Class 10th // Physics // Chapter - Electricity

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Chapter  - Electricity 
some important statements
1. Basically three types of particles are found in an atom.
These three particles are protons, electrons and neutrons.
2. Protons and neutrons are present in the nucleus of an atom.
3. The electron moves in orbit around the nucleus of the atom.
4. Proton has positive charge while electron has negative charge.
5. Transfer of electrons from one substance to another.    
• What is charge?
Answer: Charge is that property of a substance due to which electrical and magnetic effects arise in it.
* Charge is denoted by C / Q.
* The SI unit of charge is the coulomb.
* Charge (Q) = ne.
Where ne = number of electrons.
* 1 electron has 1.6 x 10-¹⁹ coulomb negative charge. 

Note: Charge is generated by the entry or exit of electrons in a substance.

There are two types of Charge -
1. Positive charge : The charge that arises due to the release of electrons from a substance is called positive charge.
For example: When glass is rubbed with silk, a positive charge is produced in the glass and a negative charge is generated in the silk.

2. Negative charge: The charge that is generated after the entry of an electron in a substance is called negative charge.
For example: When ebonite is rubbed with wool, negative charge is generated in ebonite.
 
Note : 
1. A substance has equal number of electrons and protons.
2. Proton has positive charge whereas electron has negative charge.
3. When an electron enters a substance, it gets negative charge and when the electron leaves it, it gets positive charge.

**
• What is called electric current?
Answer :- The rate of flow of charge flowing in a conductor is called electric current.
Electric current is denoted by "I".
The SI unit of electric current is ampere (A).
Electric current is measured with an ammeter.
Electric current (I) = charge / time
That is, I = Q / t ⇒ Q = It

• What is ampere?
Answer :- When one coulomb charge flows through a conductor in one second, then the current flowing through that conductor is called one ampere.
1 ampere = 1 coulomb / 1 charge

Note : -
1. Sometimes the value of current flowing through the conductor is very small. In this case it is measured in milli ampere (mA) or micro ampere (μA).
1 Milli ampere(mA) = 1/1000 A = 10-³ A
1 Micro ampere(μA) = 1/1000000 A = 10-⁶ A

2. Sometimes the value of current flowing through the conductor is very high. In this case it is measured in kilo ampere (kA) or mega ampere (MA).
1 kilo ampere(kA) = 1000 A = 10³ A
1 mega ampere(MA) = 1000000 A = 10⁶ A

Numerical Questions 1.
If a current of 3 ampere flows in a conductor for 2 minutes, then how many coulomb charges will flow through it?
Condition :- t = 2 minutes = 2 x 60 = 120 seconds
I = 3 A Q = ?
∵ Q = It
  ⇒ Q = 3 x 120 = 360 C

• What is electricity?
Answer: - Electricity is a type of energy, which can be easily taken from one place to another and can be converted into different forms of energy.

• What is an electric circuit?
Answer :- Electric circuit is a closed path through which electric current flows.

There are two types of electric circuit -
1. closed circuit
2. open circuit

** *
• What is electric potential?
Answer :- The amount of work done in bringing unit positive charge from infinity to a point in the electric field is called electric potential at that point.

It is often denoted by "v".
Its S.I. Unit is volt.
It is a scalar quantity.
V = W / Q
Note :-
1. The potential of the earth is assumed to be zero. But in reality it is not zero.
2. The potential of a point at infinity is zero. This is called absolute zero potential.
3. The flow of electric current is from high potential to low potential.
4. The flow of electrons is from lower potential to higher potential.

# Types of electric potential

There are two types of electric potential
1. positive electric potential
2. minus electric potential

1. Positive Electric Potential :- When a charged object is brought in contact with the earth, then the flow of electrons from the earth is towards that object, then the potential of the object is considered positive.

2. Negative Electric Potential:- When a charged object is brought in contact with the earth, then the flow of electrons is from the object towards the earth, then the potential of the object is considered negative.

