What is Potential difference: Definition and 699 Discussions
Voltage, electric potential difference, electromotive force (emf), electric pressure or electric tension is the difference in electric potential between two points, which (in a static electric field) is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage (potential difference) is named volt. In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge). The old SI definition for volt used power and current; starting in 1990, the quantum Hall and Josephson effect were used, and recently (2019) fundamental physical constants have been introduced for the definition of all SI units and derived units. Voltage or electric potential difference is denoted symbolically by ∆V, simplified V, or U, for instance in the context of Ohm's or Kirchhoff's circuit laws.
Electric potential differences between points can be caused physically by electric charge build up or imbalance (eg. well known "static" and electronic capacitor) also by electric current through a magnetic field, and by time-varying magnetic fields (eg. dynamo or generator), or some combination of these three. Additionally on a macroscopic scale potential difference can be caused by electrochemical processes (cells and batteries) and pressure induced piezoelectric effect and heat induced emf across metal junctions. These latter processes at microscopic level have the physical origins previously mentioned. A voltmeter can be used to measure the voltage (or potential difference) between two points in a system; often a common reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy (electromotive force) or lost, used, or stored energy (potential drop).
Moderation Note: Split from the original thread, which can be found https://www.physicsforums.com/showthread.php?p=680746#post680746"
A uniform field does not have potential difference:smile:
Homework Statement
What potential difference is needed to stop an electron having an initial speed of 4.2*10^5 m/s?
Homework Equations
W = delta K
W = q*delta V
The Attempt at a Solution
So I'm pretty sure that the potential difference should be negative in order to stop the...
Homework Statement
Electrons are accelerated from rest through a potential difference of 250000 V. What is the final speed predicted classically?
What is the final speed predicted relativistically?
Homework Equations
KE=0.5mv^2
KE=mc^2-m0c^2
The Attempt at a Solution...
Electrons are accelerated from rest through a potential difference of 277000 .
a) What is the final speed predicted classically? in m/s
b) What is the final speed predicted relativistically? in m/s
Homework Statement
A charge of -3.00 C is fixed in place. From a horizontal
distance of 0.0450 m, a particle of mass 7.20x10^-3 kg and charge
-8.00 C is fired with an initial speed of 65.0 m/s directly toward the
fixed charge. How far does the particle travel before its speed is zero...
Homework Statement
A bird stands on a DC electric transmission line carrying 2800A. The line has 2.5 x 10^-5 ohms resistance per meter, and the bird's feet are 4.0 cm apart. What is the potential difference between the bird's feet?Homework Equations
I wish I knew
The Attempt at a Solution...
Homework Statement
Find the potential difference between two points located at distances R_1, and R_2 from a point source.
Solution
Potential difference = V_{p_1, p_2} = V_{abs_1} - V_{abs_2}.
Question
Hows is the solution above true? What if the angle formed between P_1, Q, P_2 increases...
I understand what voltage is in the context of electrostatics, but the definition of circuits seems foggy to me.
The common definition I see is something like "voltage is the amount of work per unit charge to be done on a charge moving from A to B". However, this is usually in the context of...
Homework Statement
An electric field is given by E_x = (5 kN/C) x^3. Find the potential difference between the points on the x-axis at x= 1 m and x = 5 m. Answer in units of kV.Homework Equations
V = -EdThe Attempt at a Solution
V1 = -5*10^6 N/C * 1 = -5*10^6 volts
V2 = -5*10^6 * 5 = -25*10^6...
Homework Statement
A network below consists of with three bat-
teries, each having an internal resistance, and
five resistors.
http://images.upload2world.com/get-6-2009-upload2world_com_vypln.jpg
Find the magnitude of the potential differ-
ence between points a and b. Answer in units...
Alright before I ask the question I'm going to be pretty blunt, I'm not very good at physics at all. I have a great interest and desire to learn physics but it just isn't very easy for me so explanations are going to have to be pretty detailed and even then I still might not get them...
Homework Statement
A man walks into an electric field with a small charged object that has a charged value of 4.2 E-6C. At a distance of 10m from the object that is responsible for the electric field, he notices a force of 8.0 N on the object he is carrying.
What is the electric field...
Dear all,
can some one help me to solve this question
6 resisitors of resistance 5 ohm are connected to 2 v cell of negligible internal resistance, what will be the pottential difference between terminals, how to slove this
thanks
Homework Statement
On planet Tehar, the free-fall acceleration is the same as that on Earth, but there is also a strong downward electric field that is uniform close to the planet's surface. A 2.00 kg ball having a charge of 5.00 µC is thrown upward at a speed of 20.1 m/s. It hits the ground...
Hello All,
I am wondering why the presence of a dielectric reduces the potential difference of a capacitor (after having been separated from its energy supply). I understand how it works, based around maintaining the same charge, I just don't see why.
