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Previous year question Of Electrostatics For NDA

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Previous year question Of Electrostatics

Previous year question
Q 2714001850

Which one of the following statements is correct with regard to the, material of electrical insulators ?
NDA Paper 2 2017
(A)

They contain no electrons

(B)

Electrons do not flow easily through them

(C)

They are crystals

(D)

They have more number of electrons than the protons on their surface

Solution:

Correct Answer is `=>` (B) Electrons do not flow easily through them
Q 2704212158

Suppose a rod is given a negative charge by rubbing it with wool. Which one of the following statements is. correct in this case?
NDA Paper 2 2017
(A)

The positive charges are transferred from rod to wool

(B)

The positive. charges are transferred from wool to rod

(C)

The negative charges are transferred from rod to wool

(D)

The negative charges are transferred from wool to rod

Solution:

Correct Answer is `=>` (C) The negative charges are transferred from rod to wool
Q 2764512455

A positive charge `+q` is placed at the centre of a hollow metallic sphere of inner radius `a` and outer radius `b`. The electric field at a· distance `r` from the centre is denoted by `E`. In this regard, which one of the following statements is correct ?
NDA Paper 2 2017
(A)

`text(E = 0 for a < r < b)`

(B)

`text(E = 0 for r < a)`

(C)

`E = q/(4piepsi_0 r)` for `a < r < b`

(D)

`E= q/(4piepsi_0a)` for `r < a`

Solution:

Correct Answer is `=>` (B) `text(E = 0 for r < a)`
Q 2303167948

A current of `0.5` A is drawn by a filament of an electric bulb for `20` min. The amount electric charge that flows through the circuit is
NDA Paper 2 2013
(A)

` 1C`

(B)

`10 C`

(C)

`600 C`

(D)

`300 C`

Solution:

It is given that

Current `(I) = 0.5 A`

Time `(t) = 20 min = 1200 s`

We know that,

Charge `(Q) = I xx t`

`=0.5 xx 1200=600 C`
Correct Answer is `=>` (C) `600 C`
Q 2333791642

When long dry hair is brushed the strands often move away from each other because while brushing.
NDA Paper 2 2013
(A)

air is being blown through the strands

(B)

static electric charges are being induced on the hair

(C)

mechanical energy is being transferred into heat energy

(D)

the gravitational attraction among the strands becomes smaller

Solution:

When long dry hair is brushed the strands often move away from each other because while brushing static electric charges are being induced on the hair.
Correct Answer is `=>` (B) static electric charges are being induced on the hair
Q 2384467357

Two similarly charged bodies are kept 5 cm apart in air. If the second body is shifted away from the first by another 5 cm, their force of repulsion will be
NDA Paper 2 2012
(A)

doubled

(B)

halved

(C)

quadrupled

(D)

reduced to one-fourth

Solution:

When long dry hair is brushed the strands often move away from each other because while brushing static electric charges are being induced on the hair.
Correct Answer is `=>` (D) reduced to one-fourth
Q 2335012862

Potential at a point due to a point charge is `V` The charge is doubled and also the distance of the point from the charge is doubled. The new potential is.
NDA Paper 2 2011
(A)

`V/2`

(B)

`4 V`

(C)

`V`

(D)

`2V`

Solution:

Potential, `V = k q/r`

`=> V prop q/r`

`:. (V')/V=(q')/q xx r/(r')`

`=2/1 xx 1/5 =1`

`=> V'=V`
Correct Answer is `=>` (C) `V`
Q 2385145067

If the electrical resistance of a typical substance suddenly drops to zero, then the substance is called.
NDA Paper 2 2011
(A)

super conductor

(B)

semiconductor

(C)

conductor

(D)

insulator

Solution:

Super conductors are those materials whose resistance becomes zero (or almost equal to zero) on cooling below a critical temperature e.g., Mercury below 4.2 K or lead below 7.5 K.
Correct Answer is `=>` (A) super conductor
Q 2325645561

Capacity of a parallel plate condenser can be doubled by
1. doubling the areas of the plates.
2. doubling the distance of separation between the plates.
3. reducing the distance of sepraration between the plates to half the origina separation.
4. doubling both the areas of the plates and the distance of separation between the plates.
Select the correct answer using the codes given below
NDA Paper 2 2010
(A)

1 and 4

(B)

1 and 3

(C)

Only 3

(D)

2 and 3

Solution:

The capacity of a parallel plate capacitor `C=(epsilon_0 A)/d`

`:. C prop A` (area of plates)

and `C prop 1/d` (separation between the plates)

The capacity of a parallel plate condensor can be doubled by doubling the areas of the plate and also by reducing the separation between the plates to half the original separation.
Correct Answer is `=>` (B) 1 and 3
Q 2355645564

If two conducting spheres are separately charged and then brought in contact
NDA Paper 2 2010
(A)

the total energy of tile two spheres is conserved

(B)

the total charge on the spheres is conserved

(C)

botll the total energy and charge are conserved

(D)

the final potential is always the mean of the original potential of tile two spheres

Solution:

