Tag: dielectric substances and polarization

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Questions Related to dielectric substances and polarization

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

The ratio of the forces between two small spheres with constant charges, in air and in a medium of dielectric constant $K$, is

  1. $1:K$
  2. $K:1$
  3. $1:K^{2}$
  4. $:k{2}:1$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The electrostatic force between charges in a medium is inversely proportional to the dielectric constant K of the medium. The ratio of the force in air to the force in the medium is therefore K:1.

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

Two conducting spheres of radii $r _1$ and $r _2$ are charged to the same surface charge density. The ratio of electric fields near their surface is -

  1. $\dfrac { { r } _{ 1 }^{ 2 } }{ { r } _{ 2 }^{ 2 } } $
  2. $\dfrac { { r } _{ 2 }^{ 2 } }{ { r } _{ 1 }^{ 2 } } $
  3. $\dfrac{r _1}{r _2}$
  4. $1:1$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The electric field near the surface of a charged conducting sphere is given by E = sigma / epsilon_0, where sigma is the surface charge density. Since the spheres are charged to the same surface charge density, the electric fields near their surfaces are equal, yielding a ratio of 1:1.

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

Two identical balls each having mass density $ \rho $ mass m and charge q are suspended from a common point by two insulating mass less string of equal length .At equilibrium each string makes an angle $ \theta $ with the vertical Now both the balls are immersed in a liquid.At equilibrium $ \theta $ remains same If the mass density of liquid is $ \sigma $ then dielectric constant of liquid will be

  1. $ \dfrac {\sigma}{\rho-\sigma} $
  2. $ \dfrac {\rho}{\rho-\sigma} $
  3. $ \dfrac {\sigma}{\rho} $
  4. $ \dfrac {\rho}{sigma} $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using the equilibrium condition for suspended charges in a medium: K = rho / (rho - sigma).

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

Force $'F'$ exists between two point charges in air, if a medium having $\epsilon _{R} = 6$ is inserted between charges, the new force between them.

  1. Will increase by $6$ times
  2. Will decrease by $6$ times
  3. Will decrease by $\sqrt {6}$ times
  4. Will increase by $36$ times
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The force in a medium is F_medium = F_air / K. With K=6, the force decreases by 6 times.

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

Two identical balls each having mass density $ \rho _1 $ mass m and charge q are suspended from a common point by two insulating massless strings of angle $\theta$ with the vertical. Now both the ball are immersed in a liquid.At equilibrium, $ \theta $ remain same. If the mass density of liquid is $ \sigma  $ then dielectric constant of liquid will be

  1. $ \frac {\sigma }{\rho - \sigma } $
  2. $ \frac {\rho }{\rho - \sigma } $
  3. $ \frac {\sigma }{\rho } $
  4. $ \frac {\rho }{ \sigma } $
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice dielectric substances and polarization dielectrics and polarisation electrostatic potential and capacitance electrostatics physics

Two charges when kept at a distance of $1 m$ apart in vacuum have some force of repulsion. If the force of repulsion between these two charges be same, when placed in an oil of dielectric constant $4$, the distance of separation is 

  1. $0.25m$
  2. $0.4m$
  3. $0.5m$
  4. $0.6m$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The electrostatic force between two charges in a medium of dielectric constant K is given by F = (1 / (4 * pi * epsilon_0 * K)) * (q1 * q2 / r^2). For the force to remain the same when placed in an oil of dielectric constant 4, the effective distance r' must be r / sqrt(K). Since r = 1 m and K = 4, r' = 1 / sqrt(4) = 0.5 m.

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

The induced charge on the dielectric of a capacitor of capacitance $4\mu F$ when charged by a battery of $50$V, is (dielectric constant of the dielectric $=4$):

  1. $100\mu C$
  2. $200\mu C$
  3. $50\mu C$
  4. $150\mu C$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Induced charge Q_i = Q_free * (1 - 1/K). Q_free = C_air * V = 4uF * 50V = 200uC. Q_i = 200 * (1 - 1/4) = 200 * 0.75 = 150uC.

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

When a metal plate is introduced between the two plates of a charged capacitor and insulated from them, then

  1. the metal plate divides the capacitor into two capacitors connected in parallel to each other

  2. the metal plate divides the capacitor into two capacitors connected in series with each other

  3. the metal plate is equivalent to a dielectric of zero dielectric constant

  4. the metal plate is equivalent to a dielectric of infinite dielectric constant
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Explanation

The capacitor is divided into two capacitors joined in series. So (b) is correct. Also as K for a metal is $\infty$, therefore (d) is also correct.

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

A charge is placed at some distance from a non uniform conductor . Now charge is slowly moved towards the conductor at a slow rate ,now which of the following is correct regarding it,

  1. surface charge density increases

  2. surface charge density decreases

  3. more charge is accumulated inside the conductor because of higher electric field.

  4. force is required to maintain the constant rate of movement of charge towards the conductor.
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

On the application of electric field on a dielectric and a conductor one by one which of the following is observed

  1. electric field inside the conductor is more as compared to dielectric.

  2. electric charge on the surface of conductor is more as compared to dielectric.

  3. electric potential energy entrapped in dielectric is more as compared to conductor .

  4. dielectric breakdown (if produced ) may allow the dielectric to function as a conductor with respect to flow of current.
Reveal answer Fill a bubble to check yourself
B,D Correct answer