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Calculating the induced emf without knowing the change in magnetic flux

A conducting rod of length $\ell$ moves on two horizontal frictionless rails, as in Figure P20.30. A constant force of magnitude 1.00 N moves the bar at a uniform speed of 2.00 m/s through a ...
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0answers
14 views

Quantum Mechanics: Eigenstates for Quantum operators

1. The problem statement, all variables and given/known data Suppose that a state |Ψ> is an eigenstate of operator B, with eigenvalue bi. 2. Relevant equations i. What is the expectation value of ...
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0answers
16 views

How to compute the normal ordered angular momentum of a real scalar in terms of ladder operators?

I'm trying to compute the angular momentum $$Q_i=-2\epsilon_{ijk}\int{d^3x}\,x^kT^{0j}\tag{1}$$ where ...
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0answers
13 views

Heavy beam suspended by nylon and steel cables, angle problem [on hold]

I'm having trouble with the following simple physics problem: A heavy uniform beam of mass 8000kg and length 2,0m is suspended at one end by a nylon rope of diameter 2,5cm and at the other end by a ...
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0answers
24 views

Forces exerted on legs of a table

This is actually for a computer science homework problem, but I haven't studied any physics in five years so I'm having a bit of trouble. I'm given a table of three legs with their coordinates and I ...
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1answer
29 views

Proportionality and units

This might be very easy, but I'm not 100% sure how it's done. Lets say I have this equation: $$R = R_{0} \cdot \left[1 - \frac{P_{0}R_{0}}{GM_{0}\rho_{0}}\right]^{-1},$$ where I know $P_{0}$, ...
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2answers
174 views

Position operator in QFT

My Professor in QFT did a move which I cannot follow: Given the state $$\hat\phi|0\rangle = \int \frac{d^3p}{(2\pi)^3 2 E_p} a^\dagger_p e^{- i p_\mu x^\mu}|0\rangle,$$ he wanted to show that this ...
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0answers
14 views

Electric field due to continuous volume charge distribution [duplicate]

Since the Electric field at point (0,0,z) is $$dE = \frac{\rho vdv}{4\pi\epsilon_0R^2}\hat{R}$$ $$\hat{R} = \cos\alpha \hat{z} + \sin\alpha \hat{\rho}$$ where $\hat{R}$ means unit vector $R$. ...
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1answer
12 views

Compute convective heat transfer coefficient for a condensing steam

I have a question about convective heat transfer coefficients. I am trying to figure out how much steam I can condense in this specific heat exchanger. Steam at 9 MPa is condensed in a 1 shell pass, ...
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0answers
22 views

Circuit Diagram [on hold]

Three resistor are put into play, two in parallel and another in series to them. One of the resistors in parallel is decreased. what will happen to the voltage and current.
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0answers
26 views

Electric Field due to volume charge [on hold]

Electric Field at point P due to volume charge Since,the Electric field at point (0,0,z) is dE = ρvdvaR/4πε0R2 aR = cosα az + sinα aρ where aR means unit vector R can anyone derive the above ...
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0answers
33 views

Dry Ice Sublimation time, practical calculations [on hold]

I would like to send a parcel to a family abroad with frozen (to the temperature of -18 ° C.) products.The products are small balls having a diameter of 4 cm. Balls are made from pizza dough.Total ...
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0answers
38 views

An inclined pulley system [on hold]

M1 and M2 both are 400g. There is no friction and the pulleys are massless. I am trying to work out the acceleration on M2. I am unsure whether the acceleration should be: $a\space =Mg\space -\space ...
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1answer
55 views

The “classical radius” of the electron [on hold]

According to one theory, the mass m of the electron arises simply as a consequence of the electrostatic energy of its electric field, through Einstein's famous expression ε=mc^2, where ε is the field ...
2
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1answer
35 views

entropy of a long molecule chain with respect to its length

Consider a (very long) one-dimensional chain of $N$ moleculs, which can be in either of the energy states $\alpha$ or $\beta$. The configurations have length $a$ or $b$ respectively. Show ...
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1answer
52 views

Which moves faster in a time $t$: $A$ or $B$? [on hold]

Suppose we have two objects, $A$ and $B$, both made of the same substance. They also have the same shape (e.g. two spheres), but $A$ is larger and therefore more massive than $B$. Both $A$ and $B$ ...
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0answers
9 views

What is the power of combination of an erect and an inverted halved convex lens?

