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# 10th Class Chapter 4 Physics Long Questions

Dear students, prepare for physics class 10th chapter 4 long questions. These important long questions are carefully added to get you best preparation for your 10th class physics ch. 4 exams.

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##### Question: 1
<div>What is meant by electric field and electric field intensity with help of example?</div><div><br></div>
1-52

Electrostatic induction:

In the presence of a charged body an insulated conductors develops positive charge at one end and negative charge at the other end this process is called the electrostatic induction.

Experiment:

Consider a metallic sphere placed on an insulated stand. the sphere is neutral as it carries equal number of positive and negative charges now bring a negatively charged rubber road near the conducting sphere left part of the sphere that is closed to the rod becomes positively charged while the right part that is away from the rod becomes negatively charged. Negative charge in the rod repelas the negative charge of the sphere and shifts it to the opposite sign region of the sphere that is away from the rod .But as a whole the sphere is still neutral, since no charge has been added subtracted .Now if we remove the rod away from the sphere the charges again will spread uniformly on the whole surface of the sphere.

##### Question: 2
<div>Two point charges q1=10uc and q2=5 uc and placed at a distance of 150cm find the coulomb's force between them. also find the direction of this force?</div><div><br></div>
2-52

Given Data:

Q1= 10 uc

= 10*10-6c

Q2 5 uc

= 5*10-6c

R = 150cm =1.5m

K = 9109 Nm2C2

F=?

Solution:

As we know that:

F= k q1 q2/r

Putting values we get

F = (9*10/9) *510/6*10*10-

(1.5)2

= 9*5*10/9-6 +1-6

2.25

= 45 *10-2

2.25

F= 0.2 N

##### Question: 3
<div><br></div><div><br></div><div><br></div><div>Explain briefly electrostatic induction?</div>
3-52

Electric field:

The electric field of a charge is a region around a charge in which it exert electrostatic force on an other charge.

Explanation:

Consider a positive carge q and bring a test carge q/0 will experience a force .According to coulomb’s law the value of this force will depend upon the distance between two charges.

If charge q/0 is moved away from q this force will decrease till a certain distance the force would practically reduce to zero.

Electric field intensity:

The strength of electric field at any point in space is called electric field intensity .

Explanation:

If f is the force acting on test charge q/0 the electric field intensity would be,

F = f/q0

If the electric field due to a given arrangement of charge is known at same point, the force on any particle with charge q placed at that point can be calculated by using the formula,

F= qe …… This I force acting on a unit positive charge placed at that point.

Unit:

SI unit of electric field intensity is NC-1

Quantity:

Electric intensity being a force is a vector.

##### Question: 4
<div>Two capacitors of capacitance 6u F and 12u F are connected in series with 12 v battery.find the equivalent capacitance of the combination. Find the charge and the potential across each capacitor?</div><div><br></div><div><br></div>
4-52

Given Data:

C1 = 6uf

= 6*10-6f

C2 = 12UF

= 12*10-6F

V= 12 volt

Ce =?

V1 = ?

V2 = ?

Q1 = ?

Q2 = ?

Solution:

We know that,

1/Ce = I/C1+I/C2

I/Ce = I/6+ 1/12

= 2+1

12

= 3/12

1/Ce = 1/4

Ce =4uf

Ce = 4*10-6 f

Q = Cev

= 4*10-6*12

= 48*10-6

Q = 48uc

Zn series combination charge across each capacity is same so,

Q =Q1=Q2+V1 = Q1/C1

= 48*10-6/6*10-6

V1=8 volts

V2 = Q2/C2

= 48 *10-6/12*10-6

V2 = 4 volts.

##### Question: 5
<div><div>Two capacitors of capacitance 6u F and 12u F are connected in series with 12 v battery.find the equivalent capacitance of the combination. Find the charge and the potential across each capacitor?</div><div><br></div><div><br></div></div><div><br></div>
5-52

Given Data:

C1 = 6uf

= 6*10-6f

C2 = 12UF

= 12*10-6F

V= 12 volt

Ce =?

V1 = ?

