Electrostatics DEMO

Explanation A
Slope = Q/V = C

Explanation D
Coulomb’s force is a mutual force. It means that if a charge ‘q₁’ exerts a force on charge ‘q₂’. Then ‘q₂’ also exerts an equal and opposite force on ‘q₁’.
If charge ‘q₁’ exerts an electrostatic force ‘F₁₂’ on charge ‘q₂’ and ‘q₂’ exerts electrical force ‘F₂₁’ on charge ‘q₁’ and then
F₁₂ = –F₂₁

Explanation: B
FUNCTION
i. Capacitors store electrical charge.
ii. They are used in timing circuits because it takes time for a capacitor to fill with charge.
iii. They are used to smooth varying DC supplies by acting as a reservoir of charge.
iv. They are used in filter circuits because capacitors easily pass AC (changing) signals but they block DC (constant) signals.

Explanation: B
The field lines of a single negative charge are radially inward

Explanation A
Total charge required 1 Coulomb
∴ q = 1C
since q = ne
⟹ n = q/e
⟹ n = 1/1.6×10^-19
⟹ 6.25×10¹⁸  

Explanation C
The capacitance depends on the geometry of the capacitor and capacitance of a capacitor is affected by the area of the plates, the distance between the plates, and the ability of the dielectric to support electrostatic forces.

Explanation B
Charge at rest produces only electric field

Explanation C
C = Aε_o/d, increases of its area.
C ∝ A

Explanation C
K.E = q∆V = 2e × 200V = 400eV

Explanation D
k is a constant of proportionally known as the Coulomb constant, having the value 9×10⁹ Nm²/C² .

Explanation: A
Coulomb’s law is given by equation
F = kq₁q₂/r²
from this we can obtain the unit of k as Nm²C^-2

Explanation B

Explanation D
On equipotential surface work done always zero

Explanation B

Explanation D
C depends on Area.
C = Aε_o/d

Explanation: A
RC value is called time constant and determine the time how slow or fast a capacitor will charge or discharge

Explanation C
K.E = q∆V = 1e × 1V = 1eV

Explanation: B
Electric potential is equals to the work done in moving a charge from one point to another in an electric field.

Explanation: C
Gauss’s law states that the flux through any closed surface is 1/∈_o times the total charge enclosed in it.

Explanation C
Due to earthed V=0

Explanation: D
Electric field exerts force only on charge particles.

Explanation: A
Vectors and Scalars
Some quantities in physics, such as time, distance, mass, speed, temperature, etc., just need one number to specify them. These are called scalar quantities.
On the other hand, many quantities are fully specified only if, in addition to a number, a direction is given. Examples are velocity, acceleration, force, etc. These are called vector quantities.

Explanation: C

Explanation: D
Let  is separation between +2μC and -2μC. Net potential due to both charges at mid-way between “P” and “Q” is

Explanation: D

Explanation: C
Voltage(V)
◈ Measured in volts (V) using a voltmeter
◈ 1 volt = 1 joule/coulomb

Explanation: B
In  units, the value of permittivity of free space is
ε₀ = 8.85 × 10^-12 C² N^-1 m^-2

Explanation: D

“k” is the constant of proportionality Its value depends upon the nature of the medium between the two charges and the system of units

Explanation: B

Explanation: B

Explanation: B
C = A∈₀/d
above relation describes that if area of plates is halved and their separation is reduced to one third, the capacitance will become 1.5 times.

Explanation: C
Coulomb’s law is given by
F = kq₁q₂/r²
Applying the conditions
F = k × 2q₁ × 2q₂/ (1/2r²)
F = 16 (kq₁q₂/r²)

Explanation: C

Explanation: C
F_med = F_vac/ε_r = 4/2 = 2N

Explanation: D
t = RC = (5×10⁶) (2×10^-6) = 10s

Explanation: B
Unit of 1eV is joule.

Explanation: C
Φe = EA ⇒ E = Φe/A

Explanation: B
Point X, Y and Z lie in the uniform electric field. So, at these points electric force on any charge particle will be same.

Explanation: D

Explanation: D

The vector sum of all the forces acting on a charge placed at the center of the circle is zero.

Explanation: D

Explanation: A

Explanation: D
E = ΔV/d ⇒ E ∝ ΔV
ΔV₁ = 90 V
ΔV₂ = 50 V
ΔV₃ = 100 V
ΔV₄ = 60 V
E₂ < E₄ < E₁ < E₃

Explanation: A
W = q∆V
on equi-potential surface ΔV = 0
W = 0
(Electric filed is a conservative field. So, work done along closed path is zero.)

