Energy of a Capacitor

Q. a body executes SHM with an amplitude A . at what displacement from the mean position is the potential energy of the body one -fourth of its total energy

Q. The energy of a $100\mu \text{F}$ capacitor charged to $6\text{kV}$ is used to lift a $50\text{kg}$ mass (by powering a motor by energy of capacitor) without incurring any losses. What would be the greatest vertical height through which mass could be raised?
(Take $g=10{\text{m/s}}^2$)

1. $1.6\text{m}$
2. $1.2\text{mm}$
3. $3.6\text{m}$
4. $0.6\text{mm}$

Q.

Find the loss of energy as heat when the key is swithed from position A to B.

1. $Zero$
2. $C{V}^2$
3. $4C{V}^2$
4. $2C{V}^2$

Q. Electric charges are distributed in a small volume. The flux of the electric field through a spherical surface of radius $10\text{cm}$ surrounding the total charge is $25{\text{N-m}}^2/\text{C}$. The flux over a concentric sphere of radius $20\text{cm}$ will be

1. $100{\text{N-m}}^2/\text{C}$
2. $25{\text{N-m}}^2/\text{C}$
3. $50{\text{N-m}}^2/\text{C}$
4. $75{\text{N-m}}^2/\text{C}$

Q. Find the charge and potential drop across the capacitor $C_4$ in the given circuit ?

1. $\frac{30}{7}\mu \text{C},\frac{15}{7}\text{V}$
2. $\frac{40}{7}\mu \text{C},\frac{20}{7}\text{V}$
3. $\frac{20}{7}\mu \text{C},\frac{40}{7}\text{V}$
4. $\frac{80}{7}\mu \text{C},\frac{40}{7}\text{V}$

Q.

Two spheres of radius 12cm and16cm have equal charge. The ratio of their energies is

1. 3:4
2. 4:3
3. 2:1
4. 1:2

Q. The energy stored in a condenser of capacity C which has been raised to a potential V is given by

1. 

2. 

3. 

4. 

Q. To calculate potential energy of a system of definite shape then we consider the centre of mass?

Q. In the given circuit after closing switch s

1. Work done by 3 V cell is $-27\mu J$
2. Energy stored in $2\mu F$ capacitor increases
3. Energy stored in $4\mu F$ capacitor increases
4. Energy stored in $2\mu F$ capacitor decreases.

Q. When we say that a capacitor with at a certain potential and charges on the plates has a certain amount of energy, what do we mean?

1. The charges on the capacitor radiate energy.
2. A capacitor with a potential difference across its plates has kinetic energy.
3. An external agent like a battery does work which is stored as the potential energy of the charges on the capacitor.
4. None of these.

Q. A part of circuit is shown in figure. Energy stored in $0.2\mu F$ capacitor in steady state in microjoules is

Q. why potential energy in negativ

Q. I have a capacitor who’s potential difference between the plates is maintained at 5V using a battery. If the capacitance is 5 F and a dielectric of relative permittivity 3 is placed between the plates such that it fully fills the space, What is the change in energy?

1. Increases by $6.24\times {10}^{-4}J$
2. Decreases by $6.24\times {10}^{-4}J$
3. Increases by $9.36\times {10}^{-4}J$
4. Decreases by $9.36\times {10}^{-4}J$

Q. If the energy stored in a condenser is increased by 300%, its potential difference increases by?

1. $900\%$
2. $1600\%$
3. $200\%$
4. $100\%$

Q. The electric current in a charging R−C circuit is given by i = i₀ e^−t/RC where i₀, R and C are constant parameters of the circuit and t is time. Find the rate of change of current at (a) t = 0, (b) t = RC, (c) t = 10 RC.

Q. If weight is 20kgwt and height it is kept is 5meters then what will the potential energy in joules?

Q. A capacitor stores energy within a dielectric between the conducting plates in the form of .

1. a magnetic field
2. positive voltage
3. an electric field

Q. If at $t=0$, switch $\text{S}$ is closed, at steady state find heat generated $\left(H\right)$ in the given circuit having a battery of $16\text{volts}$.

1. $640\mu \text{J}$
2. $320\mu \text{J}$
3. $1280\mu \text{J}$
4. $192\mu \text{J}$

Q. Figure shows two identical parallel plate capacitors connected to a battery through a switch S. Initially, the switch is closed so that the capacitors are completely charged. The switch is now opened and the free space between the plates of the capacitors is filled with a dielectric of dielectric constant 3. Find the ratio of the initial total energy stored in the capacitors to the final total energy stored.

1. 9 : 16
2. 5 : 9
3. 2 : 3
4. 3 : 5

Q. The work done in placing a charge of $8\times {10}^{-18}$ coulomb on a condenser of capacity 100 micro-Farad is:
[AIEEE-2003]

1. $16\times {10}^{-32}joule$
2. $3.1\times {10}^{-26}joule$
3. $4\times {10}^{-10}joule$
4. $32\times {10}^{-32}joule$

Q.

The capacity of a condenser is 4x10^-6 farad and its potential is100 volts. The energy released on discharging it fully will be

1. 0.02 Joule

2. 0.04 Joule

3. 0.025 Joule

4. 0.05 Joule

Q. The energy stored in a condenser of capacity C which has been raised to a potential V is given by

1. 

2. 

3. 

4. 

Q.

a pump on the ground floor of a building can pump water to fill tank of volume 30m^3 in 15 minutes.Iftank is 40m above the ground and the effifciency of pump is 30%, how much electric power is consumed by the pump?