V2 = ?

Q1 = ?

Q2 = ?

Solution:

We know that,

1/Ce = I/C1+I/C2

I/Ce = I/6+ 1/12

= 2+1

12

= 3/12

1/Ce = 1/4

Ce =4uf

Ce = 4*10-6 f

Q = Cev

= 4*10-6*12

= 48*10-6

Q = 48uc

Zn series combination charge across each capacity is same so,

Q =Q1=Q2+V1 = Q1/C1

= 48*10-6/6*10-6

V1=8 volts

V2 = Q2/C2

= 48 *10-6/12*10-6

V2 = 4 volts.

##### Question: 6
<div>How are capacitors connected in series? Describe the characters features of the combination.</div><div><br></div>
6-52

In this combination capacitors are connected side by side i.e the right plate of one capacitors is connected to left plate of next capacitors.

Characteristics:

Each capacitor has the charge it battery supplies to charge to the left plate of the capacitor q., due to induction – Q charge is induced on its right plate i.e,

Q1=Q2=Q3=Q

The potential difference across each capacitor is different due to different value of capacitances.

The battery voltage has been divided among the various capacitors .Henc

= V1+V2+V3

Q=CV

V=Q/C

Q/C1+Q/C2+Q/C3

=Q ( I/C1 +I/C2+I/C 3)

Q= CV

V/Q =I/C

I/C= I/C1+I/C2+I/C3

Series combination of capacitors can be replaced with one equivalent capacitors having capacitance

= I/C1+I/C2+I/C3

If N capacitors are connected on series then

= I/C1 +I/C2+I/C3+-------+I/Cn

Equivalent capacitance of a series combination of capacitors is smaller than any individual capacitance ,capacitors connected in series decrease the value of capacitance.

##### Question: 7
Two bodies are oppositely charged with 500 uc and 100 uc find the force between the two charges if the distance between them in air i 0.5m?
7-52

Given Data:

Q1= 500 uc

=500*10-6 C

Q2 = 100 uc

= 100*10-6 C

R =0.5m

K= 9*10-9 Nm2C-2

F= ?

Calculations:

According to coulomb’s law,

F= k q1 q2/r

Putting values we get

= 9*10-9/500*10-6*100*10-6

(0.5)2

= 9*5*10-910-210-610-2*10-6

(0.5) (0.5)

= 45*10/9+2+6+2+6

0.25

= 45*10

0.25

F = 1800 N

##### Question: 8
<p class="MsoNormal">Define electrostatic induction electrostatic induction?</p>
8-52

In the presence of a charged body an insulated conductor develops positive charges at one end and negative charges at their other end this process is called electrostatic induction.

##### Question: 9
<p class="MsoNormal">What is electroscope?</p>
9-52

The gold leaf electroscope is a sensitive instruments used for detecting and testing the nature of charges on a body.

##### Question: 10
<p class="MsoNormal">What is the difference between capacitor and dielectric?</p>
10-52

A device used for storing electric charge is called a capacitors the air or insulator placed between the plates of a capacitors is called dielectric.

##### Question: 11
<p class="MsoNormal">Define charge and types of charge?</p>
11-52

Charge is the basic property of the material body due to which it attracts or repels another body and there are two types of the charges one is positive and second I negative.

##### Question: 12
<p class="MsoNormal">Define coulomb’s law write mathematical form ?</p>
12-52

The force of attraction or repulsion between two point charges is directly proportional to the product of the quantity of charges and inversely proportional to the square of the distance between them.

F= k q1 q2/r2

##### Question: 13
<p class="MsoNormal">Define electric field and electric field intensity write its unit?</p>
13-52

A region around a charge in which it exerts electrostatic force on another charge.

Electric field intensity:

The force acting on a unit positive charge placed at a point its SI unit is NC-1.

##### Question: 14
<p class="MsoNormal">What is meant by point charge?</p>
14-52

If the distance between two charge is much greater as compared to their size then these bodies are considered as point charge.