Explanation: C
when a dielectric inserted between the plates of charged parallel plates capacitor
i.  Charge remains same
ii.  Electric field decreases
iii. Potential difference decreases
iv. Capacitance increases
. Energy stored in capacitor decreases

Explanation: D

Explanation: C

Explanation: C
K.E = q∆V ⇒ K.E ∝ q
(for same potential difference) As
q_α > q_P = q_e

Explanation: B
W = qV
⇒ q = W/V = 1000/20 = 50C

Explanation A
E = F/q. So its units are N/C.

Explanation B
any surface over which the potential is constant is called an equipotential surface. In other words, the potential difference between any two points on an equipotential surface is zero. Work done in moving a charge over an equipotential surface is zero.

Explanation C
Electric force depends on medium while gravitational force does not.
Gravitational force between two point objects is directly proportional to the product of masses, inversely proportional to square of distance between them and acts along the line joining them.

G is known as the universal gravitational constant.
◈ Does not depend on the nature of bodies
◈ Does not depend on temperature
◈ Does not depend on the medium between the particles

Explanation C
Through the application of Gauss’s law we get the intensity = σ / 2ε₀.

Explanation B
V = J/C , if J = 5, C = 1 then V = 5 V

Explanation D
The capacitance of a capacitor is affected by the area of the plates, the distance between the plates, and the ability of the dielectric to support electrostatic forces.
Larger plates provide greater capacity to store electric charge.

Explanation B
W= q V = 0.01 ⨯ 1000 = 10 J.

Explanation C
E = F/q Electric field intensity is force per unit charge.

Explanation: B

Explanation A
Capacitors store electric energy.

Explanation D
The only pair of charged bodies that would attract one another is the pair of unlike charged spheres. The rest of the pairs are like charges, which repel one another.

Explanation A
Presence of di-electric always reduces the electrostatic force between charged particles as compared to free space by a factor known as relative permittivity. Represented by ε_r.

Explanation A
Capacitance increases when a di-electric is place between the capacitor plates.

Explanation A
Potential of 1 V exists between two points if work done in moving a unit positive charge from one point to other, keeping equilibrium, is 1 J. or 1 V = 1J/1C or J = VC.

Explanation D
All these statements are correct. E has only one direction at a given point so the lines never cross each other.

Explanation D
Q = CV = 2⨯10^-6 ⨯12 = 24 μC

Explanation B
The minimum possible value of charge is the charge of electron i.e. 1.6×10^-19 C.

Explanation A
The SI units of the field are N⋅C⁻¹ or, equivalently, volts per meter (V⋅m⁻¹)

Explanation C
F = 9 × 10⁹ * q₁ * q₂ / r²;
q₁, q₂ and r are all equal to one. So F = 9 × 10⁹ N.

Explanation B
As insulator plate is passed between the plates of the capacitor, its capacity increases first and then decreases as the plate slips out. As a result, positive charge on plate A increases first and then decreases, hence, current in outer circuit flows from B to A and then from A to B.

Explanation C
Presence of dielectric reduces the electrostatic force by the factor of relative permittivity. So the medium with lowest value of relative permittivity shall have highest force. 

Explanation D
by putting area double and separation half, the capacitance becomes 4 as shown below.
C = ε 2A / (1/2)d
= ε 4A/d

Explanation B
Total capacitance = C₁C₂ / (C₁ + C₂)
for calculating net capacitance, capacitance in series behave just like resistances in parallel.

Explanation C
The time constant is defined as the time it takes for the capacitor to deplete 36.8% (for a discharging circuit) of its charge or the time it takes to reach 63.2% (for a charging circuit) of its maximum charge capacity

Explanation D
Capacitance is added when connected in parallel. \

Explanation D
if the electric field is zero throughout a region of space, the electric potential must be constant throughout that region

Explanation B
In RC circuits, smaller values of time constant RC leads to more rapid discharging.

Explanation B
Only i and ii are correct. Electrical force is medium dependent while gravitational force is not. Another difference is that electrical forces can be attractive or repulsive while gravitational force is always attractive. 

Explanation D

Explanation A
We do not want the test charge to distort the electric field that it is measuring so it has be very small. 

Explanation A

Explanation A
Radially Outward

because an electric field has both magnitude and direction, the direction of the force on a positive charge is chosen arbitrarily as the direction of the electric field. Because positive charges repel each other, the electric field around an isolated positive charge is oriented radially outward

Explanation A
E → uniform inside so no work done.

