The chapter

**E****lectricity**in class**X PHYSICS**covers the topics like electric charges, electric current,electric potential,ohm's law, resistances ,electric power and electric energy. Here we are going to provide**Important definitions and short notes**of each topic and a**sheet of questions for practice**which would cover each and every topic of the chapter.**ELECTRICITY - IMPORTANT DEFINITIONS**

__Current-__Rate of flow of charge is called Current.S.I. unit of electric current is Ampere. Conventionally, direction of current is opposite to the direction of flow of electrons.

**I = Q / t**

__One Ampere__- The current is said to be 1 ampere when one coulomb of charge is passed per second through a conductor.

__Ammeter__- It is the device used to measure electric current in the electric circuit. It is always connected in series in the circuit.

__E__**- a closed path of electric current is called electric circuit.**

__lectric circuit__**It is defined as the work done to move a unit charge from one point to another. Its S.I. unit is volt (V).**

__Potential difference -__**Potential difference (V) = work done(W) / charge(Q)**

**1 volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move the charge of 1 coulomb from one point to another.**

__One Volt -__**1 V = 1 J/C**

**It is a device used to measure potential difference. It is always connected in parallel across the points between which the potential difference is to be measured.**

__Voltmeter -__**It is a device used to detect current in the circuit. It is always connected in series.**

__Galvanometer -__**It states that**

__Ohm's law -__**“ the potential difference across the conductor is directly proportional to the electric current, provided physical conditions( temperature, pressure etc) remains same.**

**V ∝ I**

**V = I R , where R is proportionality constant called Resistance**.

**It is the property of a conductor to resist the flow of charges through it. Its S.I. unit is Ohm(Ω).**

__Resistance -__**- The resistance of a conductor is 1 Ohm if 1 ampere current is passed across the two ends of conductor having potential difference 1 volt.**

__One Ohm__**Factors on which resistance of conductor depends-**

(i) Resistance is directly proportional to the length of the wire .

**R∝ l**
(ii) Resistance is inversely proportional to the area of cross section i.e. a thin wire will have more resistance then a thick wire.

**R ∝ A**
(iii) When we increase the temperature, resistance of conductor increases.

**R ∝ l/A**

**R = ρ l / A**

**Where ρ is called resistivity or specefic resistance of material.**

**- It is defined as the resistance of a wire having length 1 m and area of cross section 1 m 2. S.I. unit of resistivity is Ω m.**

__Resistivity__

__Combination of Resistors:__**If two or more resistors are connected in series combination,equivalent resistance of combination -**

__(i) Series Combination -__**R = R 1 + R2 + R3 ……**

**If two or more resistors are connected in parallel combination, equivalent resistance of combination -**

__(ii) Parallel Combination -__**R = 1/R1 + 1/R2 + 1/R3 …….**

**- It states that heat produced in a resistor is -**

__Joule’s law of heating__
(i) directly proportional to the square of current

(ii) directly proportional to resistance

(iii) directly proportional to time for which current flows through a resistor.

**H = I2Rt**

__Practical applications of heating effect of current -__- In bulb, heating effect of current in filament produces light.
- Fuse in electric circuit is most important application of heating effect it protects circuit from over voltage and high current.
- The electric iron, electric toaster, electric kettle, electric heater all are based on heating effect of current.

**The rate of doing work is called power. s i unit of power is watt (W).**

__Electric power -__**P = V x I**

**P = V x (V/R) = V2 / R**

**P = (IR) x I = I2 R**

**- It is the power consumed by a device that carries 1 A of current when operated at potential difference of 1 V.**

__Watt__**Commercial unit of electrical energy is kilowatt hour (KWh).**

__Commercial unit of Electrical Energy -__
1 KWh = 1 KW x 1 hour

1 KWh = 1000 W x 3600 seconds

1 KWh = 3.6 x 106 J

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