##### Question: 15
<p class="MsoNormal">Write the names of different types of capacitors?</p>
15-52

· Paper capacitors

· mica capacitors

· Parallel plate capacitor

· Electrolytic capacitors

##### Question: 16
<p class="MsoNormal">What is electric field lines?</p>
16-52

The direction of electric field of lines intensity in an electric field can also be represented by drawing lines these lines are known as electric field lines.

##### Question: 17
<p class="MsoNormal">What is potential difference and write its name of unit?</p>
17-52

The energy supplied by the unit charge as it moves from one point to the other in the direction of the field the unit of potential difference is volt.

##### Question: 18
<p class="MsoNormal">What is electric potential?write its unit?</p>
18-52

Electric potential at a point in an electric field is equal to the amount of work done in bringing a unit positive charge from infinity to that point its unit is volt or JC-1

##### Question: 19
<p class="MsoNormal">Describe the construction of capacitors?</p>
19-52

It consist of two thin metal plates,parallel to each other separated by a very small distance the medium between the two plates is air or a sheet of some insulator this medium is known as dielectric.

##### Question: 20
<p class="MsoNormal">Does each capacitor carry equal charge in series combination explain?</p>
20-52

Each capacitor has the same charge across each capacitor in series combination if battery supplies +Q charge to the left plate of the capacitors CL,due to induction –‘Q’ cargeharge is induced on its right plate and +Q charge on the left plate of the capacitors i.e on each plate of capacitors charge is same.

##### Question: 21
<p class="MsoNormal">Write two uses of capacitors uses of capacitors?</p>
21-52

They are used for table fans, ceiling fans, coolers motors and washing machines they are used in electronic circuits of computers.

##### Question: 22
<p class="MsoNormal">What is gold leaf electroscope?</p>
22-52

The gold leaf electroscope is a sensitive instruments used for detecting and testing the nature of charges on a body.

##### Question: 23
<p class="MsoNormal">What is difference between fixed and variable capacitors?</p>
23-52

Fixed capacitors;

If the plates of the capacitors are immoveable then such capacitors are called fixed capacitors the capacitance of the such capacitor can not be changed.

##### Question: 24
<p class="MsoNormal">What do you mean by the capacitance of a capacitor?</p>
24-52

It is the ability of the capacitors to store charge when one coulomb of charge given to the plates of the capacitor produces a potential difference of one volt between the plates of the capacitor.

##### Question: 25
<p class="MsoNormal">Define the unit of capacitance?</p>
25-52

The unit of capacitance is fared if one coulomb of charge given to the plates of a capacitor produces a potential difference of one volt between the plates of the capacitor then its capacitance would be one farad.

##### Question: 26
<p class="MsoNormal">What are hazards of static electricity?</p>
26-52

The phenomenon of lightning occurs due to a large quantity of electric charge which build up in the heavy thunderclouds the thunder clouds are charged by friction between them water molecules in the thunderclouds and the air molecules.

##### Question: 27
<p class="MsoNormal">Draw circuit diagram for three capacitors circuit connected in series combination?</p>
27-52

I/Ceq = I/C1 + I/C2 +I/C3

C1 C2 C3

K + V

##### Question: 28
<p class="MsoNormal">How energy stored in a capacitors?</p>
28-52

If a capacitor is connected to a battery of V, then the battery transfers a charge +Q from plate A to plate B so that –Q charge appears on plate B and +Q charge appears on plate A. The charge on each plate attract each other and thus remained bound with io the plate , in this way charge is stored in a capacitors for long time.

##### Question: 29
Write the formula of parallel combination of capacitors?<div><br></div>
29-52

The formula of parallel combination of capacitor is Ceq = C1+2+C3 +----Cn

##### Question: 30
<p class="MsoNormal">What is mica capacitor?</p>
30-52

Mica capacitor is an example of fixed capacitors Zn mica capacitor , mica is used as dielectric between the two metal plates mica is enclosed in a plastic case.

##### Question: 31
<p class="MsoNormal">How electric potential and potential energy relate with electric field?</p>
31-52

The relation between electric potential and potential energy is given by V = W/q.

