Electricity Class 10 - Science notes

Electricity Class 10 - Science Ncert notes

Charge:

The physical property which determine the deficit or excess of electrons in body is called charge.
charge is an intrinsic property of matter.
Its SI unit is coulomb.
It is scalar quantity.

Type of Charge:

Positive Charge:

The charge on body due to deficit of electrons is called positive charge. and body is called positively charged body.

Negative Charge:

The charge on body due to excess of electrons is called negative charge. and body is called negatively charged body.

Properties of Charge:

A stationary charge produces electric field around it.
A moving charge produces magnetic field around it motion.
Like charges exert repulsion force to each other.
Unlike charges exert attraction force to each other.
Charge is quantized in nature. i.e value of charge never lie between ( n-1 ). e and n.e. where ‘n’ is integer and ‘e’ is charge on electron.
Charge is conservative . this is because it is scalar quantity.

Q. Define +1 Coulomb:

Ans:

If two equal positively charged body are kept in air at 1 m distance and they exert force of 9 x 10⁹ N to each other , then amount of charge on each body will be +1 C.

OR,

If a body has deficit of 6.25 x 10¹⁸ electrons, then charge on body will be +1 C.

Q. Define -1 Coulomb:

Ans:

If two equal negatively charged body are kept in air at 1 m distance and they exert force of 9 x 10⁹ N to each other , then amount of charge on both body will be -1 C.

OR,

If a body has excess of 6.25 x 10¹⁸ electrons, then charge on body will be +1 C.

Calculate Amount of charge on body:

If a body has deficit of ‘n ‘ electrons, Then charge on body , Q = + ne C

If a body has excess of ‘n ‘ electrons,Then charge on body , Q = - ne C

+ve sign show deficit of electrons in body.
-ve sign show excess of electrons in body.

Calculate Number of deficit or excess electrons : (n)

n= Q / e

or, n= 6.25 x 10¹⁸ x Q

Electricity:

The flow of free electrons ( charge) in conductor is called electricity.

Electric Current:

Amount of charge passing through any cross sectional area of conductor in one second is called electric current.

In time ‘t’ second, flowing charge = Q

In time 1 second , charge = Q / t

i.e i = Q / t

in other words,

the rate at which electricity passes through any cross sectional area of conductor is called electric current.

Properties of electric current:

It is scalar quantity.
Current is measured by ammeter and galvanometer .
Its SI unit is ampere.
Conventional direction of electric current is opposite direction of electron’s motion.
In circuit , direction of current is taken from positive terminal of battery.

Q. Define 1 ampere .

Ans:

We know that , I = Q / t

If Q = 1 C and t = 1 sec.

Then, I = 1 C / 1 s = 1 A

When 1 coulomb charge passes through any cross section of conductor in one second , then current in conductor will be 1 ampere.

Mechanism of electric current:

When voltage is applied across conductor , the free electrons from one end ‘A’ of conductor begin to move towards positive terminal of battery due to attraction.

Hence end ‘A’ becomes positive.

Free electrons near the end ‘A’ move towards it to neutralize .

There occur deficit of electrons at other end ‘B’ of conductor.

The end ‘B’ attract electrons from negative terminal of battery.

Thus flow of electrons is maintained from negative terminal to positive terminal.

Direction of conventional current is taken opposite direction of electron’s motion. So direction of current is positive to negative.

Electric Potential

Electric potential at any point in electric field is defined as -

Energy of 1 coulomb charge at any point in circuit is called electric potential at that point.

* If charge q consist amount of energy W joule at point at Point ‘P’

Then energy per coulomb charge = W / q

So , Electric potential at point ‘P ‘ V = W / Q

Potential Difference

* When electrons move from low potential to high potential then it release energy .

* Amount of energy released by 1 C electrons when it passes from one point to another point is called potential energy.

Let charge (- Q ) passes from Lower potential ( point A ) to Higher potential ( Point B ) in electric circuit and it release W joule energy .

Then potential difference b/w both point

V_B - V_A = W / Q

Properties:

Its SI unit is Volt.

It is a scalar quantity.

Positive test charge always move from high potential to low potential.

Negative test charge always move from low potential to high potential.

Thus electric current always flow from high potential to low potential.

Electro motive force ( E.M.F ) :

Energy given by battery to each coulomb charge to flow in circuit is called e.m.f of battery.

e.g. if a battery supplies 4 J energy to each coulomb, it means emf of battery is 4 V.

Resistance:

The opposition offered by a conductor to the flow of free electrons is called resistance.

Resistance is also called electric friction.

Its SI unit is ohm ( Ω )

Factors on which resistance depend :

Resistance of conductor depends on following factors.

It is directly proportional to length of conductor.

i.e R α L

it is inversely proportional to cross sectional area of conductor.

i.e R α 1 / A

it depends on nature of conductor.

It depends on temperature of conductor.

Derive resistance formula: R = ρ . L / A

At constant temperature and for same material, resistance depend on only two factors.

It is directly proportional to length of conductor.

i.e R α L ---(1)

it is inversely proportional to cross sectional area of conductor.

i.e R α 1 / A ----- (2)

combine (1) and (2)

R α L / A

i.e , R = ρ . L / A

where , ρ is constant and known as specific resistance or resistivity of materal.

Specific resistance :

We have , R = ρ . L / A

When L= 1 m, A= 1 m²

Then , R = ρ

Thus, resistance of conductor having length 1 m and area of cross section 1 m² is known as resistivity.

Or,

Resistance between opposite face of cubic material having dimension 1 m is called resistivity.

It depends on nature of material and its temperature.
Resistivity increases on increasing with temperature.
It does not depend on shape and size of material.
Its unit is Ω-m .

Ohm’s law:

At constant temperature and same physical condition, Current flowing through the conductor is directly proportional to the voltage applied across it .

i.e I α V

or, V α I

V = IR

Where , R is constant and called resistance of conductor.

Its SI unit is V / A or Ohm .

I - V graph: ( For Conductor )

Graph drawn between current and voltage is straight line . it is because the ratio of voltage and current is always consatant.

i.e. V / I = R

Here , R is slope of graph and R = tanθ, Where, θ is angle of inclination .

Define 1 ohm :

Resistance of conductor through which 1 A current flow when 1 V is applied across it is called 1 ohm.

Sunday, August 21, 2022