Thank you for the Help.
Homework Statement
An automobile has a speed of 30m/s on a road where the vertical component of the Earth's magnetic field is .00008 webers/square meter. What is the potential difference between the ends of its axles, which are 2 meters long?
Homework Equations
The Attempt at a...
Just a few brief questions that my teacher did not answer during the last class:
1) Why is the potential difference at any point inside a charged conducting sphere the same?
2) If a charge were placed outside of a charged say, conducting cube, would the electic field drop off...
Homework Statement
A capacitor has a capacitance of 2.5x10-8F. In charging process, electrons are removed from one plate and placed on the other plate. When the potential difference between the plates is 450v, hoow many electrons have been transferred?
Homework Equations
C=qV
The...
Homework Statement
In a color television tube, electrons are accelerated through a potential difference of 20 000 volts. With what speed do the electrons strike the screen?
mass of electron=9.109*10^-31kg or 0.51099 MeV/c^2
Homework Equations
I don't know which formula I have to use...
Suppose we're measuring the P.D of a parallel plate air capacitor from the inside (i.e from the side the 2 plates face each other), will it be different to when we measure it the normal way (like when discharging it)?
I think it will be more when measuring it from the inside...many times...
potential difference in parallel -- capacitors
Two capacitors C1 = 3 µF and C2 = 9 µF are connected in parallel across a 11 V battery. They are carefully disconnected so that they are not discharged and are reconnected to each other with positive plate to negative plate and negative plate to...
Almost forgot to mention:
This is a DC Circuit!
In the diagram above, find the potential difference across the 3-ohm resistor.
a) 1.3 V
b) 3.0 V
c) 4.0 V
d) 5.0 V
e) 6.0 V
Relevant equations:
So far, I used: I = V/R to find current from the battery.
Then there's E = IR.
(Sorry, LaTeX doesn't...
what are the components to find the magnitude of the electric field strength when only potential difference and that there are two oppositely charged plates that are separated by a given distance.
Homework Statement
For the circuit shown in the figure, find the current through and the potential difference across each resistor. (Figure attached)
a) Find the current through 4.0 ohm resistor.
b) Find the potential difference across 4.0 Ohm resistor.
Homework Equations
V = IR...
Homework Statement
Initially, the switch in the figure is in position A and capacitors C_2 and C_3 are uncharged. Then the switch is flipped to position B. (Figure attached)
a) Afterward, what is the charge on C_1 capacitor?
b) Afterward, what is the potential difference across C_1...
Hello everyone, as you can tell I'm new and just wondering if I could get some help with this question as I'm not sure where exactly I've gone wrong:
Homework Statement
Two wires are used to connect a lamp to a power supply of negligible internal resistance. The potential difference...
Homework Statement
The deflection plates in an oscilloscope are 10 cm by 2 cm with a gap distance of 1 mm. A 100 volt potential difference is suddenly applied to the initially uncharged plates through a 900 ohm resistor in series with the deflection plates. How long does it take for the...
Homework Statement
HELP!
A charged particle is stationary between two horizontal charged plates. The plates are 2.0 cm apart. The particle has a mass of 4.0X10^-13 kg and a charge of 2.4 X 10^-18 C. Find the potential difference between the plates.
Homework Equations
V= EPE/q ...
Homework Statement
Compact "ultracapacitors" are with capacitance values up to several thousand farads are now commercially available. One application for ultracapacitors is in providing power for electrical circuits when other sources (such as a battery) are turned off.
Assume a 1200-F...
Homework Statement
A small electrically charged object is suspended by a thread between the vertical plates of a parallel-plate capacitor. The acceleration of gravity is 9.8 m/s^2.
What is the potential difference between the plates? Answer in units of kV.
Given: tetha = 14 degrees...
Homework Statement
An L-R-C series circuit is constructed using a 175{ \Omega} resistor, a 12.5 muF capacitor, and an 8.00-mH inductor, all connected across an ac source having a variable frequency and a voltage amplitude of 25.0 V.
At the angular frequency in part A, find the potential...
Homework Statement
Through what potential difference should you accelerate an electron from rest, such that it's de Broglie wavelength will be 0.1 nm.
Homework Equations
E = hf
λf = c
The Attempt at a Solution
My Thinking was;
E = hf
E = hλ/c
E= 6.626e-34 * 1e-10/3e8...
Homework Statement
What potential difference is needed to accelerate a He + ion (charge +e, mass 4 u) from rest to a speed of 2.0 * 10^6 m/s?Homework Equations
Kf + Uf = Ki + Ui
U = qV where V is potential difference (volts)
K = (1/2)mv^2
The Attempt at a Solution
I chose the rest point to...