Explanation D
MΩ × pF =?
10⁶Ω × 10^-12F = µs
µ = 10^-6

Explanation: C
The value of relative permittivity for all the dielectrics other than air or vacuum is always greater than unity.

Explanation: A

Explanation D
If the charge on the electron is e = 1.6 × 10^-19 C. Then in 1 coulomb of charge there will be
number of electrons = 1/1.6 × 10^-19 
which is 6.2 × 10¹⁸ electrons.

Explanation: A
RC = t ⇒ C = t/R

Explanation: B
The amount of charge on both plates of the capacitor will be same. If one plate has +Q charge then other will be -Q.

Explanation: C

Explanation: C
The automobiles wind shield wipers works on charging and discharging of capacitor.

Explanation B
Capacitance in parallel is C + C = 2C.
Capacitance in series is = C/2
Ratio = 2C / (C/2) = 4 : 1

Explanation: A
F = qE = (2×10^-2 )(400) = 8N

Explanation: D

Explanation: C
Cs = C/60
Cp = 60C
Cs/Cp = 1/3600

Explanation: C
New charges
q₁ = -2C & q₂ = 2C
F ∝ q₁q₂
F = 4N
as q₁q₂ are opposite charges their force is attractive

Explanation: D

Explanation: B

Explanation: C

Explanation: D

Explanation: C

Explanation: B
Two charges are placed a certain distance apart in air. If a glass slab is introduced between them, the force between them will decreases. 

Explanation: B
In Coulomb’s law, permittivity constant of material comes in the denominator.
Since a metallic sheet is put in between and metals are good conductors, the permittivity is greatly increased and hence the force between two charges will decrease.

Explanation: D
Both the spheres are connected and when both the potentials are equal then there is no current flow between them

Explanation: A
Variation of different variables (Q, C, V, E and U) of parallel plate capacitor when dielectric (K) is introduced when battery is removed is 
C′=KC                  E′=E/K
Q′=Q                    U′=U/K
V′=V/K
Only the amount of charge stored in the capacitor will remain conserved when the dielectric is inserted between the plates.

Explanation: C

Explanation: C
When the charge given to a capacitor is doubled its capacitance does not changes. The capacitance depends only on the geometrical configuration of your conductors (capacitors).

Explanation: D

We know that electric field strength is the negative gradient of potential.

⇒ E = – (dV/dr)

Given that the potential difference is 12 volts and distance between the two charged plates is 0.005 metre.

Substituting we get

⇒ E = – (12/0.005) = -2400 Vm⁻¹

⇒ As Potential Gradient is negative of the Electric field strength.

⇒ The Potential gradient between the two plates = 2400 Vm⁻¹

Explanation C

Explanation B

Explanation: B
The concept was introduced into physics in the 1830s by the English scientist Michael Faraday, who considered magnetic and electric effects in the region around a magnet or electric charge as a property of the region rather than an effect taking place at a distance from a cause.

Explanation: D
Potential difference: The difference of potentials at two points in an electric field is called potential difference. Or, The amount of work done in transferring a unit positive charge from one point to another point in an electric field is called potential difference between the two points.
Let the potentials at two points A and B in an electric field is V_A and V_B respectively. Then
V_B – V_A = ∆V = W_AB/q_o = W/q_o

Explanation: B
Electric Fields
◈ Electric fields are represented by electric field lines (imaginary) and show the direction of the force at that point.
◈ Electric field direction is from a positive charge to a negative charge.
◈ Electric field lines (also known as electric flux) do not touch each other.
◈ Electric field line represents the path a small positive charge would move in the electric field.

Explanation: C 
Selenium is a good conductor of electricity in presence of light. This phenomenon is called photoconductivity.
Used as a photoconductor in photocopiers and also in an X-ray imaging technique known as xeroradiography for decades.

Explanation: D
Electrostatics is the study of electric fields in static equilibrium. In addition to research using equipment such as a Van de Graaff generator, many practical applications of electrostatics exist, including photocopiers, laser printers, ink-jet printers and electrostatic air filters.

Explanation: D
Vacuum permittivity, commonly denoted ε₀ (pronounced as “epsilon nought” or “epsilon zero”) is the value of the absolute dielectric permittivity of classical vacuum. … ε₀ = 8.8541878128(13)×10⁻¹² F⋅m⁻¹ (farads per meter).

Explanation: C
The units of “ε_o” are reciprocal of the units of “k”.

Explanation: B
The study of charges at rest under the action of the electric force is named as electrostatics.

Explanation: D

Explanation: B
Electric field strength is defined as:

Explanation: C

Explanation C

Explanation: B

Explanation: A

Explanation: B

Explanation: D