Bbd Northern India Institute of Technology 2012-2013

BBD NORTHERN INDIA INSTITUTE OF TECHNOLOGY 2012-2013

UNIT-2

ASSIGNMENTS

Q1). Give the relationship between E, D, and P vectors. What is significance of each of these factors?

Q2). What is the local field? Obtain an expression for Lorentz equation for local field and hence deduce Classius-Mossotte equation.

Q3). What is the molecular polarizability? Explain different types of polarizabilities.

Q4). What is meant by local field in dielectric and how it is calculated for cubic structure?

Q5). In what way do ferroelectric materials differ from ordinary dielectric materials.

Q6). What is dielectric loss? Show that the dielectric loss is given by the relation

tan?=ℰr”/ℰr’.

Q7). Derive an expression for an energy absorbed in dielectric material when it is subjected to an alternating electric field.

Q8). Define permeability and magnetic susceptibility. Show that μ=μ0(1+χm) and

B= μ0(H+M).

Q9). Explain diamagnetism, par magnetism, and ferromagnetism on the basis of magnetic dipoles of atoms.

Q10). Describe Langevin’s theory of diamagnetism. Show that the magnetic susceptibility is negative and independent on temperature.

Q11). Show that the paramagnetic susceptibility is positive and is temperature dependent.

Q12). Explain piezo-electric effect and describe the construction and working of a piezo-electric generator for production of ultrasonic waves.

Q13). What is the phenomenon of magnetostriction? How will you produce with its help high frequency ultrasonic waves?

Q14). Describe in brief the scientific applications of ultrasonic waves.

Q15). How ultrasonic waves are detected?

Q16). The dielectric constant of helium at 0˚ C and 1 atmospheric pressure is

1.000074. Calculate the displacement induced in each helium atom when the gas is in an electric field of 1V/m. Given that ℰ0=8.85x10-12 c2/Nm2 and molecular density of helium is 2.69x1025 mole/m3 at NTP.

Q17). The dielectric constant of neon gas at NTP is 1.000134. Calculate the dipole moment induced in each atom the gas when it is placed in an electric field intensity 90,000V/m. Also find the atomic polarizability of neon. (Avogadro no 6.023 x1026 atoms/kg mole )

Q18). A paramagnetic salt contains 1028 ions/m3 with the magnetic moment of 1 Bohr Magneton (9.28x10-24 amp-m2). Calculate the paramagnetic susceptibility and the magnetization is produced in a uniform magnetic field of 0.1 tesla when the temperature is 27˚ C. Given Boltzmann constant k = 1.38x10-23 jule K-1.

Q19). A quartz crystal of thickness of 0.001 m is vibrating at resonance. Calculate the fundamental frequency. Given Y for quartz = 7.0x1010 N/m2 and ρ for quartz =2650 kg/m3 .

Q20). SONAR sends ultrasonic waves of frequency 100 kHz towards an underwater submarine. The echo is received after 3 sec. What is the depth of the submarine under water? Speed of sound in water is 1400 m/s.