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All questions of Electrostatic Potential and Capacitance for NEET Exam

Three capacitors, each of capacitance C = 3 mF, are connected as shown in the figure. The equivalent capacitance between points P and S is
  • a)
    9 μF
  • b)
    6 μF
  • c)
    3 μF
  • d)
    1 μF
Correct answer is option 'A'. Can you explain this answer?

Dr Manju Sen answered
If P is at positive potential, then Q is at negative potential and R is at positive potential. The system therefore reduces to 3 capacitors in parallel. C= 9μF
  • a)
    0.5 J
  • b)
    1.12 J
  • c)
    1.2 J
  • d)
    0.9 J
Correct answer is 'D'. Can you explain this answer?
Nikita Singh answered
q=6x10-10 c
Q=-2x10-9c
r1=3x10-2m
r2=4x10-2m
△vQ=w/q
(1/4πεo)-2x10-9/10-2[(1/4)-(1/3)]=W/6x10-3
9x109x2x10-9x6x10-3/12x10-2=W
W=9x10-3x102
W=0.9J

The amount of work done in moving a charge from one point to another along an equipotential line or surface charge is
  • a)
    Zero
  • b)
    Infinity
  • c)
    One
  • d)
    Two
Correct answer is option 'A'. Can you explain this answer?

Om Desai answered
Since Potential difference between two points in equipotential surfaces is zero, the work done between two points in equipotential surface is also zero.

Work done in carrying 2C charge in a circular path of radius 2m around a charge of 10C is​
  • a)
    6.67J
  • b)
    60J
  • c)
    Zero
  • d)
    15J
Correct answer is option 'C'. Can you explain this answer?

Suresh Iyer answered
The overall work performed in carrying a 2coulomb charge in a circular orbit of radius 3 m around a charge of 10 coulomb is calculated below.
It is a well-known fact that W=qdv.
Here dV is the change in overall potential. In the circular orbit of r potential at each point is similar.
Most significantly, the value of r is 3.  
The value of dv=0 and hence W=q0=0.

If 100 J of work has to be done in moving an electric charge of 4C from a place where potential is -5 V to another place, where potential is V volt. The value of V is
  • a)
    15 V
  • b)
    20 V
  • c)
    25 V
  • d)
    10 V
Correct answer is option 'B'. Can you explain this answer?

Suresh Iyer answered
From the definition, the work done to a test charge ‘q0’ from one place to another place in an electric field is given by the formula
W=q0x[vfinal-vinitial ]
100=4x[v-(-5)]
v+5=25
v=20V
 

A hollow metal sphere of radius 5cm is charged so that the potential on its surface is 10V. The potential at a distance of 2cm from the centre of the sphere is
  • a)
    4V
  • b)
    zero
  • c)
    10/3V
  • d)
    10V
Correct answer is option 'D'. Can you explain this answer?

Ayush Joshi answered
In the case of a hollow metal sphere (spherical shell), the electric field inside the shell is zero. This means that the potential inside the shell is constant. Therefore the potential at the centre of the sphere is the same as that on its surface, i.e. 10 V. 

Two capacitors of 20 μƒ and 30 μƒ are connected in series to a battery of 40V. Calculate charge on each capacitor.​
  • a)
    480 C
  • b)
    478 C
  • c)
    450 C
  • d)
    500 C
Correct answer is option 'A'. Can you explain this answer?

Nikita Singh answered
C1= 20×10µf
and C2= 30×10µf
in series Ceq = C1C2/(C1+C2)
Ceq = 20×10^(-6)×30×10^(-6)/20×10^(-6)+30^×10(-6)
Ceq= 12×10^(-6)f
As we know that Q = CV
Putting the values of C and V= 40V, we get
Q = (12 * 10^-6) * 40
= 480µC

The shape of equipotential surface for an infinite line charge is:​
  • a)
    Coaxial cylindrical surfaces
  • b)
    Parallel plane surfaces
  • c)
    Parallel plane surfaces perpendicular to lines of force
  • d)
    None of above
Correct answer is option 'A'. Can you explain this answer?

