Electrostatic Potential and Capacitance - Online Test
Q1. when two capacitors are put in series, the equivalent capacitance is
Answer : Option C
Explaination / Solution:
When two capacitors C1 and C2 are connected in series, the reciprocal of the equivalent capacitance in series is equal to the sum of the reciprocals of the two individual capacitances.
It has value lesser than the least value of capacitance.
It has value lesser than the least value of capacitance.
Q2. For a parallel plate capacitor ______________ possible potential difference between the capacitor plates
Answer : Option B
Explaination / Solution:
When a dielectric is introduced between two charged plates of a capacitor having a charge Q and maintained at a potential difference of V, a reverse electric field is set up inside the dielectric due to dielectric polarization.
This reduces the electric field in between the plates. The potential is also reduced. Maximum potential is dependent on the charge on the plates. As the charge remains constant, the presence of the dielectric decreases the maximum potential between the plates.
This reduces the electric field in between the plates. The potential is also reduced. Maximum potential is dependent on the charge on the plates. As the charge remains constant, the presence of the dielectric decreases the maximum potential between the plates.
Q3. For a parallel plate capacitor and a dielectric of dielectric constant K When a dielectric material is inserted between the plates while_______________ the potential difference between the plates decreases by a factor K
Answer : Option B
Explaination / Solution:
When a dielectric material is introduced in between the plates of a charged capacitor, which is disconnected from the battery, the charge remains constant, while the potential decreases by a factor K. The charge on the plates will increase if the dielectric material is slipped in between the plates of a capacitor which remain connected to the battery. In this case, the potential across the plates of the capacitor remains constant being equal to thebattery voltage.
Q4. The dielectric constant K of an insulator can be
Answer : Option D
Explaination / Solution:
Dielectric constant of air is 1. All dielectrics generally have a value of the dielectric constant greater than 1.where is the force between two charged particles in a medium of dielectric constant K and F is the force between the two charges when placed in air.The force between two charges is greatest in air or vacuum and it decreases when any medium is placed between the charges. K cannot have negative, fractional or zero values.
Q5. The dielectric constant K of an insulator cannot be
Answer : Option A
Explaination / Solution:
Dielectric constant of a metal is infinity, and this is why the electric field inside a metal is zero. All other substances have a dielectric constant with values less than infinity but greater than 1.
Q6. If the dielectric constant and dielectric strength be denoted by K and X respectively, then a material suitable for use as a dielectric in a capacitor must have
Answer : Option D
Explaination / Solution:
The capacitance of a capacitor increases with increase in the value of dielectric constant. =K C. Dielectric strength is the maximum electric field the material can withstand without breaking down. A high value of X and a high value of K is preferable for use in capacitors.
Q7. If one penetrates a uniformly charged metallic sphere, the electric field strength E
Answer : Option A
Explaination / Solution:
Electric field due to a solid sphere of uniform charge density at points inside the sphere varies asIt decreases at the rate However if the sphere were a hollow shell, the electric field would be zero at all points where r < R
Q8. A parallel plate condenser is immersed in an oil of dielectric constant 2. The field between the plates is
Answer : Option C
Explaination / Solution:
In the presence of a dielectric with K=2, the electric field =E/K= E/2, The force also reduces by 1/2
Q9. The capacity of a pure capacitor is 1 farad. In DC circuit its effective resistance will be
Answer : Option D
Explaination / Solution:
Capacitor does not allow DC to pass through it. The effective capacitance or the capacitive reactance , where ω is the frequency of voltage source. Since DC current is a constant current, its frequency is zero. The capacitive reactance is therefore infinity.
Q10. A metal plate of thickness half the separation between the capacitor plates of capacitance C, is inserted between the plates. The new capacitance is
Answer : Option D
Explaination / Solution:
The capacitance C of a parallel plate capacitor is given by A metal plate of thickness d/2 when introduced between the plates reduces the distance between the plates to d/2. The effective capacitance becomes
Another explanation: The system can be considered to be three capacitors , , and connected in series.
K of a metal is infinity. . The equivalent capacitance
Another explanation: The system can be considered to be three capacitors , , and connected in series.
K of a metal is infinity. . The equivalent capacitance
