correct...
Homework Statement
1. The characteristic decay constant for a capacitor C discharging through a resistor R is the product of R times C. If the initial voltage at time t = 0 is Vo = 13Volts and what is the voltage at time t = 2RC?
2. A capacitor C = 9microFarads is charged from 0Volts to...
Consider a simple circuit consisting of a battery and a parallel plate capacitor .During the process of charging of capacitors, we come to learn that half of the work done by the battery is stored in the form of potential energy and half of it is lost as heat or electromagnetic radiation...
Homework Statement
How long does it take in time constants ( = RC) for the charge on the capacitor in the circuit
shown below to reach one quarter its initial value?
Homework Equations
C=Q/V
time constant=RC
Vc = Vo * (e)^(-t/RC)
The Attempt at a Solution
From C=Q/V
I get
Q=VC
so for the...
Hello guys, came across some Analytical Physics lectures (http://www.physics.rutgers.edu/ugrad/227_f11/classes/lect08.pdf) that got me confused.
It is described in the lecture the problem of determining the force between capacitor plates for a constant voltage (ie. connected to a battery). For...
Homework Statement
Are ALL parallel plate capacitors linear?
Homework Equations
D = permittivity * E
The Attempt at a Solution
Capacitance is linear if permittivity is constant. Is there a case where a parallel plate capacitor is not linear?
Homework Statement
A parallel-plate capacitor is charged to 4850 V. A proton is fired into the center of the capacitor at a speed of v0=2.81 * 10^5 m/s. The proton is deflected while inside the capacitor, and the plates are long enough that the proton will hit one of them before emerging from...
Hi,
I am trying to figure out the peak voltage across a capacitor when charged by 1/2 wave rectified AC. The formula for instantaneous voltage is : Vc=Vs(1-e-t/RC) where:
Vc=Capacitor voltage,
Vs=Source Voltage,
t=time
RC = the capacitor time constant
So I thought I could integrate with...
Hi folks, here's a thought/conceptual question I've been wondering about. What is the maximum theoretical specific energy (IE Joules/kg or equivalent) for energy stored in the electric field of a capacitor? I know the energy stored in a capacitor is given by U=C V^2/2, and the mass of the system...
Hi.
As far as I know, the main reason for using AC in electric power transmission is that voltage can easily be transformed.
If there was a similarly easy way for transforming DC, would power grids work basically the same? To be more specific, how much does AC power transmission rely on the...
Homework Statement
We had a laboration for calculating ε_r in a parallel plate capacitor which we stuffed with plastic plates. All data we picked up was the area A, the distance d (and thus 1/d) and the capacitance C. We are now supposed to use the least squares-method to find ε_r, something we...
I'm trying to understand the difference between these two when it comes to measuring the amount of time they take.
As of right now, my current understanding is that pole relaxation is based on the amount of time that it takes for polarization of the charges to go back to its relaxed state.
For...
This question is from my physics book and neither I nor my teacher can find the mistake in my method. (The original question is not in English so I'll do my best translating it)
> When a coffee maker is connected to the wall (230 V, 50 Hz) its power consumption is 180 W. The power consumption...
Homework Statement
Two parallel plates of metal sandwich a dielectric pad of thickness d, forming an ideal
capacitor of capacitance C. The dielectric pad is elastic, having a spring constant k. If an
ideal battery of voltage V across its terminals is connected to the two plates of this...
Homework Statement
Consider a circuit that consists on a resistor of an intrinsic semiconductor R and a capacitor C in series. The voltage between the terminals of the circuit is U, which is an alternated sinusoidal voltage.
U1, which is the voltage in the capacitor as a phase difference of 30...
I want to calculate Electric field inside and outside a capacitor(two parallel conductor plates and in between a dielectric) which is fed by an AC voltage source. My problem is I do not know how can I relate the electric field to the potential in a capacitor. I got confused about the derivative...
hi, I wonder that inclined plate capacitor formula is the formula in last picture I shared? I am not sure because there are not enough examples about that ?
Homework Statement
Homework EquationsThe Attempt at a Solution
The force between the plates is given by (1/2)QE ,where Q is the charge on the plates and E is the electric field between the plates .
Now Q = CV and E = V/d , where C is the capacitance , V is the potential difference and d is...
Homework Statement
Determine the potential difference across the plates of the capacitor of the network shown in the figure.
Homework Equations
kirchoff's loop rule
q=vc
3. The attempt at a solutio
applying kirchhoffs law
starting at bottom right point,
q/c2-E1+q/c1+E2=0
=>E2-E1=-q/c1-q/c2...
All sites and books give different answers for this question:(
Homework Statement
predict the polarity of the capacitor in the diagram below
Homework Equations
right hand thumb rule
AB is capacitor
The Attempt at a Solution
The side facing south pole becomes south and north facing side...
Hi, I'm trying to form an expression for a rectifier supplying a DC link with current, without actually rectifying a 3-phase input. Usage of the model is really only concerned with the RMS values and the active power drawn from the AC supply.
The DC link is just a capacitor so that:
dVDC/dt =...
Homework Statement
Homework EquationsThe Attempt at a Solution
I have difficulty in solving part (C).
The surface bounded by the Amperean loop is like an open drum.
The current enclosed by the loop is ## I_{en}## = I through the bottom of the drum + I(s) through that part of the curved...
Homework Statement
Homework EquationsThe Attempt at a Solution
Assuming the current is steady,
I = JA, where J is the current density and A is the cross- sectional area
##E = J/\sigma##
Can I take ##\sigma ## uniform here ?
Homework Statement
Homework EquationsThe Attempt at a Solution
A)Clearly,
##V_A - V_B >0
\\V_C - V_D >0## as the current flows from higher potential to the lower potential.
As the time passes on, the potential difference across the capacitor as well as the resistor goes on decreasing...
Homework Statement
Uploaded question(the formula in c part)
And can you tell me in which all cases that formula is used.
Homework Equations
Just want to know where the formula in c part has come from.
The Attempt at a Solution
Sum of magnetic fields due to circular plates calculated and added...
Homework Statement
You charge a parallel-plate capacitor, remove it from the battery, and prevent the wires connected to the plates from touching each other. When you pull the plates apart to a larger separation, do the following quantities increase, decrease, or stay the same?
(a) C
(b) Q...
Homework Statement
A capacitor of capacitance C is charged to a potential difference v from the cell and then disconnected from it. A charge Q is now given to its positive plate. The potential difference across the capacitor is now?
Homework EquationsThe Attempt at a Solution
V is the...