Rajesh Gupta answered
The shape of equipotential surface for an infinite line charge is coaxial cylindrical because A curved surface on which potential is constant is equipotential curve . If we consider the line charge then the focus of the point should have the same potential hence it is a coaxial cylinder.

When a positive charge is moved in an electrostatic field from a point at high potential to a low potential, its kinetic energy
  • a)
    Remains constant
  • b)
    Decreases
  • c)
    Increases
  • d)
    Either increase or remain constant
Correct answer is option 'C'. Can you explain this answer?

You can generalise it by assuming a positive charge moving away from another positive charge. now both of them are repelling each other with some force. so that positive charge will accelerate which results in the increase in K.E.

Electric potential is
  • a)
    scalar and dimensionless
  • b)
    vector and dimensionless
  • c)
    scalar with dimension
  • d)
    vector with dimension
Correct answer is option 'C'. Can you explain this answer?

Pooja Mehta answered
He electric potential due to a system of point charges is equal to the sum of the point charges' individual potentials. This fact simplifies calculations significantly, since addition of potential (scalar) fields is much easier than addition of the electric (vector) fields.

Can you explain the answer of this question below:

The potential energy of a system containing only one point charge is

  • A:

    Zero

  • B:

    Infinity

  • C:

    Nonzero finite

  • D:

    None of the above

The answer is a.

.mie. answered
Answer is 0 as there are no other sources of electrostatic potential .... against which an external agent must do work.... in moving the point charge.... from infinity to its final location.... therefore correct opt is A

when two capacitors are put in series, the equivalent capacitance is 
  • a)
    the reciprocal of the capacitances
  • b)
    smaller than both capacitances
  • c)
    the sum of the capacitances
  • d)
    the product of the capacitances 
Correct answer is option 'B'. Can you explain this answer?

Explanation: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.

What is the direction of the lines of force at any point on the equipotential surface?
  • a)
    Parallel to it
  • b)
    Perpendicular to it.
  • c)
    Inclined at 45 degrees
  • d)
    None of the above
Correct answer is option 'B'. Can you explain this answer?

Anjali Iyer answered
When electric lines of force get perpendicular to equipotential surface then area vector and electric lines of force are parallel to each other.so angle between them is zero. due to that reason they get perpendicular to each other.

In bringing an electron towards another electron, the electrostatic potential energy of the system
  • a)
    becomes zero
  • b)
    decreases
  • c)
    remains same
  • d)
    increases
Correct answer is option 'D'. Can you explain this answer?

Nandini Patel answered
The electron has negative charge. When an electron is bringing towards another electron, then due to same negative charge repulsive force is produced between them. So, to bring them closer a work is done against this repulsive force. This work is stored in the form of electrostatic potential energy. Thus, electrostatic potential energy of system increases.                 

Alternative: Electrostatic potential energy of system of two electrons                
U=[1/4πε0][(−e)(−e)/r] = [1/4πε0](e^2/r)                
Thus, as r decreases, potential energy U increases. 

If a unit charge is taken from one part to another part over an equipotential surface, then what is the change in electrostatic potential energy of the charge?
  • a)
    10 J
  • b)
    100 J
  • c)
    1 J
  • d)
    0 J
Correct answer is option 'D'. Can you explain this answer?

Equipotential surface means the potential on every. point on that surface is constant. it means the change in potential on equipotential surface is zero we know that... ( electrostatic potential energy = change in potential × charge.)... ... according to this electrostatic potential energy is zero

Equipotential surfaces cannot
  • a)
    be parallel
  • b)
    be spherical
  • c)
    Intersect
  • d)
    be irregularly shaped.
Correct answer is option 'C'. Can you explain this answer?

Krishna Iyer answered
The electric field lines are perpendicular to the equipotential surface. The field lines can not intersect each other because the electric force can not have two directions at a point.

The potential energy of a system containing only one point charge is
  • a)
    Zero
  • b)
    Infinity
  • c)
    Non zero finite
  • d)
    None of the above
Correct answer is option 'A'. Can you explain this answer?

