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# Raj

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I am a physics student who has got interest in PC and electronics

• ### hi need help in find the max and min with a constraint of a function. thanks?

z^2 = 4(x^2 + y^2) when z>0

1 AnswerMathematics8 years ago
• ### 2 x 2 matrix question, need help. thanks?

matrix A =[5 2] matrix B=[1 2] matrix C= [6 2]

[2 1] [-2 -5] [4 1]

hence find the matrix X such that CX + B =A

2 AnswersMathematics8 years ago
• ### Need help on perticle moves under the action of gravity on a conical surface, please!!! thanks?

this is my calculation so far and have not a clue where to go from here. how to find extremal value which is max and min of z along the trajectory. maths have not been my strongest skill. thank you

https://www.dropbox.com/s/0qq6cyopw4d0bvj/photo.JP...

A particle moves under the action of gravity on a conical surface z^2 = 4(x^2+ y^2),

z ≥ 0, where z is the vertical axis. For initial position r = (1, 0, 2) and initial velocity

ṙ = (0, 2, 0) find the extremal values of z along the trajectory. Take g = 10.

1 AnswerPhysics8 years ago
• ### need help in mechanics questions please.?

A spring over a horizontal plane (no gravity) has an end tied at the fixed point O,

and a mass m attached to the other end P which moves according to Hook's law

F = (-ʎ) O ⃗ P, ʎ > 0, where the natural length of the spring is neglected. Use an inertial

(rest) reference system with origin at O and two orthonormal vectors (î, ĵ).

1. Show that the vectorial second Newton's law in this 2D problem splits into two

independent second order differential equations, and find the general solution for

each one of them.

2. Find the particular trajectory r(t) = (x(t), y(t)) fulfilling the initial conditions:

at t = 0 P is at (0, 2) with initial velocity (-1, 0).

3. By eliminating the variable t from the trajectory, find an equation F(x, y) = 0

for the geometric path of the trajectory.

2 AnswersMathematics8 years ago
• ### Mechanics question, will appreciate help.?

Hi, I am finding it a bit hard to understand with new notations with mechanics; it shouldn't be a rocket science but my lecturer is using new notations which is confusing. I would appreciate help on this question, also advise understanding questions like these will help. thanks

A particle of mass m is dropped (without initial speed) at t = 0 from a height h > 0

above sea level. The unique acting force in this initial trajectory is gravity, with

modulus mg, if we neglect the air resistance. Once submerged, two new forces appear:

(i) viscous resistance with modulus ʎ |Ż| and (ii) buoyancy force with modulus mwg,

where mw is the mass of displaced water. Choose the origin of vertical coordinate z at sea level, axis oriented upwards, and write all forces with appropriate sign.

1. Find the trajectory Z(t) of the particle from Z = h to Z = 0, and both the time

T of arrival to the sea level and the final velocity v0 = Ż (T) < 0.

2. Obtain the new dynamical equation, with all forces, when the particle sinks.

Reset time to 0, and with initial conditions Z(0) = 0 and Ż (0) = v0 find the trajectory Z(t) under the sea level along a time interval [0, T2] such that Z(t) ≤ 0

for t ∈ 2 [0,T2].

3. Discuss the sign of the acceleration in terms of the parameters (m, mw, h, g, ʎ)

4. What is the terminal velocity, for t → ∞, when m > mw? And when m < mw?

1 AnswerPhysics8 years ago
• ### Hi need urgent help in electricity and magnetism! Please..?

Do I use Bio stavart rule for this?

A transmission line (see the diagram below) consists of two parallel air spaced thin

conducting strips of negligible resistance, width w and separation d (w ª d). The

potential difference between the strips is V and they each carry the same current I in

opposite directions.

Obtain expressions, in terms of the parameters given, for:

(i) the electric field in the space between the conductors.

(ii) the magnetic field in the space between the conductors.

(iii) the capacitance per unit length of the line.

Specify the directions of the fields.

[Note that, since C is a geometrical property of the arrangement of conductors, V and

I will not appear in expression (iii)]

1 AnswerPhysics9 years ago
• ### Need urgent help in electiricity and magnetism!?

Hi I am stuck in this question, and really appreciate any help but I want to understand the concept so if you can help me to elaborate and point me in the right direction it will be great, thanks in advance..

3) (a) Obtain an expression for the capacitance per unit area of a parallel plate

capacitor, of plate separation d, when a slab of material of width w (<d) and

dielectric constant e is placed against one of the plates. (In fact, the result

does not depend on where the dielectric slab is located between the plates.)

