### How to crack Physics PhD Interview

### In this post I’ll be telling you the strategy to crack Physics PhD interview.

After Cracking CSIR NET, GATE, JEST or any other PhD entrance examination the last hurdle is the interview. In this post I’m explaining you step by step the strategy to crack Physics PhD interview. The author is IIT Bombay topper.

### Truth Beauty – Beauty Truth

Never Tell lie

Answer as much as you know

If you don’t know then simply say “I don’t know”

**If you got low marks in your ****B.Sc**** / ****M.Sc**** and you are asked about reasons in the interview – Simply Say – ****“I should have studied better”****. Don’t cite your illness / discrimination by profs / blame your university**

### Answer Physically – Don’t just tell terms

Suppose you are asked **“What is Spin – Orbit coupling?”**

Will you just write Spin Orbit Hamiltonian?

Will you just tell “It is the mechanism responsible for LS coupling”

No…. ! You need to answer physically.

From the reference frame of electron proton orbit around it in a circle. A charge, moving in a circular loop creates a current. That current creates a magnetic field in the center of the loop.

Electron has its intrinsic spin magnetic moment. That mag moment interacts with the magnetic fields of revolving proton. That creates an interaction potential.

The whole situation is exactly similar from the perspective of proton also. This interaction is the SPIN – ORBIT Coupling.

**I think you got my point.**

Answer Physically as much as you can.

Assume your interviewer is just a class 12 student.

Explain from very basic.

It is the test how much physics you know. Not how many terms you know.

Never tell any term which you can’t explain.

### Prepare At least Two Topics

Don’t just prepare one Topic – Prepare at least two

Choose at least two among – Classical, Quantum, Math Methods, ED, Stat

You must have good concepts in your special paper.

You must have properly understood what you have done in your M.Sc project and the Physical Principles behind it.

### Back to the basics

Read basic texts and focus on most basic concepts – You won’t be asked advanced things – rather most basic ones.

For example – you can be asked to plot tanh(x) vs x graph. Or you can be asked to explain Maxell’s equations of Electromagnetism.

————-Read————-

Arthur Beiser’s “Concepts of Modern Physics” thoroughly.

Griffith’s Quantum Mechanics first three chapters.

Landau’s Mechanics – chapter 1 & 2 for interview

Kittel – first six chapters if you are applying in cond. matt.

### Classical Mechanics – Common Interview Questions

Why do you use Lagrangian formulation over Newtonian formulation? What are the advantages?

Discuss the advantages of Hamiltonian formulation over Lagrangian formulation.

When a transformation called Canonical ?

What are space time symmetries? What are the relation between the symmetries and conservation laws?

### Quantum Mechanics – Common Interview Questions

You had assumed one very important property when u derive time independent Schrodinger equation starting from time dependent equation. What was it?

When does the derivative of **ψ** becomes discontinuous and why?

How does an operator changes when you change the basis?

What can you conclude when you are informed that two operators commute?

State the basic properties of Lee Algebra. Which operators follows it?

What is a stationary state? If the hydrogen atom states are stationary then why the atom radiate from excited state?

What are the “approximations” in Born approximation?

### Statistical Mechanics – Common Interview Questions

Relation between entropy, disorder and time. What is Gibs paradox?

What is the difference between 1st & 2nd order phase transition?

What are the basic postulates of Thermodynamics and Stat. Mech

Discuss the basic differences between Bosons and Fermions?

What is the basic difference between Micro-canonical, Canonical, and Grand-canonical ensembles?

If one container of each Boson and Fermion gas are kept at same temperature, pressure of which gas will be higher and why?

### Mathematical Physics – Common Interview Questions

Draw plots of tanh(x), xsin(x), sin(x)/x, ln(x)/x, Bessel functions.

Physically explain gradient, divergence and curl of a vector.

Explain similarity transformation with properties and physical significance.

When do a matrix become diagonalizable?

What is the basic difference between Taylor and Laurent Series?

What is Wornskian? When do you use it?

What are ordinary and regular singular points?

What is a group? What do you mean by group representation?

What is a tensor?

### Electrodynamics – Common Interview Questions

Explain Maxwell’s equations Physically.

How will you write Maxwell’s equations if magnetic monopoles exist?

What will be electric dipole moment of two positive charges (q) separated by some distance (d)?

Why an em wave transverse? Explain with Maxwell’s eqs.

Explain the concept of retarded potential.

Explain the basic differences between Coulomb and Lorentz gauge? When should you use which gauge?

How much energy a accelerating charge *q* moving with acceleration *a* radiates?

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