From Electrostatics:
A solid conducting sphere of charge Q is surrounded by an uncharged concentric conducting spherical shell. The potential difference between the sphere and the shell is V. If the shell is now given a charge of -3 Q , what is the new potential difference between them?
I am wondering if I did this right.
Homework Statement
What is the potential difference between the points (x_i, y_i) = (0cm, -5cm) and (x_f, y_f) = (1cm, 4cm) in a uniform electric field equal to E = (20000i - 50000j) V/m ?
Homework Equations
\Delta V = V(s_{f})-V(s_{i}) =...
Homework Statement
A 4.63mF capacitor has stored energy to heat 3.00kf of water from 22 degrees C to 94.5 degrees C. What the potential difference?
Homework Equations
Q= mC delta T
W= Q sq/2C
V=W/C
The Attempt at a Solution
Q= mC delta T
Q= 3kg* 4.184* ( 94.5-22) = 910.02 J...
Homework Statement
An electron with an initial speed of 4.70×105m/s is brought to rest by an electric field.
What was the potential difference that stopped the electron?
Unknown:
potential difference or \DeltaV
Known:
vo=initial speed
m=mass of electron
q=charge of electron...
Homework Statement
The capacitor in Fig. 25-25 has a capacitance of 27 µF and is initially uncharged. The battery provides a potential difference of 118 V. After switch S is closed, how much charge will pass through it? (picture is in the attachment)
Homework Equations
C = Q/V
U =...
Homework Statement
A particle of mass 7*10e-5 kg and charge 1e-6 C from point A to point B a distance of 3 m in the Earth's gravitational field. The kinetic energy of the particle decreases by 5.3mJ during this movement. The acceleration of gravity is 9.8 m/s^2. What is the potential...
Homework Statement
How many 1 microF capacitors connected in parallel would it take to store a total charge of 1 mC if the potential difference across each capacitor is 10.0V?
Homework Equations
C=Q/V
in parallel --> Ceq=C1+C2+C3...
The Attempt at a Solution...
Homework Statement
Givens: ΔV1 = 14 V, ΔV2 = 4.6 V, ΔV3 = 8.8 V, R = 3.0 )
Homework Equations
The Attempt at a Solution
I thought what I was doing was close lol... apparently not. I decided to Combine 10 ohm and 3 ohm into 13 ohms in series with 14V and Combine 5 and 2 ohms into 7...
Homework Statement
A long rod of length L = 7.8 m carries a uniform charge Q = -6.5e-08 coulombs.
Calculate the potential difference VC - VA. The distance c is 4 cm, the distance b is 11 cm, and the distance a is 4 cm. Only part of the rod is shown in the diagram (it is longer than shown)...
Homework Statement
I have two large parallel plates that are conducting and separated by 10.0cm. The charges on the plates are uniform and equal in magnitude but opposite in sign. The difference in potential between the two is 500 V.
The first question concerning this is which plate...
Homework Statement
a uniform electric field has magnitude E = 225 N/C and is directed to the right. A particle with charge +4.3 nC moves along the straight line from a to b.
What is the potential difference Va - Vb between points a and b?
Homework Equations
Potential dif=Va-Vb
The...
Homework Statement
The cyclotron is a device for accelerating charged particles. It requires changing electric fields and a magnetic field, but it can be modeled using (non-physical) static electric fields and potentials as we will do in this problem. Keep in mind that these fields cannot...
An electron and a proton are each accelerated through a potential difference of 10 million volts. find the momentum (in MeV/c) and the kinetic energy (in MeV) of each.
----------------------------
I started by finding the masses of the proton and electron in MeV/c^2, but i don't know where...
Homework Statement
What is the potential difference (in V) between xi = 18.5 cm and xf = 82.2 cm in the uniform electric field Ex = 4920 V/m?
Homework Equations
Not sure?
The Attempt at a Solution
Its simple but I am having problems figuring it out. I have a feeling it has to do...
Problem:
Consider a long charged straight wire that lies fixed and a particle of charge +2e and mass 6.70E-27 kg. When the particle is at a distance 1.91 cm from the wire it has a speed 2.80E+5 m/s, going away from the wire. When it is at a new distance of 4.01 cm, its speed is 3.20E+6 m/s...
Homework Statement
What is the difference between E.M.F. and Potential Difference of a circuit?
Homework Equations
Both have similar SI unit, that is, Volt (V)
The Attempt at a Solution
I did find out one thing, that emf is the potential difference when there is no current flowing...
Consider a coaxial cable with inner radius a and outer radius b. The potential difference between the inner and outer conducter is V. How can it be shown that the electric field at a distance r from the inner conducter is given by:
E = \frac{V}{r ln\frac{b}{a}}
Any help would be much...