(b) The slab has dielectric constant 2.3, width w = d/4 and is placed against the

positive plate The positively charged plate is at 100 V and the negative plate

at 0 V. Calculate:

(i) the voltage at the air-dielectric interface.

(ii) the ratio of the energy densities in the two regions of the

capacitor.

(iii) the charge density on the dielectric surface at the air-dielectric

interface if d = 0.6 mm.

1 AnswerPhysics9 years ago
• ### help needed in electricity and magnetism, please?? thanks?

The potential due to a point charge q is V(r) =q/4πε0r (zero at infinity). Obtain

the corresponding expression for the electric field by computing E(r) = -▽V(r).

*so do I integrate E(r)? is that the right way of getting the corrsponding expression for the electric field?

1 AnswerPhysics9 years ago
• ### need C program code for finding roots, using the newton-ralphson method of the function ax^2 + bx +c = y.?

Hi guys I am in the need of programming help here.

Question:

Write a structured program to find the roots, using the Newton-Ralphson method, of the function ax^2 + bx + c = y, where a, b and c are any numbers input by the user from the keyboard (not file) along with an initial guess value of x and a tolerance (convergence).Print out to screen the result of each iteration.

Include in the code a means of bailing out of the while loop if 50 iterations have passed without achieving the required accuracy - along with an error message to the screen "sorry, unable to find root to the required accuracy".

1 AnswerProgramming & Design9 years ago
• ### hey guys urgent help needed in electricity and magnetism!! Please!?

Two flat, parallel, closely spaced metal plates of area 0.08m^2 carry total charges

of -2.1µC and +3.8µC. Find the surface charge densities on the inner and outer

surfaces of each plate. Assume that the external electric fields have equal

magnitudes to the left and right sides of the plates.

2 AnswersPhysics9 years ago
• ### how much weight you will loose in a week if you do High intensity training?

How much weight will you loose in a week if you go on juice master programme 7lbs in 7days also rope in couple of High intensity training 3 times a week such as these following workout, especially the bike training

http://www.youtube.com/watch?v=00nNpZmEjXI

http://www.youtube.com/watch?v=fch3HkQgSqM

&feature=player_embedded#t=0s

thanks guys

3 AnswersDiet & Fitness9 years ago
• ### Hi I am really stuck in expectation value question in quantum mechanics. please need urgent help?

This question concerns probabilities and expectation values of a particle.

a) Write down an expression for the probability of a particle being in a certain point in

space, in terms of its wavefunction.

b) For the groundstate normalised eigenfunction in the infinite potential well problem:

What is the probability of the particle being found between 0.349a and 0.351a? (Hint:

this is a very small interval, so the function does not change much over it.)

c) By writing down an expression for the probability and value of a result – for example,

the throw of a die – explain what is meant by expectation value. By writing an

expression for the probability of a wavefunction, give the corresponding expression for

the expectation value of any observable quantity, e.g. position, x or energy, E. In

quantum mechanics, what is the operator, H? Using H, write down an expression for

<E>.

d) A wavefunction can be written as the superposition of a set of orthogonal energy

eigenstates:

Ψ(x) = Σcn Ψn(x)

What does orthogonal mean? It is often said that a wavefunction is analogous to a

Cartesian vector. How many dimensions may this quantum mechanical “function space”

have? Comment on the meaning of the Cn values.

e) A system has a complete set of eigenfunctions, ψ1, ψ2, ψ3, with energies 0.067eV,

0.23eV and 0.464eV respectively. This system is described by the total wavefunction:

ψ = 0.2 ψ1 + 0.45 ψ2 + 0.87 ψ3

Determine the expectation value of the system’s energy.

1 AnswerPhysics10 years ago
• ### Frames of reference question help please, urgent in quantum mechanics!!!?

In a collider ring, a positron and electron are both accelerated to 0.85c, though

travelling in opposite directions. Express the total energy of the positron and electron in

MeV in the lab frame of reference. Finally, determine the total momentum of the

electron and positron in the lab’s frame of reference. (Recall that a positron has the same

mass as an electron, but exactly opposite charge.)

2 AnswersPhysics10 years ago
• ### Hi I am really stuck in expectation value question in quantum mechanics, any help is appreciated, thanks!?