Potential Energy of a System with One Point Charge

  • Definition of Potential Energy: Potential energy is the energy stored in an object due to its position or configuration in a system.

  • Potential Energy of a Point Charge: In the case of a system containing only one point charge, the potential energy of the system is considered to be zero.

  • Explanation: When there is only one point charge in a system, there is no other charge or external force interacting with it to create potential energy. Therefore, the potential energy of a single point charge is considered to be zero.
This is why the correct answer is A: Zero.

If the potential difference between the plates of a capacitor is increased by 0.1%, the energy stored in the capacitor increases by very nearly
  • a)
    0.1%
  • b)
    0.144%
  • c)
    0.11%
  • d)
    0.2%
Correct answer is option 'D'. Can you explain this answer?

Amar Shah answered
**Explanation:**

To understand why the correct answer is option 'D', let's consider the equation for the energy stored in a capacitor:

**Energy (E) = 1/2 * C * V^2**

where E is the energy, C is the capacitance, and V is the potential difference (voltage) across the capacitor plates.

According to the question, the potential difference between the plates of the capacitor is increased by 0.1%. Let the initial potential difference be V1 and the increased potential difference be V2.

**Change in Potential Difference = (V2 - V1) = 0.1% of V1**

Using this information, we can write the new potential difference as:

**V2 = V1 + (0.1/100) * V1 = V1 + 0.001 * V1 = (1 + 0.001) * V1 = 1.001 * V1**

Next, we need to find the change in energy stored in the capacitor. Let the initial energy be E1 and the increased energy be E2.

**Change in Energy = (E2 - E1) = ?**

Using the equation for energy, we can write the new energy as:

**E2 = 1/2 * C * V2^2 = 1/2 * C * (1.001 * V1)^2 = 1/2 * C * (1.001^2) * V1^2**

Now, let's calculate the change in energy:

**Change in Energy = (E2 - E1) = 1/2 * C * (1.001^2) * V1^2 - 1/2 * C * V1^2**

Simplifying this expression:

**Change in Energy = 1/2 * C * V1^2 * (1.001^2 - 1) = 1/2 * C * V1^2 * (1.001^2 - 1)**

To find the percentage increase in energy, we need to divide the change in energy by the initial energy and multiply by 100. Let's calculate:

**Percentage Increase in Energy = (Change in Energy / E1) * 100**

Substituting the expression for change in energy:

**Percentage Increase in Energy = [1/2 * C * V1^2 * (1.001^2 - 1)] / [1/2 * C * V1^2] * 100**

Simplifying this expression:

**Percentage Increase in Energy = (1.001^2 - 1) * 100 = (1.001 * 1.001 - 1) * 100 = (1.002001 - 1) * 100 = 0.2001 * 100 = 0.2%**

Therefore, the energy stored in the capacitor increases by approximately 0.2% when the potential difference between the plates is increased by 0.1%. Hence, the correct answer is option 'D' (0.2%).

If two spheres of different radii have equal charge, then the potential will be
  • a)
    dependent on nature of material of the spheres.
  • b)
    more on smaller sphere
  • c)
    more on bigger sphere
  • d)
    equal on both spheres
Correct answer is option 'B'. Can you explain this answer?

Sushil Kumar answered
When equal charges are given to two spheres of different radii, the potential will be more or the smaller sphere as per the equation, Potential = Charge / Radius.
Since potential is inversely proportional to radius, the smaller radius will have higher potential and vice versa.

The capacitor preferred for high-frequency circuit is 
  • a)
    Air capacitor 
  • b)
    Mica capacitor
  • c)
    Electrolytic capacitor 
  • d)
    None of the above
Correct answer is option 'B'. Can you explain this answer?

Sushil Kumar answered
Mica capacitor. Mica capacitors have low resistive and inductive components associated with it. Hence, they have high Q factor and because of high Q factor their characteristics are mostly frequency independent, which allows this capacitor to work at high frequency.

