# All Questions

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### rectifiers physics fundamental of electronic devices

What value of filter capacitor is required to produce a 1% ripple factor for a full-wave rectifier having a load resistance of 1.5 k"ohms"? Assume the rectifier produces a peak output of 18 V.
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### Why do planets move in fixed orbits?

Is it because the bending of space that occurs around the Sun creates a force acting on the planet which accelerates it towards the Sun (F=ma) while the planet has a tendency to move in a straight ...
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### Quantization in Black Body Radiation [duplicate]

Why does energy need to be quantized to explain black body radiation? Wouldn't the approximate normal distribution of the kinetic energy of particles at a certain temperature be sufficient, ie. few ...
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### Finding the initial velocity of projectile

What is the formula for calculating initial velocity of projectile using the conservation of energy given the mass, height, angle ?
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### Fluid flowing into small pores

I have some open porous foams with pore sizes ranging from 50-100nm. I want to flow water into this structure but even at 30 atmospheres it would NOT go in. I am looking for a way to calculate the ...
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### Why does this not make infinite energy?

Here's an idea I had for infinite energy: Get into a spaceship, and fly to a star or other large body and get into orbit. Then just harvest your kinetic energy somehow and keep going indefinitely. My ...
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### Are Q1 and Q2 attracted or repelled to the sphere shown in the figure below?

Can you tell from the image below if Q1 and Q2 are attracted or repelled. Will Q2 only be attracted to the sphere if Q2 is enough bigger than Q1? Will the positive charge inside the shell attract ...
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### How do you calculate the magnitude of the light waves emitted from an LED?

Question is in the title. My goal is to see if this is enough to make an interferometer using a surface-mount photodetector.
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### What is the exact meaning of homogeneity in cosmology?

I understand that, in general, homogeneity is the physical attribute of being uniform in composition (" of the same form at every point"), but I'm slightly confused when it is used in cosmology as ...
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### Finding the frequency of vibration of part of a system

The setup: 4 spheres of diameter 1 are suspended on a horizontal plane (magically). They are arranged in a square with length one. The velocity of a wave in the medium they are suspended in is equal ...
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### Non zero accetion, varying speed

Can an object have non zero acceleration without having varying speed? How? Can you explain with an example please.?
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### How does one express a Lagrangian and Action in the language of forms?

In Lipschitzs Classical Mechanics a Lagrangian is defined as: $L(q,q',t)$ for some trajectory $q(t)$ of a particle And the action is defined as: $S:=\int^a_b L(q,q',t) dt$ How does one ...
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### Max speed of a turning disk for an object to stay at rest

A coin is at rest relative to a disk moving with a angular speed of w: The coin weighs 0.010 kg The distance of the coin to the center of the disk is of 0.20 m The static friction is of 0.45N ...
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### Why does the water bottle not rotate when it is half full?

Consider this water bottle: When it is full and thrown up in the air, it rotates at a constant velocity. When it is less than 1/8th full, the water bottle rotates even faster than when it was ...
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### Can a microwave oven induce an accumulation of static charge in food?

I often "touch test" microwaved food to see if it is heated up enough to my preference. In doing so, I sometimes notice the characteristic tingle of a static discharge between the food and my finger ...
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### Finding the magnetic field [on hold]

A mechanical pendulum is made of a metal rod, one end of which is attached to a string. The mass of the rod is $m$ and the string length is $l$. The oscillation period of the thus obtained pendulum ...
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### Why there is no mention of Archimedes Principle in whole Fluid Mechanics? [on hold]

Why there is no mention of Archimedes Principle in whole Fluid Mechanics? Without Archimedes, today we can't see Boats & Submarines.
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### from control torque to magnetic moment

I am designing a system which generates a magnetic field to make itself move in space (a cubesat with magnetorquers). This magnetic field is known as the magnetic control torque, i.e. it will torque ...
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### What does it mean when we say that power of a bulb is 10 W? Since $V/I=$ resistance is a constant, how can power $=VI$ be a constant?

My question is simple. In Ideal situation, at constant temperature, we know that normal appliances like a filament bulb has straight Voltage vs Current graph, meaning its resistance is constant or ...
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### Velocity Selective Coherent Population Trapping and recoil limit on temperature

I have read that it is possible to go under recoil temperature limit using VSCPT (Velocity Selective Coherent Population Trapping) and that this method is based on atoms trapping in quantum state in ...
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### The significance of the pressure term within the momentum-energy tensor [duplicate]

EDIT: this question is based around my notion regarding the possible role of potential energy in the momentum energy tensor T$_{\mu\nu}$, The answer below resolves the question and I have deleted ...
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### Need help in understanding tensorial simplification in a special case

The Lagrangian of N=2 supergravity's important terms for my purpose are (hopefully I simplified this correctly): ...
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It sounds like a joke but I just want to know if shadows have mass, since shadows are formed when there is blocking of light. It forms a black pattern with no energy therefore it has no mass.
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### Books on quantum mechanics with intuition [duplicate]

So, I know that there are a lot of questions about good books on quantum mechanics and I have read each one of them, and I go on and bought Griffiths' Introduction to Quantum Mechanics. But the fact ...
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### Initial current, RC Circuit

The task goes like this: The voltage between the points A and B, in the circuit diagram below, is 100 V. What's the initial current through the resistor when we close the switch S? (Other components - ...
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### Finding displacement of spring [on hold]

Q) A block lies on a horizontal frictionless surface, and the spring constant is $50\,\mathrm{N/m}$. Initially, the spring is at its relaxed length and the block is stationary at position $x=0$. ...
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### Molecules from atoms [migrated]

Why does two oxygen atoms combine to form a molecule and not 3 or 4?Also why does one sodium and one chlorine atom combine to form NaCl while two chlorine atoms are required to combine with one ...
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### The minimum force required to lift a triangular prism

If I have an isosceles triangular prism of mass m with the angle at the top being $2\theta$ I want to work out the minimum force I would need to apply to the upper faces to lift the prism. Lets say ...
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### Solving the Three-body problem numerically

I want to create a program in $Mathematica$ that solves numerically the Three-body problem by Euler-Lagrange's equations. I was searching some methods to sucessfully do it. So I found a way to solve ...
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### Scattering and form factor

In Introductory Nuclear Physics by Krane (there's a PDF online), it is mentioned electron scattering on the nucleus to get a picture of the latter's shape, e.g., its radius. It is said the probability ...
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### How can electric field accelerate fog dissipation?

I should emphasize that I view the problem as a 'research' rather than a 'textbook' level. However, as I am almost unfamiliar with the subject it may be that the answer is elementary and well-known. ...
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### Voltage and volume, same SI symbol, how to discern between the two? [on hold]

Both are SI quantities that use the same symbol, namely $V$. It annoys me that I might be working with the wrong unit even though it's easy to see if it's voltage or volume by looking to the whole ...
### Why are $W$ bosons massless above electroweak scale? [duplicate]
Because of the Higgs mechanism, one must replace the Higgs field $\phi$ with $\phi_0 + \phi_1$ where $\phi_0$ is the vacuum expectation value. As far as I understand, the $\phi_0$ gives the mass term ...