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Download 10th Class Physics Notes (Unit # 13) for Federal Board (FBISE) Islamabad

Download 10th Class Physics Notes (Unit # 13) for Federal Board (FBISE) Islamabad

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Download 10th Class Physics Notes (Unit # 13) for Federal Board (FBISE) Islamabad


How can you show by simple experiment that there are two types of electric charges?
·        Take a plastic rod rubbed with fur and suspended horizontally.
·        Bring another plastic rod already rubbed with fur close to the suspended rod.
·        The suspended rods show repulsion. It means during rubbing they get same kind of charges.
·        Now take a glass rod which is rubbed with silk.
·        It is brought near another plastic rod (already rubbed with fur) and suspended.
·        It also shows attraction.
·        These two experiments confirm the presence of two

What is the method of charging bodies by electrostatic induction?
The process of charging an insulated conductor develops positive charge at one end and negative charge at the other end in the presence of a charged body is called electrostatic induction.

How does electrostatic induction differ from charging by friction?
·        In case of electrostatic induction the body is not physically in contact with the other body to be charged.
·        The charged body is brought near to the body to be charged.
·        But in case of friction the surfaces of the two bodies are rubbed with each other, so there is mutual transfer of electrons.

What is gold leaf electroscope? Discuss as working principle with a label diagram.
An electroscope is an instrument used for detecting and testing the nature of charge on a body. One special type of electroscope is gold leaf electroscope.
Description: scan0001        Description: scan0001        Description: scan0001
Construction / Structure: -
i)            It consists of a brass rod which has a brass disc connected to its upper end.
ii)           Two very thin gold leaves are attached to its lower end.
iii)         By the help of cork this assembly is mounted inside a glass jar with a brass disc projected outside.
iv)         A thin foil of aluminium is pasted in the inner surface of jar.
Use/Working of Electroscope: -
i)            First of all electroscope will have to be charged with +ev or –eve charge.
ii)           In order to charge the electroscope positively, touch the disc with positively charged body and vice versa. 
iii)         In order to detect the presence of charge on a body bring it near the disc.
iv)         If the divergence of leaves increases then the body has the same kind of charge as the electroscope carrying.
v)           If the divergence of leaves decreases then the body has the opposite charge as the electroscope carrying.

Suppose you have a glass rod which becomes positively charged when you rub it with wool. Describe, how would you charge the electroscope i) negatively ii) positively?
·        In order to produce positive charge on the electroscope, bring a negative charged rod near the disk of the electroscope.
·        Positive charge will appear on the disk and negative chares will shift to the leaves.
·        Now connect the disk of electroscope to the earthed aluminum foil by connecting wires.
·        Charges of the leaves will flow to the earth through the wire.
·        Now if we first break the earth connections and then remove the nod the electroscope will be left with positive charges.
·        Similarly we can charge it negatively by using positively charged rod.

With the help of electroscope how you can find presence of charge on a body?
·        If a neutral rod is brought near the disk of electroscope, there is no deflection on the leaves of the electroscope.
·        When a positively or negatively charged rod is brought near the disk of electroscope then in either case the gold leaves diverge or distance between the two increases.

Describe how you would determine the nature of the charge on a body by using electroscope.
·        We take a charged electroscope. The sign of charge positive or negative on its leaves is already known. Consider the electroscope is positively charged.
·        Now a charged body is brought near the disk of the positively charged electroscope.
·        If the divergence of the leaves increases then the body carries positive.
·        On the other hand if the divergence decreases then the body carries negative charge.

What is meant by electric field and electric intensity?
·        An electric field is the region around any electric charge q within which it can exert coulumb’s force on any other electric charge when placed in it.
·        The strength of electric field at any point in space is known as electric field intensity. It is represented by E.
Explain Coulomb’s law of electrostatic and write its mathematical form?
  • It states that the force of attraction or repulsion between two charges is directly proportional to product of the magnitudes of the point charges.
        Mathematically   F      α       q1q2
  • And this force is inversely proportional to the square to the distance between these two charges.
        Mathematically   F       α       1/r2

        Combining these two facts we get
                                 F      α       q1q2/r2

                                 F      =       k --------
  • The constant of proportionally K depends upon the nature of medium between the two point charges

Is electric intensity a vector Quantity? What will be its direction?
Electric intensity is a vector quantity.lts direction is the same as the direction of Coulomb’s force.

Find the electric intensity due to a point charge q?
Consider a charge q is placed at a point, it is called field charge and a unit positive charge qo experiences a force F when placed inside electric field of charge q.
The force experienced by unit charge is =      F / qo
It is also known as value of electric field intensity   E      =       -----

How would you define potential difference between two points? Define its unit.
Electric potential at a point in 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.
One Volt:
The electric potential is said to be one volt, if one joule work work is done in brining a one coulomb positive charge.

Show that the difference can be described as energy transfer per unit charge between the two paints.
If W is the amount of work done in moving a charge q from infinity to a certain point against in the field. So that W/q = work done on unit charge.
It is converted into P.E. The electric potential is denoted by symbol V where V =W/q

This shows that “electric potential is equal to electric potential energy per unit charge.
It is scalar quantity. Its SI unit is JC-1. It is called Volt.
Describe capacitor as an energy staring device?
We define capacitor is a charge storing device but in actual it is energy storing device. In order to store the charge on a capacitor work is to be done, due to which electric potential is changed. So that energy is stored in the capacitor. The formula for the energy stored in a capacitor is given as E = ½ CV2
Where C is the capacitance and V is the potential difference.