Negative mutual potential energy corresponds to attraction between two charges
  • a)
    False
  • b)
    True
  • c)
    Can’t predict
  • d)
    None of the above
Correct answer is option 'B'. Can you explain this answer?

Soham Rastogi answered
The formula for electric potential energy of system of 2 charges is (kq1q2)/r, if the result comes out to be negative,one of the charges has to be negative and one has to be positive, because there can be no other case in which it comes out to be negative. Since opposite charges attract each other,hence the answer is True.

A metal sphere carries a charge of 5×10-8C and is at a potential of 200 V, relative to the potential far away. The potential at the centre of the sphere is:​
  • a)
    -100V
  • b)
    0
  • c)
    200V
  • d)
    2×10-6v
Correct answer is option 'C'. Can you explain this answer?

Keerthana Iyer answered
Given data:
Charge on the sphere, q = 5.1 × 10⁻⁸ C
Potential difference, V = 200 V

We know that the formula for potential difference is:
V = kq/r

where k is Coulomb's constant, q is the charge on the sphere and r is the radius of the sphere.

Calculating the radius of the sphere:
r = kq/V
r = (9 × 10^9 Nm^2/C^2 × 5.1 × 10⁻⁸ C) / (200 V)
r = 2.295 × 10⁻⁴ m

The potential at the centre of the sphere is given by:
V' = kq/R
where R is the radius of the sphere.

As the point is at the centre of the sphere, R = r.
V' = kq/r
V' = (9 × 10^9 Nm^2/C^2 × 5.1 × 10⁻⁸ C) / (2.295 × 10⁻⁴ m)
V' = 2 × 10² V

Therefore, the potential at the centre of the sphere is 200 V (option C).

The value of electric field vector along the surface of constant potential of 100 V
  • a)
    100 V/m
  • b)
    -100 V/m
  • c)
    10 V/m
  • d)
    Zero
Correct answer is option 'D'. Can you explain this answer?

Anjana Sharma answered
As we know that electric field is in reverse sense of the directional gradient of electric potential, so if V is constant, E should be zero. So, for E to be zero, either V has to be zero, or constant, or the 3 directional derivative components of V must cancel out each other in space. So we cant claim that V always has to be zero, if E is zero in a region, since E is a vector & V is a scalar quantity. But if V is zero, then surely E has to be zero; the reverse case is not true always.

hope it was helpful...

For any charge configuration, equipotential surface through a point is _____to the electric field at that point.
  • a)
    Perpendicular
  • b)
    At 45 degrees
  • c)
    Anti-parallel.
  • d)
    Parallel
Correct answer is option 'A'. Can you explain this answer?

Rhea Iyer answered
Equipotential surface and Electric field

Equipotential surfaces and electric fields are important concepts in electrostatics. An equipotential surface is a surface on which all the points are at the same potential. Electric field is defined as the force per unit charge experienced by a test charge placed at a point in the electric field.

Perpendicular relationship

The equipotential surface through a point is perpendicular to the electric field at that point. This means that the equipotential surface and the electric field are at right angles to each other at any point on the surface. This relationship is a consequence of the fact that the electric field is a vector field, and the equipotential surface is a scalar field.

Visualizing equipotential surface

To visualize the equipotential surface, imagine a surface through which all points have the same potential. For example, if we have a point charge, the equipotential surfaces will be a series of spherical shells centered on the charge. The potential decreases as we move away from the charge, but any point on a given shell has the same potential.

Visualizing electric field

To visualize the electric field, imagine a vector at each point in space that shows the direction and magnitude of the force that would be experienced by a test charge placed at that point. For example, for a point charge, the electric field lines are radial lines emanating from the charge.

Relationship between equipotential surface and electric field

The relationship between equipotential surface and electric field can be understood in terms of work. When a test charge is moved along an equipotential surface, no work is done because the potential is constant. However, when a test charge is moved along an electric field line, work is done because the potential changes. This means that the equipotential surface and the electric field are always perpendicular to each other.

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