• What is potential difference?
Answer :- The amount of work done in moving unit positive charge from one point to another point in the electric field is called potential difference.
{The difference between two potentials is called potential difference}
Its S.I. Unit is volt.
V = W / Q

• What is 1 volt?
Answer :- If the work done in moving 1 coulomb charge from one point to another point is one joule, then the potential difference between those two points is 1 volt.
That is, 1 Volt = 1 Joule / 1 Coulomb ⇒ 1 V = 1 W / 1 Q

Numerical Questions 2.
The work done in bringing 50 Coulomb charge from infinity to a point in the electric field is 62.5 J, then find the potential at that point.
Solution:-
∵ Q = 50 C , W = 62.5J 
⇒ V = W / Q
⇒ V = 62.5J / 50 C
⇒ V = 1.25 VOLT

• What is an ammeter?
Answer:- Such an electrical device by which the current flowing in the electric circuit is measured, it is called an ammeter.
* The ammeter is connected in series with other devices connected in the electrical circuit so that the value of the entire current of the circuit is obtained.
* It is an electrical device with a lot of resistance.

• What is a voltmeter?
Answer :- Such an electrical device by which the potential difference between any two points of the electric circuit is measured, is called a voltmeter.
* The voltmeter is connected in parallel combination with other devices connected in the electrical circuit so that the current of the circuit is greatly interrupted. Because voltmeter is a high resistance electrical device.

• Write the difference between ammeter and voltmeter:
Answer :- Following are the differences between ammeter and voltmeter. 
AmmeterVoltmeter:
1. It measures the strength of current in an electric circuit.
2. It is connected in series combination in the electric circuit. 
3. Its scale is marked in ampere. 		1. It measures the potential difference between any two points in an electrical circuit.
2. It is added in parallel combination in the electric circuit.

3. Its scale is marked in volts.
• What is resistance?
Answer: - The property of a conducting material which obstructs the flow of electric current in it is called resistance.
It is denoted by "R".
Its SI unit is Ohm (Ω).
 
Resistance = Potential Difference / Current

• What do you understand by 1 Ohm?
Answer: If there is a potential difference of one volt between the two ends of a conductor, a current of one ampere flows through it, then the resistance of that conductor is called one ohm.
1 ohm = 1 volt / 1 ampere

• On what factors does the resistance of a conductor depend?
Answer: The resistance of a conductor depends on the following factors.
1. On the nature of the conductor :- The resistance of the conductor depends on the nature of the conductor material.
As the resistance of silver is lowest, that of copper is higher, that of aluminum is higher.

2. On the length of the conductor :- The resistance of a conductor is proportional to the length of the conductor. That is, the resistance increases as the length increases and the resistance decreases as the length decreases.

3. On the area of cross-section of the conductor :- The resistance of the conductor is inversely proportional to the area of cross-section.
That is, resistance decreases with increase in thickness and resistance increases with decrease in thickness.

4. On the temperature of a conductor: - The resistance of the conductor increases as the temperature increases and the resistance of the conductor decreases as the temperature decreases.

• Write Ohm's law and give an experiment to verify it.
Answer :- The electric current flowing through a conductor at a certain temperature is proportional to the potential difference across the ends of the conductor.
That is, I ∝ V
or , V ∝ I
or , V= IR { where R is a constant }
Experiment for verification-


To verify Ohm's law, the apparatus is arranged as shown in the figure.
Action :- First of all the switch is turned on by determining the resistance by the variable resistance. Due to which electric current flows in the electric circuit. The current (I) is measured with an ammeter (A) and the potential difference (V) across the fixed resistance (R) is measured with a volt meter. The current and potential difference in the circuit are changed by changing the resistance by the variable resistance and thus five readings are taken.
Since let the current and potential difference be I1, I2, I3, I4, I5 and V1, V2, V3, V4, V5 respectively.
Now the graph is drawn by representing V with X-axis and I with Y-axis, which is a straight line. it is proved that
I ∝ V
Thus Ohm's law is verified.
Note :- 
1. If any resistances are connected in series and their equivalent resistance is R, then
R = R1 + R2 + R3 + R4 +.................
2. If any resistances are connected in parallel and their equivalent resistance is R, then  

3. If any cells are connected in series and their equivalent current is I then
Where: n = number of cells
E = electromotive force of each cell
r = internal resistance
R = external resistance 
4. If any cells are connected in parallel and their equivalent current is I then 

5. If any cells are connected in mixed order and their equivalent current is I then


Where: m = number of rows

• What is series combination of resistance? Get the recipe for equivalent resistance in this combination.
Answer:-
When several resistances are connected in such a way that one end of one resistance is connected to one end of the second resistance and the other end of the second resistance is connected to each end of the third resistance. And it is carried forward in the same manner. So this combination of resistances is called series combination of resistance.
Note: 
In series combination, equal current flows through all the resistances. But the potential difference across the ends of all resistances is different.
Derivation of expression for equivalent resistance:-

Suppose three resistances R1, R2 and R3 are connected in series as shown in the figure. In which the same current, I, flows but the potential difference at each end is different. Again assume that the equivalent resistance is R.


