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1. Charge conservation

so it is the algebraic sum of total charges, not the total charges am i right?
2. Charge conservation

A isolated system in which number of charges present is always constant. Suppose a high energy gamma radiation enters into the isolated system and produces positron and electron (pair production), now the total number of charges present in the system increases right? Then how the charge...

A person in the Earth (stationery frame) observes the clock in the spaceship (which almost moving at the speed of light) runs slow right? and an astronaut in the space-ship observes the clock in the earth, to him the clock also appears slow the same rate as the person observes the clock in the...
4. Doppler effect

A train (source) approaching a stationery observer, wavelength of the sound is equal to the distance between source and observer, How?
5. Hydrogen atom

How an electron transition from lower energy state to higher energy state in hydrogen atom emits a photon?
6. Newton's Third Law and forces

Why forces acts on two different bodies with same magnitude and opposite in direction doesn't cancel each other?
7. Thermodynamic functions

What are the purposes of defining the Thermodynamic functions such as H (enthalpy), G (Gibbs function), A (Helmholtz function) in Thermodynamics. I just know the expressions for this functions but unable to understand the physical significance of these functions and also haven't understand what...
8. Postulates of STR

The speed of light is constant in all inertial frames of reference Imagine a thought experiment, an observer at rest sending a light pulse towards a spaceship, he measures the speed of light to be 3x10^8 m/s, now assume that the spaceship also travels at the speed of light and an astronaut in...
9. Virtual displacement and D'Alembert's principle

While deriving lagrangian equation using D'Alembert's principle, in Goldstien, they defined a variable called "virtual displacement". Why do we need a concept called virtual displacement? What is its signigicance in classical physics?
10. Phase change

Consider a plane beam of light is falling normally on a material with thickness (d) and refractive index (n), the light partially transmits and partially reflects the light, so the light transmitting the light travels a distance (2nd) coming out of the material have a phase change of ∏ always...
11. Mass dependence

Homework Statement I have proved that η does not depend on l, but in the solution the author (classical mechanics by David Morin) claimed that η depends on both of the masses M and m, But i don't understand how, please explain me? Homework Equations The Attempt at a Solution
12. 1st order ODE

Homework Statement Solve the below differential equation Homework Equations The Attempt at a Solution I have attached my attempt at solution. But I don't how to get rid of (ln y) term in my equation i.e, i Don't know how to write in terms of y. Please help
13. Inertial frames

How Earth is considered to inertial frame of reference?
14. Uniqueness and existence

How to understand Uniqueness and existence theorem for first order and second order ODE's intuitively?
15. Fermat's principle Integral

I am unable understand this Integral, what does it actually saying? What does that "δ" means here? I haven't learned Calculus of variations, explain me with diagrams with possible.
16. Fermat's Principle expression

The expression gives time taken to reach a a distance ds in a medium. The expression has the dimension of time, But my question is how come the denominator is (c/n)? why it can't be (cn)? explain me.
17. Phase velocity

What is phase velocity? I know it is defined as v=ω/κ But what does this phase velocity tells about the wave? Does it means the velocity of wave?
18. Plane wave

From Optics by Hecht He says "only a plane wave of infinite extent will propagate as a plane wave" What does it mean by " plane of infinite extent" in this context?
19. Divergence homework problem help

Here's my attempt to the problem
20. Divergence homework problem help

Homework Statement How divergence of r (cap)/ |r|^2 is equal to zero? Homework Equations r(cap)= x(cap)+y(cap)+z(cap) |r|^2 as x^2+y^2+z^2 The Attempt at a Solution I tried the problem and end up with with a different solution I took r(cap)= x(cap)+y(cap)+z(cap) |r|^2...
21. Thermodynamics, Exact differentials

There exist exact differential for P (Pressure) ,V (volume) ,T (temperature), U (Internal Energy) but not for W(work), Q (heat) . Why?
22. Harmonic waves

What is the difference between propagation number(K) and wave number(k) described in Optics book written by hecht He defined K=2π/λ and k=1/λ and both of them have the same units (i.e, meter inverse) What does wave number of a Harmonic function tells about?
23. Why heat can't be expressed as exact differential function?

(1) Why differential of work, heat can't be expressed as exact differential function? (2) How differential of internal energy is an exact differential function and how it is a function of any two of thermodynamics coordinates?
24. Internal Energy

(1) Exact form of U exists because of the results of experiments in adiabatic work, what are such experiments which gives proof for above statement? (2) Is differential of Internal energy dU path dependent?
25. Prerequisites of Biophysics

I looking for grad level and i know school level biology. Is that enough for learning Biophysics?
26. Prerequisites of Biophysics

I am physics undergrad and very keen to learn Biophysics. But the problem is I don't know anything about it, I don't know where to start it. Should I need to know much Biology concepts to start learn Biophysics? If yes tell me what are some topics i should know to learn Biophysics.
27. Extensive properties

