# GATE (Graduate Aptitude Test in Engineering) Physics: Questions 628 - 632 of 659

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## Question 628

Appeared in Year: 2017

### Describe in Detail

Essay▾

The atomic mass and mass density of Sodium are and , respectively. The number density of valence electron is . (Up to two decimal places) (Avogadro number, )

### Explanation

The number density of valence electrons is,

Where, is the valency.

is the mass density

is the atomic mass

According to question, for sodium;

## Question 629

Appeared in Year: 2017

### Question

MCQ▾

The real space primitive lattice vectors are and . The reciprocal space unit vectors and for this lattice are, respectively;

### Choices

Choice (4)Response

a.

and

b.

and

c.

and

d.

and

## Question 630

Appeared in Year: 2017

### Describe in Detail

Essay▾

The total energy of an inert – gas crystal is given by , where is the inter – atomic spacing in Angstroms. The equilibrium separation between the atoms is ________ Angstroms. (up to two decimal places) .

### Explanation

Here, the total energy of an inert – gas crystal is given,

Where, is the inter – atomic spacing in Angstroms.

If at equilibrium, separation between atoms is , then becomes minimum. Therefore,

… (2 more words) …

## Question 631

Appeared in Year: 2017

### Describe in Detail

Essay▾

Consider a 2 – dimensional electron gas with a density of . The Fermi energy of the system is (up to two decimal places) .

### Explanation

The Fermi – energy of 2 – dimensional electron gas with a density of is given as,

… (2 more words) …

## Question 632

Appeared in Year: 2017

### Question

MCQ▾

If the Lagrangian is modified to , which one of the following is TRUE?

### Choices

Choice (4)Response

a.

The canonical momentum and equation of motion do not change

b.

Canonical momentum does not change, equation of motion changes

c.

Canonical momentum changes, equation of motion does not change

d.

The canonical momentum and equation of motion change

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