##### Question: 32
<span style="font-size:11.0pt;line-height:107%; font-family:&quot;Calibri&quot;,sans-serif;mso-ascii-theme-font:minor-latin;mso-fareast-font-family: Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin; mso-bidi-font-family:&quot;Times New Roman&quot;;mso-bidi-theme-font:minor-bidi; mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">What is electric charge? How objects can be electrified?</span>
32-52

We have learnt already that an inherent property of an object is its mass. An object with smaller mass will have less inertia as compared to an object with larger mass. Along with mass, another inherent property of an object is its electrical charge. Charge is measured in units of coulomb ©

There are two kinds of charges:

A simple experiment can be performed to show that there are two types of charges, one type is called positive and the other negative.

There are two types of charges and similar charges repel and different charges attract.

Interestingly it is seen that after rubbing the silk cloth and animal fur also acquired the charge in opposite sense to glass rod and rubber rod respectively. `Structure of Atom’ we learnt that all matter is made up of atoms. Atoms have two kinds of charges: protons contained in the nucleus of atom have positive charge, whereas electrons clouding around the nucleus carry negative charge, neutrons inside the nucleus have no charge. The charge on an electron or proton is said to be an elementary or fundamental charge because all known charges are made up of electrons and protons and so all charges are integer multiples of the fundamental charge.

As all the matter is made of atoms, thus every material object has charges in it. We often do not notice the effects of electrical charges because most objects have the same number of electrons and protons in them (therefore we have equal and opposite charges) and as a result the net effect is zero and so these objects are electrically neutral

Electrification:

Electric charge is not created in the process of charging object, charges are only transferred between the objects. In electrification experiments It is seen that silk cloth/animal fur also attained charge. Thus, in those experiments, charge was not produced rather it was only transferred and we can say that objects can be charged by removal or addition of charges (specifically electrons) called electrification.

##### Question: 33
<span style="font-size:11.0pt;line-height:107%; font-family:&quot;Calibri&quot;,sans-serif;mso-ascii-theme-font:minor-latin;mso-fareast-font-family: Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin; mso-bidi-font-family:&quot;Times New Roman&quot;;mso-bidi-theme-font:minor-bidi; mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">What is electrostatic induction? Explain.</span>
33-52

A change in distribution of electrical charge in an object, caused by the influence of nearby charges is called electrostatic induction. This effect may be shown by bringing a negatively charged rubber strip near to an insulated metal sphere X which is touching a similar sphere Y. Electrons in the spheres are repelled to the far side of Y.

If X and Y are separated, with the charged strip still in position, X is left with a positive charge (deficient of electrons) and Y with negative charge (excess of electrons). In this way electrostatic induction can be used to charge objects.
##### Question: 34
<span style="font-size:11.0pt;line-height:107%; font-family:&quot;Calibri&quot;,sans-serif;mso-ascii-theme-font:minor-latin;mso-fareast-font-family: Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin; mso-bidi-font-family:&quot;Times New Roman&quot;;mso-bidi-theme-font:minor-bidi; mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">What is the function of electroscope? How can we use electroscope to find the presence and nature of charge on a body?</span>
34-52

Electroscope is a device used for detecting and testing the nature of charge on a body. It works on the principle that similar charges repel each other.

A simple form of electroscope consists of a metal bar which has a metallic sphere (ball) at its upper end. Thin flexible metal leaf ( made of gold, silver, copper or any other metal ) is attached to the lower end of metal bar.

The lower part is enclosed in an insulated housing.

Working:

In order to detect charge on a body we touch the metal ball with it. For example, if we touch it with negatively charged rubber rod some of its excess electrons will be transferred to the ball and then they will spread throughout the metal rod and the metal foil. The flexible metal leaf will be repelled by the similar change on the metal rod and will move away from the rod by rising higher , As more electrons are transferred to the electroscope, the metal leaf will rise higher, Alternatively if the rod id positively charged it will attract electrons from the electrons from the electroscope, leaving a net positive charge on it. Once again the foil will rise.