When two charged conductors are Joined together through a conducting wire, charge begins to flow from conductor at higher potential to the conductor at lower potential. Due to flow of charge, a loss of energy also takes place in the form of heat through tile connecting wire. So, tile total charge on the spheres is conserved.
Correct Answer is `=>` (B) the total charge on the spheres is conserved
Q 2385156067

A hollow metal ball carrying an electric charge produces no electric field at points
NDA Paper 2 2010
(A)

outside the sphere

(B)

on its surface

(C)

inside the sphere

(D)

only at the centre

Solution:

If we have a charged conducting solid sphere, then total charge resides only on its outer surface and then electric field intensity at any point inside the solid sphere is zero. Therefore, for a hollow metallic ball carrying an charge, the electric field inside it is zero.
Correct Answer is `=>` (C) inside the sphere
Q 2376612576

Net charge in a current-carrying conductor is
NDA Paper 2 2009
(A)

always positive

(B)

always negative

(C)

zero

(D)

either positive or negative

Solution:

If a current passing through any conductor, net charge through any section is zero.
Correct Answer is `=>` (C) zero
Q 2316112979

Non-conductors, whose polarisation is caused by an electric field, are known as
NDA Paper 2 2009
(A)

Semi-conductors

(B)

Super-conductors

(C)

Dielectrics

(D)

Resistive conductors

Solution:

Dielectrics are non-conductors upto a certain value of field depending on its nature. When a dielectric material is placed in the uniform Electric field `E_0` set up between the parallel plates of charged capacitor, the material becomes electrically polarized.
Correct Answer is `=>` (C) Dielectrics
Q 2376123076

The electric charge is stored in a device called
NDA Paper 2 2009
(A)

inductor

(B)

capacitor

(C)

Resistor

(D)

transformer

Solution:

A capacitor is a device which can be used to store the
electrical charge to be used later.
Correct Answer is `=>` (B) capacitor
Q 2386234177

The force experienced by a unit positive test charge placed at a point is called
NDA Paper 2 2009
(A)

magnetic field at that point

(B)

gravitational field at that point

(C)

electrical field at that point

(D)

nuclear field at the point

Solution:

Electric field intensity at any point is defined as the force experienced by unit positive charge placed at that point.
Correct Answer is `=>` (C) electrical field at that point
Q 2316380270

Which one of the following is correct? Lightning is formed, when
NDA Paper 2 2007
(A)

similar charges of electricity rush towards each other and then get repelled

(B)

clouds strike against impurities in air and the friction burns up these impurities

(C)

strong opposite charges in different clouds break down the resistance offered by intervening air

(D)

water vapour produces electricity in the clouds

Solution:

Lightning is formed when similar charges of electricity rush towards each other and then get repelled.
Correct Answer is `=>` (A) similar charges of electricity rush towards each other and then get repelled
Q 2306380278

Which one of the following is correct? Electrical lines of forces
NDA Paper 2 2007
(A)

exist everywhere

(B)

exist in the immediate vicinity of positive charge

(C)

exist in the immediate vicinity of negative charge

(D)

are imaginary

Solution:

An electric line of force is an imaginary line or curve drawn through a region of space so that a tangent drawn at any point of the curve gives the direction of electric field vector at that point.
Correct Answer is `=>` (B) exist in the immediate vicinity of positive charge
Q 2376380276

Two similar poles repel each other with a force of 0.005 N when placed `16 cm` apart. If they are placed `8 cm` apart, what will be the repulsing force?
NDA Paper 2 2007
(A)

`0.001 N`

(B)

`0.002 N`

(C)

`0.01 N`

(D)

`0.02 N`

Solution:

By Coulomb's law,

`F=1/(4 pi in_0)(q_1q_2)/r^2`

or, `F prop (q_1q_2)/r^2` or `F prop 1/r^2`

`=> F_2F_1=(r_1/r_2)^2=(16/8)^2=4`

`=>F_24F_1=4 xx 0.005=0.02 N`
Correct Answer is `=>` (D) `0.02 N`
Q 2316191070

Which one of the following is correct? A negatively charged glass rod has always.
NDA Paper 2 2007
(A)

less electrons than protons

(B)

less electrons than neutrons

(C)

less protons than electrons

(D)

less neutrons than protons

Solution:

A negatively charged glass rod has always less number of protons and has more number of electrons.
Correct Answer is `=>` (C) less protons than electrons
Q 2306291178

In our houses, we get `200` V AC. What does the value `220` V represent?
NDA Paper 2 2007
(A)

Constant voltage

(B)

Effective voltage

(C)

Average voltage

(D)

Peak voltage

Solution:

`220` V AC represents the virtual value of voltage0
Correct Answer is `=>` (B) Effective voltage
Q 2366391275

A hollow sphere of radius 50 cm is charged, such that the potential on its surface is 500 V. What is the potential at the centre of sphere!'
NDA Paper 2 2007
(A)

zero

(B)

`10 V`

(C)

`200 V`

(D)

`500 V`

Solution:

In a hollow conducting sphere, potential at the surface and at the centre of the sphere is same, i.e., `500 V`.
Correct Answer is `=>` (D) `500 V`
 
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