What are three possible locations at which the electrostatic potential of a point can be defined as having a value of zero?

Two 53.0 x 10^-9 C point charges are located on the x axis. One is at x = 0.35 m, and the other at x = - 0.35 m.

a) A third identical charge is placed on the y axis at y = 0.35 m. Find the magnitude of the force acting on this third charge? Answer in Newtons.

b) Now the third identical charge is placed on the y axis at y = 2 x 0.35 m. Find the magnitude of the force acting on this third charge? Answer in Newtons.

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Four charges are placed at the corners of a square. The side of the square is a = 0.30 m.

a) If the charge are identical and positive q = 21.0 x 10^-9 C what would be the magnitude of the force acting on each of the charges? Answer in Newtons.

b) We change the charges by q₁ = 21.0 x 10^-9 C, q₂ = 11.0 x 10^-9 C, q₃ = -12.0 x 10^-9 C, q₄ = -31.0 x 10^-9 C. What would be the magnitude of the force acting on charge q₃? Answer in Newtons.

c) We place the same charges at the corners of a rectangle of sides a and b (instead of a square). If b=2a/3 what would be the magnitude of the force acting on charge q₃? Answer in units of Newtons.

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Two 2.20-?C point charges are located on the x axis. One is at x = 1.57 m, and the other at x = -1.57 m. Determine the magnitude of the electric field on the y axis at y = 0.530 m. Answer in units of N/C.

During the Apollo XI Moon landing, a retroreflecting panel was erected on the Moon's surface. The speed of light can be found by measuring the time it takes a laser beam to travel from Earth, reflect from the panel, and return to Earth. If this interval is found to be 2.51 s, what is the measured speed of light? Take the center-to-center distance from Earth to Moon to be 3.84 X 10⁸ m. Assume that the Moon is directly overhead and do not neglect the sizes of the Earth and Moon. (Assume the radius of the Earth and the Moon are 6380 km and 1740 km respectively.)

Two identical objects each hold a net charge of q = 2e. If the gravitational force between the two objects exactly cancels the electrostatic force between the objects, what is the mass of each object?

According to Hubble's law, light and other kinds of electromagnetic radiation emitted from distant objects are redshifted. The more distant the source, the more intense is the redshift. Now, the expansion of the universe is expected to explain the redshift and its nearly linear dependence on distance between source and observer. But isn't there an other source influencing the redshift? We know that a light beam passing the Sun is deflected by the Sun's gravity in accordance with predictions made by Einstein's general theory of relativity. This deflection is dependant on a gravitational interaction between the Sun and the light beam. Thus, the position of the Sun is affected by the light beam, though by such a tiny amount that it is impossible to detect the disturbance of the Sun's position. Now, during its journey to the Earth a light beam, originating from a distant source in the Universe, is passing a certain amount of elementary particles and atoms. If the light beam interacts gravitationally with those elementary particles and atoms, affecting the microscopic mechanical properties of the individual elementary particles and atoms at issue, can this interaction be detected as a redshift of the light beam? If so, could we use this gravity redshift to measure the mean density of matter and energy in space? The beginning of the sentence "If the light beam interacts gravitationally with those elementary particles and atoms..." should be interpreted to say "If the light beam interacts gravitationally with those elementary particles and atoms by way of leaving them in a state of acceleration different from their initial state of acceleration...." This clarification seems to necessitate the additional question: "why would a gravitationally interacting object (a cluster of photons) passing another gravitationally interacting object (a mass) leave that mass in the same state as before the passage?"

Atomic and molecular spectra are discrete. What does discrete mean, and how are discrete spectra related to the quantization of energy and electron orbits in atoms and molecules?

I read this artice: Physicists Prove Einstein Wrong with Observation of Instantaneous Velocity in Brownian Particles

There is a common analogy about the structure of an atom, such as the nucleus is a fly in the centre of a sports stadium and the electrons are tiny tiny gnats circling the stadium (tip of the hat to 'The Greatest Show on Earth') but what is in the space between the 'fly' and circling 'gnats'?

Differences? They are both an electron and a proton, since the neutron decays to a proton and an electron, what's the difference between a neutron and proton + electron? so is it just a higher binding energy between the two?

if i understood this correctly, the determination of voltage for a specific voltaic (gallvanic) cell is determined only by the chemical correlation between the two metals. is this true? for an example , if i use iron instead of zinc in the example from wikipedia, i will get a different voltage?

It's a well known fact that an observer that accelerates at a constant rate from ?c at past infinity to +c at future infinity sees a horizon in flat Minkowski spacetime. This is easy to see from a spacetime diagram once you realize that the union of past light cones on such a trajectory has a boundary that divides the spacetime into two regions - one inaccessible by the accelerating observer.

This leads to the classic result of Unruh radiation when one looks at the quantum field theory for such an observer. The horizon plays a crucial role here.

How does one go about determining whether a horizon is seen by a general class of worldines? In particular, is there any reason to believe that a horizon would exist for an observer that is stationary for all time except for a finite period of acceleration and deceleration?

Is there any other class of worldlines other than an indefinitely accelerating observer for which a horizon is known to exist in flat spacetime?

Something that has bothered me for a while regards the interpretation of chemical potential for different statistics. While I understand its meaning in metals (and its relation with the Fermi surface), I cannot quite relate this definition with the thermodynamic chemical potential, defined as the change in energy of the system when one particle is added to it (or according to Wolfram Demonstrations, " It can be interpreted, for example, as the ability of the system to perform phase transitions or chemical reactions, or its tendency to diffuse").

1) Are those concepts (thermodynamic vs Fermi-Dirac chemical potential) related or they should be thought as different things?

2) Am I missing something trivial or this cited demonstration is misleading? It is mentioned there that the x coordinate corresponds to (E-u). Shouldn't the function blow up for x = 0 independent of temperature, then? I do not understand the shift for negative values as temperature increases.

Quick question for the nuclear engineers/physicists out there

Where does I-134 come from? I cant find it in any of the charts of standard decay products of Uranium fission, but there is tons of the stuff in Fukushima reactor 2 building right now (2900 MBq/ml of water! Nasty!)

half life is 52 minutes, so either it is being made by fission (which would be bad news) or something from weeks ago is still decaying into it in large quantities.

What practical application can we expect from particle physics a century or two from now? What use can we make of quark-gluon plasmas or strange quarks? How can we harness W- and Z-bosons or the Higgs boson? Nuclear physics has given us nuclear plants and the promise of fusion power in the near future. What about particle physics? If we extend our timeframe, what promise does string theory give us? Can we make use of black holes?

Or to put the question another way - what is the result of a proton-positron collision, or an up quark-charm antiquark collision, etc.? As far as I know, annihilation happens only between particles of opposite charge and same mass, but perhaps I am wrong?

And if the types of annihilation mentioned above cannot happend, what are the reasons?

Thank you.