However to test the nature of charge on the body we charge the electroscope with some known charge first. Now if the same charge is added to the metal ball, it will increase divergence of flexible metal leaf and opposite charge will decrease the divergence allowing us to identify the unknown charge on the body

##### Question: 35
<p class="MsoNormal">State and explain Coulomb’s Law.?<o:p></o:p></p>
35-52

Coulomb's lawstates that: The magnitude of the electrostatic force of attraction or repulsion between two point chargesisdirectly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them. The forceisalong the straight line joining them

Statement: The electric force between two stationary point charges is directly proportional to the product of the charges; inversely proportional to the square of the distance between them and is directed along the line joining these charges.

The attraction of an uncharged object by a charged object near it is due to electrostatic induction. For example, it is the reason for the opening question `why after running a plastic comb through our hair on a dry day does the comb attract small pieces of paper?’. The influence of the charge on the comb redistributes the charges in the paper due to electrostatic induction.

Charges in the pieces of paper with the same sign (polarity) are pushed away while charges with opposite sign are pulled closer. Thus change in distance means the attractive force due to the closer opposite sign charges is greater than the repulsion due to the same sign charges which have been pushed further away. As coulomb forces decreases as distance between similar charges is increased, on the other hand it increases for dissimilar charges, as a result it overcomes inertia and lifts small pieces of paper. This creates a net attractive force which pulls the paper towards the comb.

##### Question: 36
<span style="font-size:11.0pt;line-height:107%; font-family:&quot;Calibri&quot;,sans-serif;mso-ascii-theme-font:minor-latin;mso-fareast-font-family: Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin; mso-bidi-font-family:&quot;Times New Roman&quot;;mso-bidi-theme-font:minor-bidi; mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">What is meant by electric field and electric field intensity? How the field lines represent the electric field for isolated positive and negative point charges</span>
36-52

Electric Field and Its Intensity:

The region around a charge in which an electric test charge would experience an electric force is called electric field, And the strength a of the field (equal to the force experience by a (+1C) test charge) at any point is called electric field intensity.

An electric field exist in the region of space around a charged object in three dimensions. When another charged object enters this electric field, an electric forcer acts on it even without any physical contact between the charges.

Consider a small positive test charge qo near the greater magnitude charge q Now the electric field E at any point in space is defined as the force F acting on unit positive charges qo , divided by the magnitude of the test charge qo , mathematically

E =FE/qo equation (1)

Equation (1) gives the mathematical form of electric field intensity. The SI unit of electric field intensity is newton per coulomb (NC). It is a vector quantity having direction in which a positive test charge would move under the influence of force.

An easy way to visualize an electric field is to draw lines that follow the same direction as the electric field intensity vector E at any point. These lines are called electric field lines.

Electric field intensity vectors help to visualize the electric field. Electric field lines are a kind of “map” That gives the direction and strength of the field at various places. The direction of the lines is radially outward for a positive charge and radially inward for a negative charge.

##### Question: 37
<span style="font-size:11.0pt;line-height:107%; font-family:&quot;Calibri&quot;,sans-serif;mso-ascii-theme-font:minor-latin;mso-fareast-font-family: Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin; mso-bidi-font-family:&quot;Times New Roman&quot;;mso-bidi-theme-font:minor-bidi; mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">What is electric potential? In what units we measure electric potential?</span>
37-52

Electric Potential:

The electric potential energy `U’ per unit charge `q’ in an electric field is called electric potential V

V= U/q= W/q Equation (1)

The electric potential units of joules per coulomb (J C), or volt. (V) in honor of Italian scientist Alessandro Volta. The potential at a point is one bolt, when it requires one joule of work to move a positive charge of one coulomb form a point of ZERO potential to that point.

1volt = 1joule/1coulomb

The concept of electric potential is closely related to electric field. Electric field is the force per unit charge, whereas the electric potential is the energy per unit charge. However electric potential is a scalar quantity, since, it is easier to solve problems with scalars, therefore, and it is simpler to solve problems with electric potential rather than electric field.

