10th Physics Electricity notes

 CLASS 10th 

ICSE/ CBSE Notes-By Er. Amit Singh

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ELECTRICITY

• Electricity, phenomenon associated with moving electric charges.
•  Electric charge is a fundamental property of matter.
• The unit of electric charge in the M.K.S. and SI systems is the coulomb 
•  In electricity the particle involved is the electron.
• Electric charges are of two  types, 

1. positive  charge
2. Negative charge

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Positive charge

• A positive charge occurs when the number of protons exceeds the number of electrons.
•  A positive charge may be created by adding protons to an atom or object with a neutral charge.
•  A positive charge also can be created by removing electrons from a neutrally charged object
• When an object has a positive charge it means that it has more protons than electrons.

Negative charge

• When an object has a negative charge it means that it has more electrons than protons.
• A negative charge is an electrical property of a particle at the subatomic scale.
•  An object is negatively charged if it has an excess of electrons.

Properties of charge

Electricity

• 1-Like charges repel while unlike charges attract each other.
• 2-Charge is a scalar.
• 3-Charge is transferable: When a charged body is put in contact with an uncharged body, the uncharged body becomes charged due to transfer of electrons from one body to the other.

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q1/q2 charges	Force on q1 charge	Force on q2 charge
- / -	←⊝	⊝→	repletion
+ / +	←⊕	⊕→	repletion
- / +	⊝→	←⊕	attraction
+ / -	⊕→	←⊝	attract

Coulomb unit

The electric charge is measured with the unit of Coulomb [C].

One coulomb has the charge of 6.242×10¹⁸ electrons:

1C = 6.242×10¹⁸ e

Electric Charge = Number of electron x  e

Q = n e

Particle	Charge (C)	Charge (e)
Electron	1.602×10-19 C	-e
Proton	1.602×10-19 C	+e
Neutron	0 C	0

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Electric circuits

• The electric circuits are closed-loop or path which forms a network of electrical components, where electrons are able to flow.
•  This path is made using electrical wires and is powered by a source, like a battery. 
• The start of the point from where the electrons start flowing is called the source
• you would need the following,
• Electric bulb
• Wire
• Electrical tape
• A battery etc

Important symbols used in Electric circuit

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Electric Circuit Formula

Following are the list of formulas that are used in electric circuits:

Quantity	Formula	Notations
Electric current	$I=\frac{Q}{t}$	I is the current Q is the charge flowing t is the time period
Resistance	$R=\rho .\frac{L}{A}$	R is the resistance ρ is the resistivity value of the wire L is the length of the wire A is the cross-sectional area
Voltage	$\Delta V=I.R$	ΔV is the electric potential difference
Power	$P=\frac{\Delta E}{t}$	P is the power ΔE is the energy gain or loss t is the time period
Series circuit	$R_{eq}=R_1+R_2+R_3+\dots$	Req is the total resistance of the resistors placed in series R1, R2… are the resistors placed in series
Parallel circuit	$\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+\dots$	Req is the total resistance of the resistors placed in parallel R1, R2… are the resistors placed in parallel

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Electric current

• An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space.
•  It is measured as the net rate of flow of electric charge through a surface

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• The SI unit of electric current is the ampere, or amp, The ampere (symbol: A).
•  which is the flow of electric charge across a surface at the rate of one coulomb per second.
• Electric current is measured using a device called an ammeter

Electric Potential

• Electric potential is defined as the amount of energy to move a unit of electric charge from one point to another point.
• It is also called electric field potential.
• Electric potential at infinity is assumed to be zero.
• Electric potential V = W/Q
• Unit of electric potential is  VOLT

1 volt = 1 joule / 1 coulomb

Potential difference

• Moving of electron  take place when the potential difference occur between two points. it means there is a difference  of electric pressure between two point is called potential difference.
• The SI Unit of potential difference is VOLT.
• 1 volt  is equal to 1 joule per coulomb.

RESISTANCE 

• Resistance of the wire is directly proportional to the length of the wire   

• R ∝ L 

• Resistance of the wire is inversely proportional to the cross sectional area of the wire.

• R  ∝ 1/A
• if  R ∝ L  ,R ∝ 1/A   ,then R ∝ L/A  , R = σ L/ A 

            Where  σ = Resistivity of the Wire

• If length of the wire is double then resistance will be also doubled

• If length of the wire is half then resistance will be also halved.

• If the cross sectional area of the wire is double then the resistance of the wire will be halved

• If the cross sectional area of the wire is half then resistance of the wire will be doubled.   

• If the diameter of the wire is double then the resistance of that wire will be one fourth.

• If the diameter of the wire is half then the resistance of that wire will be four times       

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combination of  Resistance

• There are mainly two types of combination  in resistance

1. Series Combination
2. Parallel Combination

one more combination  mix combination in  which both series and parallel combination  are used.

Series Combination

   R =  R1 +R2 +R3

• In series combination two or more resistance are connected end two end 

• In series combination second  end of the first resistance is connect to the first end of the second resistance.

• In series combination current is same in each  resistances.

• In series combination voltage is different in each resistances.

Parallel combination

1/R = 1/R1 + 1/R2 + 1/R3

• In parallel combination one end of each resistance is connected with one point  and other end of each resistance is connected with other point. 

• In parallel combination each  resistance  have same voltage.

• In parallel combination each resistance have different current.

• In case of parallel combination the resultant resistance will be less than either of the individual resistances.

• If a wire has resistance R is cut in  two equal parts, then each parts of the wire  having resistance  half   ie. R/2 

• Lights in our houses are wired in parallel combination.

• Each electrical appliance have same voltage in parallel combination.

Electric Power

• work done per unit time is called electric power, power is denoted by 'p'

• Electric Power = work done /time  taken

• P = W/T

• SI unit of Power is watt.

• Electric Power is also defined as the electrical energy consumed per unit time

• Power = Electrical Energy / Time

• P = E/T
• When one joule energy is used for one second then electrical power is equal to one watt