 • What is parallel series combination of resistance? Get the recipe for equivalent resistance in this combination.
Answer:-
When several resistances are connected in such a way that one end of them is connected to one point and the other end is connected to another point, then this combination of resistances is called parallel combination of resistances.
Note-
In this combination, the potential difference across all the resistances is the same but the current flows differently.
Derivation of expression for equivalent resistance:-

Suppose three resistances R1, R2 and R3 are connected in parallel series as shown in the figure. In which currents I1, I2 and I3 flow. But the potential difference across all three resistances is the same. Again assume that the equivalent resistance is R.

 • What is specific resistance?
Answer :- 
The specific resistance of a material is the resistance per unit length of that material.
Specific resistance is denoted by P.
P = RA / L
Where: R – resistance of the conductor
A – Area of the conductor
L – length of conductor
The unit of specific resistance is ohm/meter. 

• What is specific conductivity? 
Answer :- 
The reciprocal of the specific resistance of a conductor is called the specific conductivity of that conductor.
Specific conductivity = 1/P
Its S. I. The unit is per ohm per meter.

• How many types of substances are there in terms of their ability to conduct electric charge through themselves?
Answer :- 
From the point of view of having the ability to pass electric charge through itself, there are four types of substances.
(i) Conductor
(ii) Non conductor
(iii) Semiconductor
(iv) Superconductor

 • What is the heating effect of electric current? 
Answer : -
When electric current is passed through a conductor, that conductor gets heated. This effect of electric current is called thermal effect of electric current.
The heating effect of electric current is used in the following devices.
Electric heater, electric level, electric bulb, room heater etc.

 • Effects of elector current  :- When electric current is passed through a conductor, the effects that occur in that conductor are called the effects of electric current . 

There are three types of effects of electric current .

(i) Heating effect of electric current
 (ii) Magnatic effect of electric current.
(iii) chemical effect of electric current.

(i)  Heating effect of electric current :- 
When electric current is passed through a conductor, that conductor gets heated. This effect of electric current is called thermal effect of electric current.  

(ii) Magnetic effect of electric current :-
When electric current is passed through a conductor, a magnetic field is generated around the conductor. This effect of electric current is called magnetic effect of electric current.
Note : -
Changing the direction of electric current changes the direction of the magnetic field at the zone.
The magnetic effect of electric current is used in the following devices.
electric fan, electric motor, electric generator
(iii) Chemical effects of electric current :-
The phenomenon of completion of chemical reactions by electric current is called chemical effect of electric current.
example:- electrolysis (lysis), electroplating, electro writing 

• What is Electric Power ?
Answer : - 
 The rate of expenditure of electrical energy by an electrical device in an electrical circuit is called the electrical power of that electrical device. 
P = W / t
P = v^2 / R
P = vi
P = I^2R
The S.I. unit of electric power is watt .

• watt :-  If 1 ampere current flows at 1 volt potential difference between the ends of a conductor, then the power of that conductor is called 1 watt. 
or 
If work is being done in a circuit at the rate of 1 joule per second, then the electrical power of that circuit is called 1 watt.
 1 watt = 1v  x 1A

• What is Electric energy ?
Answer :-
 The ability to do work obtained by electric charge is called electrical energy.
Its unit is also Joule.

• kWh :- The electrical energy generated and consumed by using 1 kW of electrical power in an electrical circuit for 1 hour is called 1 kWh.
Note- 1KWh is written as 1 electric unit or unit.

• B . O . T . unit (Board of trade unit) :-  Reading the use of electrical energy from electrical meters in houses or other industrial places. O. T. It is taken only in.
1B . O . T .= -1 unit = 1kWh = 3.6x10^6 वाट

Some units :-
Electric Power = watt 
1watt = 1 volt X 1 Ampere 
  Electrical energy - major unit is kJ and Mj है
KJ = 10^3 j and1MJ = 10^6J
The unit of electrical energy is also wh.
1wh = 1watt x 1hour
1X 3600 = 3600jule
1 The practical unit of electrical energy is kWh. 
1 kWh = 1 unit = 1 B . O . T . unit = 3600000
The unit of energy, heat, work is joule.
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