Let us consider a positive charge +q is placed in an electric field at point B. If the charge is allowed to move freely, it will acquire kinetic energy and will move from B to A. Conversely, we can say that an external force is required to keep the charge at rest or to move with uniform velocity from A to B Thus

VB – VA = WAB/q equation (2)

Often point A is taken to be at infinity , meaning a large distance from the charges that produce the electric field, and the electric potential at A is taken to be zero.

Note that the choice of zero potential at infinity is taken arbitrarily and for simplicity, such that

V = W/q equation (3)

In equation (3) V (by definition) the Work that must be done against the Electric Field to bring a test charge q from infinity to a specific location.

##### Question: 38
<span style="font-size:11.0pt;line-height:107%; font-family:&quot;Calibri&quot;,sans-serif;mso-ascii-theme-font:minor-latin;mso-fareast-font-family: Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin; mso-bidi-font-family:&quot;Times New Roman&quot;;mso-bidi-theme-font:minor-bidi; mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">What is capacitor? Define capacitance and its units.</span>
38-52

Capacitor is a device used for storing charge, it consists of two conductors separated form (without touching) each other, carrying charges of equal magnitude but opposite sign.

The basic elements of any capacitor two isolated conductors (having charge +Q and - Q) of any shape. No matter what their geometry, flat or not, we call these conductors plats, each capacitor plate carries a charge of the same magnitude, one positive and the other negative. Due to the charge the electric potential of the positive plate exceeds that of the negative plate by an amount V.

The insulating medium that separates the plates of capacitor (air or some other insulating material) is referred to as dielectric

Capacitance of capacitor:

The capacitance C of a capacitor, is the ratio of the magnitude of the charge on either conductor, is the ratio of the magnitude of the charge on either conductor to the magnitude of the potential difference between them.

When charge Q is increased on the plates of the capacitor the potential difference V also increases and vice versa

Q V or Q =CV

Where C is the constant of proportionality and is called the capacitance of a capacitor

Therefore C= Q/V eq (1)

The capacitance of capacitor is the amount of charge the capacitor can store per unit of potential difference . The capacitance of a capacitor depends upon the size and shape of the plates. Its also depends upon the separation and nature of insulating material in between the plates.

Unit of Capacitance:

The SI Unit of capacitance is coulombs per volt or the farad (F), named in honor of Micheal Fraday, such that

1F = 1C/C

The farad is a very large unit of capacitance. In practice, typical devices have capacitances ranging from microfarads 10-6 F). For practical purposes, capacitors often are labeled “µF” for microfarads and “pF” for Picofarads.

##### Question: 39
Describe how you would charge the electroscope<div><ul><li>Negatively</li><li>Positively</li></ul></div>
39-52
Electroscope can be charged by the process of electrostatic induction.
Induction of positive charge: in order to produce positive charge on the electroscope bring a negatively charged rob near the disk of electroscope. Positive charge will appear on the disk of the electroscope while negative charge will shift to the leaves. Now connect the disk of electroscope with earthed aluminum foil leaves will flow to the earth through the wire. Now if we first break the earth connection and then remove the rod the electroscope will be left with positive charge.
##### Question: 40
How we can detect the type of charge by electroscope?
40-52
Detecting the type of charge: for the detection of type of charge on a body, electroscope is first charged either positively or negatively. Suppose the electroscope is positively charged as explained before. Now in order to detect the type of charge on a body, bring the charged body near the disk of the positively charged electroscope. If the divergence of the leaves increase, the body carries positive charge . On the either hand if the divergence decreases, the body has negative charge.
##### Question: 41
How can we identify the conductors and insulators by electroscope?
41-52
Identifying conductions and insulators: electroscope can also be used to distinguish between insulators and conductors. Touch the disk of a charged electroscope with material under test. If the leaves collapse from their diverged position, the body would be a good conductor. If there is no change in the divergence of the leaves, it will show that the body under test is an insulator.
##### Question: 42
State Coulomb's law derives its mathematical formula.
42-52
Coulomb's Law: the force of attraction or repulsion between two charges is directly proportional to the product of the magnitude of charges and inversely proportional to the square of the distance between them.
Mathematically formula: Let q1 and q2 are two point charges and the distance between their centers is r.
F= kq1q2/r2
Where K is coulomb's constant.
Dependence of value of K: the value of k depends upon:
1. Medium between two charges
2. system of unit in which F, q and r are measured
3. The permittivity of free space
Value of k in air: if the medium is air between the two point charges then value of k is SI unit will be 9*109 Nm2C-2
Point charge; charge are said toe be point charges if their size are very small as compared to the distance between their center.
Note: Coulomb's law is true only for point charges whose sizes are very small.
##### Question: 43
Define electric field and explain electric intensity?
43-52
Electric field and electric field intensity: according to Coulomb's law if a unit positive charge qo is brought near a charge q placed in a space, the charge qo will experience a force. The value of this force would depend upon the distance between the two charges. If the charge qo is moved away from q this force would decrease till at a certain distance the force would practically reduce to zero.