This question concerns probabilities and expectation values of a particle.

a) Write down an expression for the probability of a particle being in a certain point in

space, in terms of its wavefunction.

b) For the groundstate normalised eigenfunction in the infinite potential well problem:

What is the probability of the particle being found between 0.349a and 0.351a? (Hint:

this is a very small interval, so the function does not change much over it.)

c) By writing down an expression for the probability and value of a result – for example,

the throw of a die – explain what is meant by expectation value. By writing an

expression for the probability of a wavefunction, give the corresponding expression for

the expectation value of any observable quantity, e.g. position, x or energy, E. In

quantum mechanics, what is the operator, H? Using H, write down an expression for

<E>.

d) A wavefunction can be written as the superposition of a set of orthogonal energy

eigenstates:

Ψ(x) = Σcn Ψn(x)

What does orthogonal mean? It is often said that a wavefunction is analogous to a

Cartesian vector. How many dimensions may this quantum mechanical “function space”

have? Comment on the meaning of the Cn values.

e) A system has a complete set of eigenfunctions, ψ1, ψ2, ψ3, with energies 0.067eV,

0.23eV and 0.464eV respectively. This system is described by the total wavefunction:

ψ = 0.2 ψ1 + 0.45 ψ2 + 0.87 ψ3

Determine the expectation value of the system’s energy.

1 AnswerPhysics10 years ago
• ### Hi need help with energy, momentum and Compton effect, quantum mechanics? please?

What was so surprising about the Compton effect in terms of the classical theory of how electromagnetic waves are scattered by atoms? (Hint: think about the wavelengths of the incident and scattered radiation).

(ii) Using the relationship between energy E, mass m and momentum p of a particle, namely, E^2 = m^2 + c^4 + p^2 c^2 , together with E = hf, where h is a constant and f the frequency of light, derive an expression for the momentum of a photon in terms of the wavelength λ.

(iii) Draw a schematic diagram of a Compton collision. Defining the appropriate variables, write down the equations for the conservation of momentum in directions parallel and perpendicular to the direction of the incident photon.

2 AnswersPhysics10 years ago
• ### Relativity question help in quantum mechanics, pleasee!!?

Two spaceships are heading towards each other, with velocities of 0.64c and -0.64 c.

Begin by sketching this scenario, clearly indicating which frames of reference you are

using for your primed and un-primed inertial reference frames. What is the velocity of

one ship when measured from the other using Gallilean (classical) relativity? State why

this result is impossible. Use the appropriate relativistic formula to calculate the actual

relative velocity.

2 AnswersPhysics10 years ago
• ### Hi need help with infinite square well, quantum mechanics question!?

What does "normalization" mean? Given the normalized wavefunction Ψ(x) = √(2/a)sin(πx/a) for a particle in the ground state of an infinite potential well of width a, find the probability of the particle being in the first quarter of the well (0≤x≤0.25a).

1 AnswerPhysics10 years ago
• ### Hi need help in explaining Photoelectic effect and compton effect, please?

a) Describe the photoelectric effect experiment and sketch the apparatus. What four

observations led Einstein to conclude that the energy in light is contained in particle-like

quanta called photons? Write down an expression for the maximum kinetic energy

against the frequency of the light and sketch a graph of this relationship. Contrast these

observations with the expectations of classical theory. Finally, explain why no electrons

are emitted if the light has a frequency that is too low - no matter how intense the light.

b) If a piece of metal has a work function of 3.00 eV, what will the maximum kinetic

energy of electrons emitted be when the metal is irradiated by light of wavelength 321

nm? Calculate the cut off frequency below which no electrons will be emitted.

c) The particle-like nature of light also leads to the Compton effect, which considers the

scattering of electrons by photons. Explain:

i) how it is that photons can have momentum, deriving an expression for that

momentum,

ii) why the change in wavelength of photon after the scatter event is at odds with

classical theory, and

iii) write down the conservation of energy equation for the scattering event.

3 AnswersPhysics10 years ago
• ### Need help in Bohr’s Formula for Emitted Radiation question, quantum mechanics?..please?

With reference to the de Broglie's hypothesis (that the wavelength of a particle is

given by λ = h/mv where m is the mass and v the velocity) explain why in the Bohr

model of the atom only certain discrete angular momentum values are permitted. Also,

explain why physicists had believed prior to this that "orbiting" electrons were not

possible. The Balmer series is a range of frequencies f emitted from a hydrogen atom

given by:

f = K(1/4 - 1/n^2)

where n is an integer and K is a constant. For this series, down to what energy level are

the electrons dropping?

1 AnswerPhysics10 years ago
• ### Hi need help in quantum mechanics, deriving normalisation constant??..Please?

What does the term “normalisation” mean? The eigenfunctions of an infinitely deep

potential well of width a are given by the expression:

Ψn = Asin (nπx/a)

Derive the value of the normalisation constant, A. (You might find the relationship

sin2(θ) = ½ (1 – cos 2θ) useful.)

1 AnswerPhysics10 years ago