Class 10 Electricity Notes
Notes Previous Years Questions Important QuestionsElectricity Notes
Charge(Q):-
Electric charge is the basic physical property of matter that causes it to experience a force when kept in an electric or magnetic field.
- It can be positive or negative.
- S.I. unit – Coulomb (C)
Quantisation of Charge:-
Every charge is an integral multiple of a basic charge i.e., charge on an electron(e^{–}).
- Q=ne
- Number of electrons(n) = Q/e
- Charge on an electron (1e^{–}) =1.6 x 10^{-19} C
Electric Circuit:-
A continuous and closed path of an electric current is called an electric circuit.
Electric current(I):-
The rate of flow of electric charge is called electric current.
- I = Q/t
- S.I. unit:- Ampere(A)
- Conventionally, the direction of flow of electric current is opposite to the direction of flow of electrons
- The amount of electric current in a circuit is measured by an instrument called ammeter.
- An ammeter is always connected in series in a circuit.
- 1 mA = 10^{-3} A & 1 µA = 10^{-6} A
1 Ampere:- The electric current flowing through a circuit is said to be 1 ampere when 1 coulomb of charge flows through it per second.
Electric Potential:-
The work done to move a unit charge from infinity to a point is known as electric potential of that point.
Electric Potential Difference:-
The work done to move a unit charge from one point to another point is called potential difference between the two points.
- V = W/Q
- S.I. unit:- Volt(V)
- Potential difference is measured by an instrument called voltmeter.
- Voltmeter is always connected in parallel across the points between which the potential difference is to be measured.
1 Volt:- The potential difference across the two points of a conductor is said to be 1 volt when 1 joule of work is done to move a charge of 1 coulomb from one point to the other.
Ohm’s Law:-
At constant temperature, the potential difference across the ends of a conductor is directly proportional to the amount of current flowing through it.
Mathematically,
V ∝ I
V = IR where, R is constant of proportionality & is known as resistance.
Circuit diagram and V-I graph for Ohm’s law:-
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Resistance:-
The property of a conductor to oppose the flow of charges through it is called resistance.
- R = V/I
- S.I. unit:- Ohm (Ω)
1 Ohm:- The resistance of a conductor is said to be 1 Ω if the potential difference across the ends of a conductor is 1 V and the current flowing through it is 1 A.
Resistor:- A conductor having some appreciable resistance
Variable Resistance/Rheostat:- A component used to regulate current without changing the voltage source
Factors on which resistance of a conductor depends are:-
- its length (l)
- its cross-section area (A)
- nature of its material
Mathematically,
R ∝ l ——–(i)
R ∝ 1/A ——(ii)
On combining (i) & (ii):-
R = ρl / A where, ρ(rho) is constant of proportionality & is known as resistivity
Resistivity/Specific Resistance(ρ):-
The resistance of the conductor of unit length & unit area of cross section is called its resistivity.
- ρ =RA/l
- S.I. unit :- ohm meter (Ω m)
➢ On increasing the temperature, both resistance and resistivity of a conductor increases.
Resistors in Series:-
When two or more resistors are connected end to end to each other, then they are said to be connected in series.
In series combination,
- current flowing is same through each resistor.
- the potential difference across each resistor is different.
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Consider current ‘I’ is flowing through the circuit & the potential difference across resistors R_{1}, R_{2} & R_{3} be V_{1}, V_{2}, V_{3} respectively. Let the total potential difference be ‘V’ & equivalent resistance be ‘R_{s}‘.
On applying Ohm’s law,
V = IR_{s} ; V_{1} = IR_{1}; V_{2} = IR_{2} ; V_{3} = IR_{3}
Now, V = V_{1} + V_{2} + V_{3}
or, IR_{s} = IR_{1} + IR_{2} + IR_{3}
or, R_{s} = R_{1} + R_{2} + R_{3}
Resistors In Parallel:-
When two or more resistors are connected together between two points then they are said to be connected in parallel.
In parallel combination,
- The potential difference is same across each resistor.
- The current flowing through each resistor is different.
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Consider potential difference across the resistors be V & the current flowing through resistors R_{1}, R_{2} & R_{3} be I_{1}, I_{2} & I_{3} respectively. Let the total current flowing through the circuit be I & equivalent resistance be R_{p}.
By Ohm’s law,
I = V/R_{p} ; I_{1} = V/R_{1} ; I_{2} = V/R_{2} ; I_{3} = V/R_{3}
Now, I = I_{1} + I_{2} + I_{3}
or , V/R_{p} = V/R_{1} + V/R_{2} + V/R_{3}
or , 1/R_{p} = 1/R_{1} + 1/R_{2} + 1/R_{3}
Advantages of parallel combination over series combination:-
- In series combination, current remains same throughout the circuit while in parallel combination, current is different through each device and different components require different currents to operate properly.
- If one device fails in series circuit then none of the devices works while it will not happen in parallel circuit.
- The total resistance in a parallel circuit is decreased while the total resistance in series circuit is increased.
Electric Power:-
The amount of electrical energy consumed per unit time in an electric circuit is known as electric power.
P = W/t
Or, P = VQ/t
Or, P = VI = I^{2}R = V^{2}/R
- S.I. unit of power:- Watt(W)
1 Watt:- Electric power of an appliance is said to be 1 W if 1 A of current flows through it and the potential difference across its ends is 1 V.
Heating Effect of Electric Current:-
W = VQ =VIt
or H = VIt = I^{2}Rt
Joule’s Law of Heating:-
According to Joule’s law of heating, heat produced in a resistor is directly proportional to
- square of current (H ∝ I^{2})
- resistance (H ∝ R)
- time for which current flows (H ∝ t)
H = I^{2}Rt
- S.I. unit of energy:- Joule(J)
- Commercial unit of energy:- kilowatt hour(kW h)
Practical Applications of Heating Effect of Electric Current:-
Appliances based on heating effect of electric current are electric bulb, electric iron, electric toaster, electric oven, electric kettle, electric heater, fuse etc.
- Tungsten is used as the filament of the electric bulb.
- The bulbs are filled with chemically inactive gases like nitrogen and argon to prolong the life of the filament.
Conversion of Commercial Unit of Energy to S.I. Unit:-
1 kW h = 1000 W x 3600 s = 3.6 x 10^{6} Ws = 3.6 x 10^{6} J
1 unit = 1 kW h = 3.6 x 10^{6} J
Comments
Saurabh singh
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Vikash Kumar
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Vinit Anand
What is the direction of electric current?
Kajal
Opposite to the direction of flow of electrons.
BLACK1SEVEN
Positive to negative
Herb Zmiejko
Yes, this is a Good one
Luna Manto
plant of API
Mughal Thakur
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I really like it.