Physics CH # 16



Definitions:
Coulomb
      It is SI unit of electric charge. One coulomb (1C) of charge being that quantity of charge which when     placed one meter from an identical charge in vacuums repels it with a force of 8.99 x 109 N.
Insulators:
      Insulators are those materials, which do not allow electric charges to pass through them. In other words,     insulators are materials that do not allow electrical current to pass. In insulators electrons are tightly     bounded to their atoms. Insulators do not have free electrons.
    Examples Plastic, rubber, wood, glass etc.
Conductor:

      Conductors are those materials, which allow electric charges to pass through them. In other words,         conductors are materials that allow electric current to pass. In conductors electrons are loosely bounded     to atoms. Conductors have free electrons.
    Examples:Copper, Gold, Aluminum, Silver etc.
Electric Field:
      Space or region surrounding a charge or charged body within which another charge experiences some     electrostatic force of attraction or repulsion when placed at a point is called Electric Field.
Electric Intensity:
      It is the strength of electric field at a point. Electric intensity at a point is defined as the force     experienced per unit positive charge at a point placed in the electric field.
    Mathematically,
E=F/q
    It is a vector quantity. It has the same direction as that of force.
 Units :    N/C or Volt/m
Electrical Potential :
      Electric potential at a point is defined as the amount of work done in moving unit positive charge against      the direction of electric field from a point to that point.

Electrical potential = work done/charge
or
U=work/q
    unit of electric potential in SI system is Volt .
                                                                        1 volt = 1 Joule/coulomb
Volt :
      Unit of electric potential and potential difference in SI system is called Volt.
It is defined as
"in an electric field potential b/w two points is 1 volt if the amount of work
done in moving 1 Coulomb charge from one point to another point is 1 Joule."
Potential Difference :
      Potential difference b/w two points A and B is equal to the amount of work done by moving a unit positive     charge from point A to point B against the electric field
   VB-VA=VAB 
or
VAB= (work)AB/q
 Unit:    Volt or Joule/Coulomb
Electric Current:
      The rate of flow of electric charge through a cross section of a conductor is called Electric Current or     Electric charge passes through a cross section of a conductor is called Electric Current.
    It is denoted by I.
Formula :
  I = Q/t
Units:
      Ampere in SI system.
      mA (milli Ampere) = 10-3A
    m A (micro Ampere) = 10-6A
Ampere :
      If one coulomb of electric charge passes through a cross section of a conductor in one second, the     amount of current passes through it is called Ampere. 1A = 1c/1sec.

Resistance:
      opposition offered by the atoms of a conductor in the flow of electric current is called Resistance. It is a     hurdle in the flow of electric current. Different substances have different resistance. Resistance of a     conductor increases with the increase in temperature.
Symbol:
      It is denoted by R.
Unit :

      Ohm  


Capacitor:
        Capacitor is an electronic device, which is used to store electric charge or electrical energy. A capacitor     stores electric charge on its plates. There are a number of types of capacitors available.

Structure Of Capacitor:
      A capacitor consists of two identical conducting plates which are placed in front of each other. One          plate of capacitor is connected to the positive terminal of power supply and the other plate is connected     to negative terminal. The plate, which is connected to positive terminal acquired positive charge, and the     other plate connected to negative terminal. Separation between the plates in very small. The space     between the plates is field with air or any suitable dielectric material

A Parallel Plate Capacitor:

Principle Of Capacitor:
      Electric charge stored between the plates of a capacitor is directly proportional to the potential     difference between the plates.     Let the potential difference between the plates is V and the charge stored on any one of the plates of     capacitor is Q then,
Q α V
Q = CV
    where
    C= Capacitance of the capacitor     For latest information , free computer courses and high impact notes

Capacitance:
      Charge storing capability of a capacitor is called capacitance of capacitor.
 Definition:
Capacitance of a capacitor is defined as the ratio of the charge stored on any of the plates of     capacitor to the potential between the plates.
Combination Of Resistors:
.     Resistance can be joined to each other by two ways:
    1. Series combination
    2. Parallel combination

Series Combination:
      Characteristics:    
   1. If different resistances are joined with each other such that there is only one path for the flow of        electric current then the combination of such resistances is called Series Combination.
    2. In series combination current through each resistor is constant.
    3. In series combination Potential difference across each resistor is different depending upon the value of         resistance.
    4. Equivalent resistance of circuit is equal to the sum of individual resistances.

Re = R1 + R2 + R3 + R4 + …………….. Rn

Disadvantage:
      If one component is fused, then the other components of circuit will not function.     For latest information , free computer courses and high impact notes visit : www.citycollegiate.com  

Equivalent Resistance In Series Combination:
      Consider three resistances R1, R2, & R3 connected in series combination with a power supply of voltage.     Potential difference of each resistor is V1, V2, & V3 respectively. Let electric current I is passing through     the circuit.     Now
V = V1 + V2 + V3
According to Ohm’s law V = IR
thus
IRe = IR1 + IR2 + IR3
IRe = I(R1 + R2 + R3)
IRe/I = R1 + R2 + R3
Re = R1 + R2 + R3
    This shows that in series combination equivalent resistance of circuit is always greater than individual     resistances.

Parallel Combination:
      Characteristics:
    1. If there are more than one path for the flow of current in a circuit then the combination of resistances     is called Parallel Combination.
    2. In parallel combination current through each resistor is different.
    3. Potential difference across each resistor is constant.
    4. Equivalent resistance of circuit is always less than either of the resistances included in the circuit.

Advantage:
      In parallel combination of resistors, if one component of circuit (resistor) is damaged then rest of the     component of the circuit will perform their work without any disturbance. It is due to the presence of     more than paths for the flow of electric current.

Equivalent Resistance In Parallel Combination:
      Consider three resistances R1 , R2 & R3 connected in parallel combination with a power supply of voltage     V.     Now
I = I1 + I2 + I3
    according to Ohm’s law
V/R = I
Therefore,
V/Re = V/R1 + V/R2 + V/R3
V/Re = V(1/R1 + 1/R2 + 1/R3)
V/ReV = 1/R1 + 1/R2 + 1/R3
OR
1/R=1/R1 + 1/R2 + 1/R3

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