Tag: electrostatic potential and capacitance

Quizzes (5) Questions (109)

Questions Related to electrostatic potential and capacitance

Multiple choice dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

A parallel plate condenser of capacity $10\mu F$ is connected to an A.C. supply voltage $e = 4\sin \left( {100\pi t} \right)$. The maximum displacement current:

  1. $4\pi \mu A$
  2. $4\pi mA$
  3. $2.8\pi \mu A$
  4. $2\pi \mu A$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Displacement current, ${i _d} = {\varepsilon _ \circ }A\frac{{dE}}{{dt}}$
where, $A$ is area and $E$ is electric field
$\begin{array}{l}E = \frac{e}{d} = \frac{{4\sin (100\pi t)}}{d}\{i _d} = {\varepsilon _ \circ }A \times \frac{1}{d}\left[ {\frac{d}{{dt}}\left( {4\sin 100\pi t} \right)} \right]\ = \frac{{{\varepsilon _ \circ }A}}{d}.4(cos100\pi t) \times 100\pi \ = C.400\pi .cos100\pi t\{\left( {{i _d}} \right) _{\max }} = \left( {10 \times {{10}^{ - 6}}} \right) \times 400\pi A\ = 4\pi  \times {10^{ - 3}}A = 4\pi mA\end{array}$

Multiple choice dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

Which of the following can be used as dielectric?

  1. Plastics

  2. Mica

  3. Porcelain

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The dielectric is a material through which no electric current passes. Here the given materials-plastic, mica and porcelain are all the  dielectric because current can not pass through them.

Multiple choice dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

Which of the following is/are non-polar dielectrics?

  1. $HCL$

  2. Water

  3. Benzene
  4. $NH _3$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Ammonia and $HCl$ are polar molecules since they have a net dipole moment towards a particular direction. Both water and benzene are non-polar molecules. But water is a conductor of electricity, whereas benzene is a dielectric (insulator).

Multiple choice dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

Breakdown voltage is
$A$. voltage at which dielectric behaves as conductor
$B$. voltage at which molecules starts flowing inside the dielectric freely.
Which of the following is correct regarding above case,

  1. Both $B$, $A$ are correct
  2. $B$ is correct
  3. $A$ is correct

  4. None of the above is correct
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Breakdown voltage for a dielectric is the maximum voltage at which, applied electric field becomes so high that electrons break up from the molecules of dielectric and becomes free inside the dielectric due to this dielectric becomes conductive. 

Multiple choice dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

Which of the following statement is false in context of dielectric?

  1. Materials of polar molecules have higher dielectric constant.

  2. Materials of polar molecules have lower dielectric constant.

  3. Materials of polar molecules have higher breakdown voltage.

  4. Materials of polar molecules have lower breakdown voltage.
Reveal answer Fill a bubble to check yourself
A,D Correct answer
Multiple choice dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

If $C$ is the value of the capacitance of a capacitor filled with a given dielectric and $a$ is the capacitance of an identical capacitor in a vacuum, the dielectric constant, symbolized by the Greek letter kappa, , is simply expressed as

  1. $\dfrac{C}{a}$
  2. $\dfrac{a}{C}$
  3. $C\times a$

  4. None

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The capacitance of a parallel plate capacitor filled with the given material of dielectric constant $\kappa$ is given by:

              $C=\dfrac{\kappa\varepsilon _{0}A}{d}$ .....................eq1
And the capacitance of the same capacitor without the given material is given by:
              $a=\dfrac{\varepsilon _{0}A}{d}$  .....................eq2
Dividing eq1 by eq2:
              $C/a=\kappa$

Multiple choice dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

Which of the following is polar dielectrics?

  1. $HCL$
  2. $NH _3$
  3. $H _2O$

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Polar dielectric are those in which center of positive and negative charge is not same due to their shapes. 

$HCl$ , $NH _{3}$ and $H _{2}O$ all are polar dielectrics due to their high dielectric constant formed due to the difference in the polarity.

Multiple choice dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

The insertion of a dielectric between the plates of a parallel-plate capacitor always 

  1. increases its capacitance

  2. decreases its capacitance

  3. remains same its capacitance

  4. none of the above

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The capacitance of a parallel plate capacitor completely filled with a given material of dielectric constant $K$ is given by:

              $C=\dfrac{K\varepsilon _{0}A}{d}$ .....................eq1
And the capacitance of the same capacitor without the given material is given by:
              $C'=\dfrac{\varepsilon _{0}A}{d}$  .....................eq2
Dividing eq1 by eq2:
              $C/C'=K$
As $K>1$ always, hence $C>C'$ i.e. the insertion of a dielectric between the plates of a parallel -plate capacitor always increases the capacitance.