# Question Bank Solutions for BE Mechanical Engineering Semester 1 (FE First Year) - University of Mumbai - Applied Physics 1

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Applied Physics 1
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Define the critical temperature. Slow that in the superconducting state the material is perfectly diamagnetic.

 Superconductivity
Chapter:  Superconductivity
Concept: Meissner Effect

“Superconductor is a perfect diamagnetic”, Explain.

 Superconductivity
Chapter:  Superconductivity
Concept: Meissner Effect

What is reverberation time? How it is important ? write the factors affecting reverberation time.

 Acoustics
Chapter:  Acoustics
Concept: Reflection of Sound(Reverberation and Echo)

A quartz crystal of thickness 1.5 mm vibrating with resonance. Calculate it’s fundamental frequency if the Young’s modulus of quartz crystal is 7.9×1010N/m2 and density is 2650 kg/m3

 Crystal Structure
Chapter:  Crystal Structure
Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

With neat diagram of unit cell, explain the structure of NaCl crystal and calculate the no .of ions per unit cell, co ordination no. and lattice constant. Calculate the packing factor of NaCl crystal assuming the radius of Na+is 0.98 A° and radius of Cl is 1.81 A°.

 Crystal Structure
Chapter:  Crystal Structure
Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

A hall of dimension 25×18×12m3 has an average absorption coefficient 0.2. find the reverberation time. If a curtain cloth of area 150m2 is suspended at the  centre of Hall with coefficient of absorption 0.75, What will be the reverberation
time?

 Acoustics
Chapter:  Acoustics
Concept: Reflection of Sound(Reverberation and Echo)

Define ligancy and critical radius ratio. Calculate critical radius ratio for ligancy 8.

 Crystal Structure
Chapter:  Crystal Structure
Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

With neat diagram of unit cell , explain the structure of HCP crystal and calculate the no. of ions per unit cell, co ordination no., lattice constant and packing factor of the structure.

 Crystal Structure
Chapter:  Crystal Structure
Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

 Crystal Structure
Chapter:  Crystal Structure
Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

Explain with Diagram Hcp Unit Cell Based on Lattice Parameters.

 Crystal Structure
Chapter:  Crystal Structure
Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

Explain Meissner Effect with the help of diagram.

 Superconductivity
Chapter:  Superconductivity
Concept: Meissner Effect

A conference room has a total volume of 2000 m3.The magnitude of total
absorption with in the conference room is100 Sabin.Calculate thereverberation time.

 Acoustics
Chapter:  Acoustics
Concept: Reflection of Sound(Reverberation and Echo)

A quartz crystal of thickness 1 mm is vibrating at resonance. Calculate its fundamental frequency. (Assume that for quartz, Y= 7.9x 1010 N/m2 and p = 2.650 gm/cc.

 Crystal Structure
Chapter:  Crystal Structure
Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

Define Ligancy. Find the value of critical radius ratio for Ligancy 3.

 Crystal Structure
Chapter:  Crystal Structure
Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

Define super conductivity and critical temperature. Plot the variation of resistance versus temperature in case of superconducting state of the material.

 Semiconductor Physics
Chapter:  Semiconductor Physics
Concept: Conductivity, mobility, current density (drift & diffusion) in semiconductors(n type and p type)

Calculate conductivity of a germanium sample if a donar impurity atoms are added to the extent to one part in 10 germanium atoms at room temperature.
Assume that only one electron of each atom takes part in conduction process.

Given:- Avogadro’s number = 6.023 × 1023 atom/gm-mol .
Atomic weight of Ge = 72.6

Mobility of electrons = 3800 (cm^2) / ( "volts")  sec

Density of Ge = 5.32 gm/ cm3

 Superconductivity
Chapter:  Superconductivity
Concept: Type I superconductors

Describe with the necessary theory the davisson and german establishing wave nature of electrons. Calculate the de-broglie wavelength of an alpha particle accelerating through a potential difference of 200 volts given :- mass of alpha
particle = 6.68×10-27kg.

 Quantum Mechanics
Chapter:  Quantum Mechanics
Concept: De Broglie Wavelength

Define the term drift current and mobility of a charge carriers. Calculate the current product in a germanium sample of area of cross section 1 cm2 and thickness of 0.01 m, when a potential difference of 2V is applied cross it. Given :- the concentration of free electron in germanium is 2×1019 /m and mobilities of electrons and holes are 0.36 m2 /volts sec and 0.17 m2 /volts sec respectively.

 Semiconductor Physics
Chapter:  Semiconductor Physics
Concept: Conductivity, mobility, current density (drift & diffusion) in semiconductors(n type and p type)

What do you mean by group and phase velocity? Show that the de-Broglie group velocity associated with the wave packet is equal to the velocity of the particle.

 Quantum Mechanics
Chapter:  Quantum Mechanics
Concept: De Broglie Wavelength

The mobility of holes is 0.025m2 /V-sec. what would be the resistivity of n- type Si if the Hall coefficient of the sample is 2.25× 10-5m3/C.

 Semiconductor Physics
Chapter:  Semiconductor Physics
Concept: Conductivity, mobility, current density (drift & diffusion) in semiconductors(n type and p type)
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