##### Question: 44
Define electric field lines and describe its characteristics?
44-52
Electric field lines: the direction of electric field intensity in an electric field can also be represented by drawing lines. These lines are known as electric lines of force.
Direction of lines through arrow: the field lines are imaginary lines around a field charge wit an arrow head indicating the direction of force. Field lines are always directed from positive charge towards negative charge. The spacing between the field lines shows the strength of electric field.
Characteristics of electric field lines:
1. The electric field intensity is tangent to the electric field lines at each point.
2. The number of lines per unit area through a surface perpendicular to the lines is proportional to the electric field strength in a given region.
3. Electric field is strong when the field lines are close together and weak when the lines are far apart.
4. No tow field lines cross each other.
##### Question: 45
Define electrostatic potential, and also explain it
45-52
Electric potential at a point in an electric field is equal to the amount of work done in bringing a unit positive charge from infinity to that point.
Formula: If W is the work done in moving a unit positive charge from infinity to a certain point in the field, the electric potential V at this point would be given by
V= W/q
Quantity: it is a scaler quantity
Unit: its SI unit is (volt) which is equal to JC-1
Volt: if one joule of work is done against the electric field in bringing one coulomb positive charge from infinity to a point in the electric field then the potential at that point will be one volt.
##### Question: 46
What are capacitors? Describe capacitance and its units?
46-52
Capacitor: a device which is sued to store the charge for a long period is called capacitor.
Construction: it consist of two thin metal plates, parallel to each other separated by a very small distance. The medium between the two plates is air or a sheet of some insulator. This medium is known as dielectric.
##### Question: 47
Explain the characteristics of capacitors connected in parallel combinations.
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Capacitors in parallel combination: in this method the left plate of each capacitor is connected to the positive terminal of the battery by a conducting wire . In the same way, the right plate of each capacitor is connected to the negative of the battery.

##### Question: 48
Explain the characteristics of capacitor connected in series combination.
48-52
Capacitor in series combination: in this method the capacitor are connected side by side .i.e., the right plate of one capacitor is connected to the left plate of next capacitor.
##### Question: 49
Write a note on types of capacitors
49-52
Parallel plate capacitors: parallel plate capacitors are note commonly used in most devices because in order to store enough charge their size must be large which is not desirable. A parallel plate capacitor has a dielectric between its plates and is made of a flexible material that can be rolled into the shape of cylinder. In this way we can increase he area of each plate while the capacitor cab fit into small space.
Some other types of capacitor use chemical reactions to store charge like tiny batteries. These are called electrolytic capacitors.
##### Question: 50
Write a note on uses of capacitor
50-52
Uses of capacitor: they are used for tuning transmitters, receivers and transistor radios. They are also used for table fans, ceiling fans, exhaust fans, fan motors in air conditioners, cooler , motors washing machines air conditioners and many other appliances for their smooth working capacitors are also used in electronic circuit of computers etc.

##### Question: 51
Write a note on application of electrostatics.
51-52
Importance: static electricity has an important place in our everyday lives which include
• Photocopying
• Car painting
• Extracting dust from dirty carpets
• Extraction dust from chimneys of industrial machinery
##### Question: 52
Explain some Hazards of static electricity