So I have this question from a competitive exam. And I don't know to solve for the second part (I have a guess at the answer, but don't quite understand it). For the first part, focal length ...
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1answer
34 views

Moment of inertia help [on hold]

Okay so lets say I have a lever with 2 objects on it, object one and object 2. Object 1 has a mass of $m_1$ and is $r_1$ away from the fulcrum; object 2 has a mass of $m_2$ and is $r_2$ away from the ...
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1answer
37 views

How to find how far away could a binary system be? [on hold]

Human eye resolution is about one arcminute. Two stars in a binary system are separated by 10 AU. How far away can they be such that your eye could still distinguish them as two separate stars rather ...
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0answers
37 views

What is the relative speed of the galaxy with respect to the Earth [on hold]

Consider a distant galaxy. Though this is a bit contrived, suppose that an astronomer measures the fourth transition of the Brackett series of transitions from n > 4 to n = 4 in Hydrogen at a ...
2
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1answer
59 views

Landau's Problem - Poisson bracks of a spherical symmetry function and angular momuntum in z axis

In landau's Mechanics, there's a problem: I think, if the function has the property spherical symmetry, or: $\phi(r,p)=\phi(-r,-p)$ The form suggested by Landau follows this property, but I can't ...
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0answers
56 views

Schrodinger Wave Functional (quantum fields) - Solving Functional Gaussian Integrals

Okay, So i'm doing some research that involves the Schrodinger representation in quantum field theory. The ground state wave functional for the Klein Gordon field is a generalized gaussian in position ...
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1answer
49 views

One step in deriving the Einstein-Hilbert action

In this amazing first principles derivation of the Einstein-Hilbert action there is one small manipulation needed to show $$c g_{ab,cd}\left(\eta^{ac}\eta^{bd} - \eta^{ab}\eta^{cd}\right)$$ is ...
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1answer
33 views

Net Electric Field of Multiple Charges [on hold]

Question: Four charges, each of magnitude +Q are placed at the corners of a square of side a. Obtain an expression for the electric potential at the centre of the square and at the mid point of one ...
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1answer
50 views

Finding the spectrum of a curious hamiltonian

I wish to analyse the following hamiltonian, i.e. find its eigenvalues and eigenstates. $$H = \frac{1}{2}\epsilon(\sigma _z \otimes \mathbb{1} + 1\otimes \sigma _z) - \Delta (\sigma _x \otimes \sigma ...
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0answers
19 views

How to calculate the atomic form factor of Lithium? [on hold]

I have a density function, $\rho=e^{\frac{-2r}{\pi a^3}}$, and I have also two numbers, but I don't know what they mean. They are: $a_k=0.2 \mathring A$ angstrom, $a_l=1.6 \mathring A$ . And teacher ...
3
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1answer
68 views

How to deal with $\nabla(\delta\Psi)$ in functional derivatives?

I am trying to compute the functional derivative of the following functional $$F[\Psi]=\int{}d^nx\Psi{}e^{(\nabla\Psi)^2}.$$ What I have tried up till now is the following ...
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0answers
25 views

Calculating time of being in a lift only by weight & travel distance

If someone is in a lift and normally weighs 90kg, when the lift starts accelerating the person weighs 100kg. After the lift has maintained a constant speed for a while it starts slowing down. While ...
0
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0answers
15 views

A car collides with a net [on hold]

A little car of 500 grams with a speed of 2 m/s collides with a net with a spring constant of 400 N/m. If the force is bigger then 40 N, the net breaks. 1) Prove that the net brakes 2) What is the ...
2
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0answers
52 views

Sum of energy for 2 solids in rotation

I would like to compute the sum of energy of the following case: Two solids are turning (disks). Yellow solid is turning at $w1 rd/s$ around its center of gravity and blue solid is turning at ...
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0answers
24 views

Accelerating disk [on hold]

A disk of radius $R$ is accelerating to the right over a plane. At $t=0$ the speed and the acceleration of the axle are $v_1$ and $a_1$ what is the velocity and the acceleration of each point (1-4 ...
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1answer
29 views

Example of a state which is positive but its partial transpose is not positive

Could any one give me an example of a state whose density matrix is positive semidefinnite but partial transpose is not positive semidefinnite?
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0answers
29 views

How to calcuate uniform circular motion? [on hold]

Given: Ideally, I maintain a speed of 265km/hr and 285 km/hr. Roughly, 73.6 m/s and 79m/s. I make a turn and experience around 4.5g's to 5.5g's, roughly 45 and 55 m/s^2, for about 7 seconds. I ...
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1answer
36 views

Catapult projectile with different mass [on hold]

