# All Questions

136,345 questions
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### Explain why the magnets move towards eachother in this setup

I have two bar magnets (actually stacks of small magnets, but I believe they should behave the same) attached to a stack of (presumably conductive) coins, and not diametrically opposite. When I ...
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### Light path in a Schwarzschild spacetime

This might be a silly question for the physicist as I'm not one but I've have watched this YouTube video which shows the steps needed to simulate light path in a Schwarzschild spacetime, what I failed ...
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### A (probably silly) doubt regarding motion of bar magnet

So my instructor was teaching electrodynamics the other day, and he analysed the electric and magnetic field of the bar magnet moving with velocity v in x direction, first from the ground frame and ...
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### Materials with good thermal insulating properties

I'm doing a research for a university project. In particular I'm looking for a "commercial" material (so a material that is available on the market or can be home made) that has good thermal ...
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### What is an axial and polar vector?

Can someone please explain this type of vector to me, I can not understand it. Axial vectors have an inner orientation, i.e. the direction of the vector indicates the positive orientation. For ...
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### Uniqueness Theorem and the 1D Infinite Square Well

Consider the 1D infinite square well problem: $$\frac{d^2\psi (x)}{dx^2} = -k^2\psi (x)\tag{1}$$ along with the boundary conditions $\psi (0) = \psi (L) = 0$. This seems to be a well posed problem ...
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### Difference between DC and AC liquid resistivity measurement

If I was to try and measure the resistivity of an insulating liquid (>10^14 ohm.cm), which type of voltage should i apply, AC or DC, and why?
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### Angular collision equations help

The situation is a particle of mass m striking a rod of the same mass and length $L$ at an angle with an initial velocity $v$ elastically. Now to describe this situation I wrote the following ...
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### Current in the Photoelectric Experiment

A photocell is connected in series with an ammeter such that the collector is connected to the negative terminal of the battery (emf > 0). Therefore there exists a stopping voltage between the anode ...
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### MOSFET Body terminal

What is the point of the body terminal in a MOSFET. If we assume Vsoure=0, Vdrain>0 then we will have a linearly changing voltage from drain to source. Then if Vgate>0 , depending on the difference ...
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### Einstein's thought experiment about a train

Observers: - person 1 on the train - person 2 on the ground person 1 sees the two lights instantly person 2 sees person 1 at 2 different instances based on their position person 1 would see person 2 ...
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### Rotation matrix product and angular velocity

I'm solving the following problem from the book "Analytical Mechanics for Relativity and Quantum Mechanics" by Oliver Davis Johns: Let $R(t)=R_a(t)R_b(t)$ be a rotation matrix. Show that the ...
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### Bernoulli question from a layman

So my understanding is that pressure and velocity are inversely proportional. If I where to go from an 8" pipe to a 4" pipe the velocity would increase thus a decrease in pressure. Pretty straight ...
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### How can sunlight cause skin cancer? [on hold]

If the atmosphere absorbs the UV wavelengths, then what’s left is visible, IR and maybe a really small amount of UV that transmits it’s way to earth. IR and visible are non ionising, so is it the case ...
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### Speed of a video and Doppler effect

While watching videos at 1.5x or 2x the original speed I often notice a change in the speaker's voice. I am not sure if that is a change in pitch or something else, and was thinking how it could ...
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### Explain why the angle of incline of the ramp affects friction between the surface of the ramp and the object [on hold]

Experiment: the object is placed on the ramp and the angle between the ramp and the floor is changed.Explain why the angle of incline of the ramp affects friction between the surface of the ramp and ...
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### Stability of a 10km planetoid with a micro-black hole in its centre

Let's assume there is a tiny, 10km-radius planetoid with a micro-black hole in its centre of about 10^19kg, so the surface of the planetoid is at 1g. How it appeared (or was constructed) would be the ...
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### MOSFET operation

I have 2 questions about the the MOSFET operation. When we apply voltage at the gate is the depletion region between the drain and the p type semiconductor destroyed? If we put a resistor to the ...
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### Normal force at junction [on hold]

Question is to compare normal forces at A,B and C. I found out theta subtended by arc AB to be $30°$. Problem is at point B. As for a point just before B, normal force is $mg\cos30° + mv^2/100$. But ...
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### What is Work Done against the Atmosphere

{Assume it's a Spherical Balloon} The answer on the book states (7pV), but I'm definitely missing something. I've looked up online on what 'Workdone against atmosphere' means but there is little to ...
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### What is self narrowing atomic beam pantography?

Can anyone please explain what is this technique. This is a topic in second unit of GTU syllabus for Nanotechnology. I googled a lot but I don't understand what is that.
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### Gravity and propulsion [on hold]

If a body (m) weighs 200 lbs (90.7185 kg) at sea level and gravity diminishes as the distance between it and the earth (M) increases, what would the body's relative weight be at an altitude of 128,000 ...
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### Rayleigh-Schrödinger series and pertubation theory

If we look at the time-independent perturbation theory and the non degenerate case where $H=H_0+\lambda H_1$ and $H_0$ has eigenvalues $E_i^{(0)}$ and normalized eigenfunctions $|\Psi_i^{(0)}>$. ...