Why should we bother about Extensive properties in Thermodynamic systems? and Why do we need specific value of some thermodynamic property? and what does it tell us about the system? Eg. specific heat capacity? How density of a thermodynamic system is a intensive property?
28. Pressure energy

Homework Statement Consider a tube of uniform cross section, let one end (a) of the tube is at height h1 and other end (b) is at height h2, where h2>h. Now an incompressible fluid passing through the tube the workdone to pass the liquid at end (a) P1V1 and workdone to pass the liquid at end...
29. Charges in conductor

Homework Statement Let L be the length of the conductor having uniform cross-section area A and density, let I be the current passing through the conductor. How the total number of positive charge carriers in the conductor of length L is (nAL)?
30. Vector analysis: show the object moves on the elliptical path

Homework Statement problem form div curl grad and all that by h.m.schey An object moves in xy-plane in such a way that its position vector r is given as a some function of "t" by r= i acosωt+j bsinωt show the object moves on the elliptical path Homework Equations (x/a)^2+(y/b)^2=1 The...
31. Linear Algebra-Linear dependence

Homework Statement let U be a 3x3 matrix containng columns C1, C2, C3. The three column vectors C1= (a,0,0) , C2=(b,d,0), C3=(c,e,f) prove that if a=0 or d=0 or f=0 (3cases), the columns of U are dependent? problem from Linear algebra and applications, fourth editon, Gilbert strang...
32. Vector analysis

Homework Statement This picture is taken from Div, curl, grad and all that by schey, while finding the unit normal vector of the surface S (defined as w=f(x,y)) at a point P, to find the normal vector he considered a two tangent non-collinear vectors (u and v) at a point P, to find u...
33. Use of dirac delta function

If you ask me define Dirac delta function, i can easily define it and prove its properties using laplacian or complex analysis method. But still i don't understand what is the use of DIRAC DELTA FUNCTION in quantum mechanics. As i have done some reading Quantum mechanics from Introduction to...
34. Undergraduate level research topic in physics

I am a Final year (3rd year) student studying BSc Physics in India. My undergraduate course is getting completed in one month. As I want to pursue my career in field of physics, I like to do a project especially a theoretical project (kind of writing a junior level thesis) before joining...
35. Doubt in mass suspended by spring

Consider a mass M, suspended by a weightless spring (horizontally or vertically). If I apply a force on the mass M, it executes simple harmonic motion. My question is for small displacement (that is pushed or pulled) according to Hooke's law F=-kx, it is equal to force we applied right...
36. Doubt in electromagnetic spectrum

In electromagnetic spectrum, why there is no radiation less than wavelength of Gamma rays and waves higher than the wavelength of Radio waves?
37. Initial velocity

A stone released from balloon moving upwards with some constant velocity, the initial velocity of stone is same as the velocity of balloon with opposite sign, but how? What i thought is that the instant stone is released which goes upwards with balloon, stone which is going upwards would stop...
38. Frictional force and Normal force

when a body is slided or move in a horizontal floor, the Frictional force is directly proportional to the Normal force acting on the body. Is there is any proof (emperically or Theoretically)
39. Type of force

What kind of force is Friction, force applied on a particle? Are these are Electromagnetic in nature?
40. Stress, strain, pressure

Is that internal force is restoring force?If yes, Does that mean all internal forces are restoring forces?
41. Clarification in concept of planar motion of rigid body

When a Rigid body is said to be in planar motion, if all all the particles in the Rigid body moves in same plane and these planes are parallel to each other. I think i misunderstood this definition especially the particles moves in same plane and these planes are parallel to each other...
42. Stress, strain, pressure

I studied that Stress is defined as Force per unit area. Force here referred to internal force between the particles in the materials per unit area. am i right? Is pressure a kind of stress? (Internal force per unit volume) for fluids but i have studied that pressure is external force per...
43. The gravitational acceleration g

Suppose a particle of mass M is under gravitational attraction. The Newton's law of gravitation says that F=GMm/r^2, and the part Gm/r^2 is g (acceleration due to gravity how?)
44. Clarification in the definition of force

\According to Newton's second law, force is defined as rate of change of momentum or force is defined as product of mass into acceleration, I both of these definitions are same and right. My questions are, (1) how can i prove this two definitions are same?
45. What does interaction means?

when we say two masses or charges or particles interacts with each other, we have used the word interacts, what does that mean, does that mean a physical contact or something of that kind?
46. Doubt in Law of mutual interaction

It is a core topic in classical mechanics sir.
47. Doubt in Law of mutual interaction

Book: Classical mechanics (textbook) by Douglas Gregory (cambridge publications) Law of mutual interaction states that when two particle (let it be P1 and P2) interacts, the particle (P1) induces an instantaneous acceleration (a21) on particle P2 and the particle P2 induces an instantaneous...
48. Doubt in Inertial frame of reference

Newton's laws of motions are not applicable in Non-inertial frames of reference which means only mutually accelerated frames of references, My question is how can we apply Newton's laws of motions for practical experiments such as simple pendulum, motion of a ball, etc. conducted in near surface...