What do you mean by the capacitance of a capacitor? Define units of capacitance.
Capacitance of capacitor is the ability to store the charge. By the capacitor equation:
Q      =      CV,           or     C      =      Q/V
SI Unit of capacitance is “farad”. One farad is the capacitance of that capacitor which can store an electric charge of one coulomb when the potential difference applied across the capacitor is one volt.

Derive the formula for the effective capacitance for a series combination of a number of capacitors.
  • Each capacitor has the same charge across it.
Q = Q1 = Q2 = Q3
  • The potential difference across each capacitor is different due to different values of the capacitances.
  • The voltage V of the battery has been divided among the capacitors, we can write
V = V1 + V2 + V3 ………………………………… (1)
  • The equations for three capacitors are
Q = C1V1            =              V1     =      Q/C1
Q = C2V2            =              V2     =      Q/C2
Q = C3V3            =              V3     =      Q/C3
  • Adding the above equations, we get
V      =      V1 + V2 + V3
V      =      Q/C1 + Q/C2 + Q/C3
V      =      Q(1/C1 + 1/C2 + 1/C3)
  • The equation for the single equivalent capacitor is
Q = CeqV    =      V      =      Q/Ceq
  • Putting value of V in equation (1)
Q/Ceq = Q(1/C1 + 1/C2 + 1/C3)

1/Ceq = 1/C1 + 1/C2 + 1/C3

Discuss different types of capacitors.
Paper Capacitor:
  • Paper capacitor is an example of fixed capacitors.
  • The paper capacitor has a cylindrical shape.
  • Usually an oiled or greased paper or a thin plastic sheet is used as dielectric medium between the two aluminum foils.
  • The paper or plastic sheet is firmly rolled in the form of cylinder and then it is closed into a plastic case.
Mica Capacitor:
  • It is another example of fixed capacitor.
  • In such kind of capacitor mica is used as dielectric between the two metal plates.
  • Wires are projected out of the case for making connections.
  • If the capacitance is to be increased large numbers of plates are piled up, one over the other.
Electrolyte Capacitor:
  • Such capacitor is used to large amount of charge at relatively low voltage.
  • It consists of a metal foil in contact with an electrolyte solution that conducts charge by virtue of the motion of the ions contained in it.
  • When voltage is applied between the foil and the solution, a thin layer of metal oxide (an insulator) is formed on the foil, thus this layer serves as the dielectric

What is difference between variable and fixed type capacitor?
Fixed Capacitor:
The capacitor having the fixed capacitance. It is due to its constant area of storing the charge is called fixed Capacitor. For example paper and mica are fixed capacitors.
Variable capacitor:
In variable capacitors some arrangement is made to change the area of the plates facing each other.

Enlist some uses of capacitors.
Capacitors are widely used in electrical and electronic circuits. For example:
  • They are used in tuning circuits of T.V. and radio in electric motors/fans etc.
  • They are used in electronic circuits of computers etc.
  • They are used to differentiate between high frequency and low frequency signals. They in used as filters in the circuits of rectifiers.
  • The ceramic capacitors are true durable and an: superiors in their use.

Discuss one application of static electricity.
Static electricity has wide application in our daily life like photocopying, car painting and extracting dust from dirty capes and from chimneys of industrial machinery. One of them is give below.
Electrostatic Air Cleaner:
·        An electrostatic air cleaner is used in homes to relieve the discomfort of allergy suffers.
·        Air is mixed with dust and pollen enters the device names positively charged mesh semen.
·        The airborne particles become positively charged when they make contact with the screen.
·        Then they pass through a second negatively charged mesh screen.
·        The electrostatic force of attraction between the positively charged particles in the air and negatively charged screen causes the particles to precipitate outer the mm of the screen.
·        Through this process we can removes a very high percentage of contaminants from the air stream.

What are hazards of static electricity?
·        The phenomenon of lightening occurs due to a large quantity of electric chare build up in the heavy thunderclouds.
·        The thunderclouds are charged by friction between the water molecules in the thunderclouds and the air molecules.
·        When the charge on the thunderclouds is sufficiently high.
·        It can produce positive and negative charges in the air.
·        The huge amount of negative charge is discharged to the highest object and on the ground and can harm them.
·        That is why it is dangerous to swim in the open sea, play in an open ground during a thunderstorm.
·        To prevent the tall building from damaging, lightening conductors are used.
·        The purpose of this conductor is to provide discharge path to flow charges from air top of building to earth.
Fires or Explosions:
·        A fire or explosion may occur due to excessive build-up of electric charge produced by friction.
·        In case of fuel carrier (gasoline/petrol) truck gets charge through tires due to friction.
·        This excess of charge can cause fire or explosion.
·        To avoid such accident a conducting chain is suspended from the truck touching road.
·        So the excess of charge flow to earth from the body of the truck.
·        In case of aero plane, it gets charge on it due to air friction.
·        There are quenching machines in the aero plane which neutralize the body of aero plane constantly.
·        When the plane lands it is earthed to cause the flow of excess of charges to earth.

An electrified rod attracts pieces of paper. After a while these pieces fly away. Why?
When an electrified rod brings close to a piece of paper, opposite electric charges appear on piece of paper due to electrostatic induction. After attraction the positive charge body attracts the electrons from other so become neutral. Force finishes and paper flies away.



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Download Class Notes: Download 10th Class Physics Notes (Unit # 13) for Federal Board (FBISE) Islamabad
Download 10th Class Physics Notes (Unit # 13) for Federal Board (FBISE) Islamabad
Download 10th Class Physics Notes (Unit # 13) for Federal Board (FBISE) Islamabad
Download Class Notes
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