We have a physics law. We made catapult and we have to launch a water balloon. However before that we have to know where the water balloon will fall. We don't have radars or stuff like that to ...
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0answers
15 views

Finding voltage drop in series parallel [on hold]

In this problem, I am asked to find the voltage drop for $R_3$. We are given that the current for one of the branches is 0.55 mA. I am somewhat familiar with Kirchoff's Law for currents and Kirchoff's ...
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1answer
44 views

How to calculate magnitute of average acceleration? [on hold]

Given: Starting from rest the acceleration is 500mph, in 1 second. How do I calculate the magnitude of acceleration for this in terms of $g$ as 9.8m/s^2? Starting off 500mph is about 220 m/s ...
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1answer
35 views

Problem with formula for parabolic motus

I know that the path made by an object thrown in air with velocity $v_0$ with an angle $\alpha$ is: $$y=x \cdot\tan \alpha - \frac {gx^2}{2v_0^2\cdot \cos^2 \alpha} $$ At school we had to use this ...
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0answers
49 views

How to describe the motion of a box initially at rest on a table rotating with an increasing angular speed? [on hold]

Consider the following diagram. A box is on a table that can move circularly and the box is connected by a string attached to the fixed bearing. At $t=0$, the box is at rest, the string of length ...
1
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0answers
29 views

Scintillator Length Calculations

This is sorta homeworkish, yet it still relates to my understanding of the physics behind it as well. Does anyone know how you determine t_98 (aka the length to contain 98% of the energy) for a ...
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0answers
11 views

Teeter Todder force of uplift [on hold]

What is the force of a 200lb man jumping from a three foot high elevation onto a four foot long teeter-todder with a four inch pivot point with a one hundred and thirty pound ma on the opposite ...
-1
votes
0answers
30 views

Here is a question I am trying to solve. Sorry for the highlighting, it is not relevant [on hold]

Thermodynamics initial pression,= 5 bar final pression= 2 bar The steam expand adiabatically PV^(1.120)=C providen initial volume= 3.64x10^(-4metres cubes) diameter piston= 50 mm= 0.05 m a) ...
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0answers
13 views

Motion in a straight Line [on hold]

A stone is projected from a height of 300m and at same time another stone is projected vertically upwards with a velocity of 100m/s Find when and where the two stones meet
0
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0answers
17 views

Calculating entropy (heat exchange) [on hold]

This is a homework question. Suppose 30 gram of metal gallium melts at 36°C. The melting temperature is 29.9 °C and specific heat of fusion is 80.3 kJ/kg. Is the total change of entropy simply ΔS = ...
2
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1answer
37 views

Calculating Boltzmann constant using semiconductor

My task from the latest laboratory exercise in physics is to calculate Boltzmann constant from known temperature, current and voltage. We were given this circuit: By changing the resistor value, I ...
3
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0answers
51 views

How do I treat the Lagrangian in the case of a rigid body?

Here's Exercise 1.11 from Goldstein's Classical Mechanics 3rd edition (the first one after having derived the Lagrangian basically): Exercise 1.11: Consider a uniform thin disk that rolls without ...
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1answer
31 views

Show the equivalence of two electrostatic energy

$$U = \frac{1}{2}\iint_{all space}^{ } \frac{\rho(1)\rho(2)}{4\pi\epsilon_{0}r_{12}}dV_{1}dV_{2} $$ and $$U = \frac{\epsilon_{0}}{2}\int_{allspace}^{ } \vec{E} \cdot \vec{E} dV.$$ In the left ...
1
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1answer
45 views

Entanglement Hamiltonian for two 1/2 spin system

Consider a two 1/2-spin state $$|\phi\rangle=\frac{1}{\sqrt{2}}(|1\rangle_A\otimes|1\rangle_B-|0\rangle_A\otimes|0\rangle_B),$$ cut in half (so we get A- and B-subsystem), the reduced density matrix ...
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0answers
14 views

Angular velocity and linear velocity [on hold]

Define and EXPLAIN average angular velocity and acceleration. Define and EXPLAIN instantaneous angular velocity. Experiment was about throwing a cricket ball. the shoulder is the point of reference. ...
0
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0answers
31 views

Charge density within radius r from the nucleus

The probability of finding an electron within radius $r_b$ for Hydrogen near the center ($r_b<< a_0$) is approximately equal to zero (according to 1s orbital curve). Does this imply that the ...
0
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0answers
21 views

Energy and momentum [on hold]

In a good wind location offers a modern wind turbine with a maximum output of 1 MW over 2 million kWh per year. a) How many m ^ 3 of oil is equivalent to that energy content if 1 liter of oil ...