Electrostatic Potential and Capacitance - Online Test
Q1. The amount of energy a capacitor can store is called its
Answer : Option B
Explaination / Solution:
Energy stored in a capacitor
Q2. A variable capacitor and an electroscope are connected in parallel to a battery. The reading of the electroscope would be decreased by
Answer : Option C
Explaination / Solution:
An electroscope is a device which measures the potential difference. If it is connected in parallel to the capacitor, the potential across it will be equal to the potential across the capacitor, which is equal to the potential across the battery. On decreasing the battery potential, the potential difference across the electroscope reduces and hence the reading reduces. While the capacitor is connected to the battery, Placing a dielectric between the plates, or decreasing the distance between the plates or increasing the area of the plates will not change the potential difference across it; since it will always remain equal to the potential difference maintained by the battery. In the cases B, C and D, The capacitance of the capacitor , however increases ; but this increase happens due to increase in the charge stored in the capacitor while the potential remains constant.
Q3. For a charged conductor of arbitrary shape, inside the conductor
Answer : Option C
Explaination / Solution:
The electric field on the surface of a hollow conductor is maximum and it drops to zero abruptly inside the conductor. Since, the potential difference between any two points inside the hollow conductor is zero. This means that the potential at all points inside the hollow charged conductor is same and it is equal to the value of the potential at its surface.
Q4. To make a condenser of 16 μF, 1000 volts, how many condensers are needed which have written on them “8 μF, 250 volts”?
Answer : Option D
Explaination / Solution:
Each capacitor of capacitance can withstand a maximum potential of 250 V. When equal capacitors are connected in series, the potential difference across them is equal. If there are m capacitors in series such that the potential across each is 250 V, then,. The equivalent capacitance of 4 capacitors connected in series is.To achieve a capacitance of 16 , n such rows of capacitors need to be connected in parallel. .To make a condenser of 16,8 rows of capacitors with each row containing 4 capacitors are to be connected. The total number of capacitors= n×m=4×8=32.
Q5. When 2 charged conductors are connected by a wire,
Answer : Option A
Explaination / Solution:
Let the two conductors have capacitances and and let their potentials be and . Total initial energy of the conductors. When two charged conductors are connected by a wire, the flow of charge stops when the potentials are equalized. Let V be the common potential and and be the charges on the conductors after the common potential is attained.
The final energy
The final energy
Q6. In series combination of capacitors, potential drops across the individual capacitors are equal to
Answer : Option A
Explaination / Solution:
When capacitors are connected in series, they have equal charge but the potential difference across them is given by .Therefore
Q7. An electrolytic capacitor is marked 8 μF, 220 V. It can be used in a circuit where the p.d. across the capacitor may be
Answer : Option D
Explaination / Solution:
The break down potential of the capacitor is 220 V. In order to prevent damage to a capacitor, it should be always used in a circuit where the p.d is less than its break down potential. The p.d difference can only be 200 V.
Q8. The action of the dielectric to increase the capacitance is due to
Answer : Option D
Explaination / Solution:
When a dielectric is placed between the plates of a capacitor, electric polarization results in a reverse electric field inside the dielectric.
The net electric field reduces and therefore the potential reduces. Sincethe capacitance increases because the potential reduces.The charges in a dielectric are incapable of moving since all dielectrics are essentially insulators. The molecules of the dielectric acquire an induced dipole moment in the direction of the applied field, due to rearrangement of their electron clouds.The charges in the dielectric and those on the capacitor plates are not equal in magnitude. They are not neutralized. The dipoles in the dielectric are oriented perpendicular to the plates as the electric field is perpendicular to the plates.
The net electric field reduces and therefore the potential reduces. Sincethe capacitance increases because the potential reduces.The charges in a dielectric are incapable of moving since all dielectrics are essentially insulators. The molecules of the dielectric acquire an induced dipole moment in the direction of the applied field, due to rearrangement of their electron clouds.The charges in the dielectric and those on the capacitor plates are not equal in magnitude. They are not neutralized. The dipoles in the dielectric are oriented perpendicular to the plates as the electric field is perpendicular to the plates.
Q9. In electrolytic capacitors positive terminal is
Answer : Option B
Explaination / Solution:
Aluminium electrolytic capacitors have the Aluminium foil anode (positive terminal) which is etched and covered with a layer of Aluminium Oxide which acts as a dielectric. The whole assembly is covered using a paper separator soaked in electrolyte such as, Borax or Glycol and covered by Aluminium foil which acts as cathode ( negative electrode)
Q10. Submarine cables act as
Answer : Option B
Explaination / Solution:
A submarine cable consists of an inner conductor which carries power. This conductor is covered by an insulator, which acts as a dielectric. The dielectric material is covered by a metal coating called shield, which is connected to ground.
The cable acts as a cylindrical capacitor, with the conductor acting as the inner cylinder, and the metal shield as the outer cylinder which is connected to earth.
The cable acts as a cylindrical capacitor, with the conductor acting as the inner cylinder, and the metal shield as the outer cylinder which is connected to earth.
