Physics Multiple Choice Questions on “Dielectrics and Polarisation”.
1. In which type of molecule positive and negative charges coincide with each other?
a) Polar
b) Unipolar
c) Non-polar
d) Bipolar
Answer: c
Clarification: A molecule in which the centre of mass of positive and negative charges collide with each other is called a non-polar molecule. They normally have zero dipole moment. They have symmetrical shapes.
2. What is the ratio of the polarization to εo times the electric field called?
a) Polarisation density
b) Electric susceptibility
c) Dielectric strength
d) Dielectric susceptibility
Answer: b
Clarification: The ratio of the polarization to εo times the electric field is called the electric susceptibility of the dielectric. It describes the electrical behaviour of a dielectric.
3. Which of the following is an example of a molecule whose centre of mass of positive and negative charges coincide each other?
a) CO2
b) CO
c) CH3OH
d) NH3
Answer: a
Clarification: CO2 is a molecule in which the centre of mass of positive and negative charges collide with each other and is called a non-polar molecule. They normally have zero dipole moment. They have symmetrical shapes.
4. What is the induced dipole moment developed per unit volume of a dielectric when placed in an external electric field called?
a) Relative permittivity
b) Polarisation susceptibility
c) Electric susceptibility
d) Polarisation density
Answer: d
Clarification: The induced dipole moment developed per unit volume of a dielectric when placed in an external electric field is called polarization density. It may be defined as the charge induced per unit surface area.
5. In which type of molecule positive and negative charges does not coincide with each other?
a) Isentropic
b) Equipotential
c) Polar
d) Non-polar
Answer: c
Clarification: A molecule in which the centre of mass of positive and negative charges does not collide with each other is called a polar molecule. They have a permanent dipole moment. They have unsymmetrical shapes.
6. The molecules of a polar dielectric have no dipole moment. State true or false.
a) True
b) False
Answer: b
Clarification: The molecules of a polar dielectric have permanent dipole moments. In the absence of an external electric field, the dipole moments of different molecules are randomly oriented due to thermal agitation in the material.
7. ‘X’ is a substance which does not allow the flow of charges through it but permits them to exert electrostatic forces on one another through it. Identify X.
a) Polar molecule
b) Dielectric
c) Non-polar molecule
d) Equipotential
Answer: b
Clarification: A dielectric is a substance which does not allow the flow of charges through it but permits them to exert electrostatic forces on one another through it. A dielectric is essentially an insulator which can be polarized through small localized displacements of its charges.
8. Which of the following is an example of a molecule whose centre of mass of positive and negative charges does not coincide each other?
a) NH3
b) H2
c) CH4
d) CO2
Answer: a
Clarification: NH3 is a molecule in which the centre of mass of positive and negative charges does not collide with each other and is called a polar molecule. They have a permanent dipole moment. They have unsymmetrical shapes.