This video is for UPTGT Science / UPTGT Physics Aspirants.
This video contains Unit 3 Electricity.
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This video is Part 3 and Contains following topic's Explanations.
💡OHM’S LAW:-
It states that the current I flowing through the conductor is directly proportional to the potential difference V across thee conductor, (temp. remains constant).
I "∝ " V
V "∝ "I
V "= "I R
Where, R is a constant known as Resistance of conductor.
The SI Unit of Resistance is ohm (Ω)
Dimensional Formula: [ML2T-3A-2]
💡Resistance of a conductor depends upon the following Factors:-
1. It is depend upon the nature of material and temp. of conductor.
2. It is directly proportional to the length of conductor.
R "∝ " l
3. It is inversely proportional to the cross sectional area of the conductor.
R "∝ " "1" /"A"
From eq. 1 and eq. 2: R "∝ " "l" /"A"
💡Resistivity or Specific Resistance
Resistivity is defined as the Resistance of conductor of unit length and unit cross section area.
𝝆=𝑹𝑨/𝒍
The SI Unit is ohm –meter (Ω-m)
Dimensional Formula: [ML3T-3A-2]
💡Conductance :-
It is defined as the reciprocal of resistance of a conductor. It is expressed as, 𝑮=𝟏/𝑹
The SI Unit is mho or ohm -1 (Ω-1) or Siemen (S)
Dimensional Formula: [M-1L-2T3A2]
💡Conductivity :-
It is defined as the reciprocal of resistivity of a conductor. It is expressed as, 𝝈=𝟏/𝝆
The SI Unit is mho-m -1 or Siemen per meter (Sm -1)
Dimensional Formula: [M-1L-3T3A2]
💡Electrical Energy:-
It is defined as the total work done W by the source of emf V in maintaining the electric current I in the given circuit for a specified time t.
According to Ohm's law, we have
𝑬=𝑾 = Vq = V (I t) = V I t
= I 2Rt "=" "V2" /"R" t
The SI Unit of Energy is Joule (J).
1 Joule = 1 volt x 1 Ampere x 1 Sec
💡Electrical Power:-
It is defined as the rate of electrical energy supplied per unit time to maintain the flow of electric current through a conductor.
𝑷 = V I = I 2R =𝑽𝟐/𝑹
The SI Unit of Power is Watt (W).
1 Watt = 1 Volt x 1 Ampere
1 Kilowatt (KW) = 103 W
1 Megawatt (MW) = 106 W
1 HP = 746 Watt
💡Combination of Resistors:-
1.Series Combination :-
R = "R" 𝟏 + "R2" + "R" 𝟑 +…… + "R" 𝒏
2.Parallel Combination :-
"1" /"R" = "1" /("R" 𝟏) + "1" /("R" 𝟐) + "1" /("R" 𝟑) + ... + "1" /("R" 𝒏)
💡HEATING EFFECT OF ELECTRIC CURRENT:-
When a current flow through the circuit , due to resistance heat is generated in the conductor and temp. of conductor increases. This is called Heating effect of electric current.
💡Joule’s Effect of Heating:
It states that the heat produced in the circuit is directly proportional:
Square of electric current ‘i2 ’
Resistance of wire ‘R’
Time ‘t’
Mathematically,
H = I 2Rt "=" "V2" /"R" t

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