Electricity Class 10th notes

Electricity Class 10th notes part 1

INTRODUCTION

Electricity is an important source of energy. Today 90% work of human life is carried out by help of electricity. Whole industry and transport system is based on the electricity.

Types of electricity

Static electricity: Electricity in which charges remain in rest due to absence of free electrons such as in insulator body (in which electric effect can be experienced but cannot be transmitted from one to another point). In insulator body if we want to create charge at any point than by friction method, we can do this.

Current electricity: In current electricity charges remains in motion due to the presence of free electrons such as a metallic wire.

Electric potential

Electric potential defined as the amount of work done in bringing the unit + ve charge from infinity to a point in an electric field.

Electric potential difference

Electric potential difference or potential difference defined as the amount of work done in moving a unit +ve charge from one point to another point in an electric circuit.

Potential difference = work done / quantity of charge

                                                            V =W / Q

• Here V is the potential difference, W is the work done, Q is the quantity of charge
• S.I. unit of V is volt, W is joule & Q is coulomb.
• Define one VOLT = Potential difference is said to be one volt if one joule of work is done in moving one coulomb of charge from one point to another point.
• 1volt = 1joule / 1coulomb
• Potential difference is measured by Voltmeter. It has high value of resistance due to this voltmeter connect in parallel.

ELECTRIC CURRENT

Electric current is a flow of charge in a conductor body such as in metallic wire.

                                             Current = charge / time

                                                          I = Q / T

• Here I is current, Q is charge and T is time.
• S.I. unit of current is Ampere, charge is coulomb and of time is second.
• Define one AMPERE = Current is said to be one ampere when one coulomb of charge flow in one second.
• 1Ampere = 1C / 1Second
• Current is measured by the Ammeter that has low resistance.
• Ammeter is always connecting in the series.
• 1mA = 10-6A , 1mA = 10-3A
• Direction of electric current or conventional current is from +ve to –ve terminal.
• Direction of free electron is –ve to +ve terminal.
• Direction remains random in absence of E.M.F.

SYMBOLES THAT USED IN ELECTRICITY

Closed key meaning is to flow of current in circuit while open key means that no flow of electron.

OHM’S LAW

According to ohm’s law at constant temperature, current flow through the conductor is directly proportional to the potential difference across its ends. Ohm’s law gives relation between current and potential difference.

                                                                 I α V

                                                                V α I

                                                               V = IR

Here R is the resistance of conductor. Values of resistance depend on four factors:

1. Length of conductor.
2. Area of cross section.
3. Nature of material.
4. Temperature of conductor. NOTE: resistance of all pure metal increases with the rise of temperature and decrease with the lowering of temperature. Define one ohm: one ohm is that value of resistance when potential difference of one volt is applied to its end and current of one ampere flow through it.
5. 1ohm = 1volt / 1amp.
6. S.I. unit of resistance is ohm.

RESISTIVITY

Resistance is directly proportional to the length and inversely proportional to the area.

So, R α L/A

R = ρL/A

• Here ρ(rho) is the resistivity of the material of conductor. It is also known as the specific resistance.
• Its unit is ohm – meter.
• Resistivity of alloys are much higher than those of pure metals.
•  Nichrome, Constantan and Manganin are the alloys. Due to this they have high resistance and produce lots of heat and thus they use in hair dryers etc.

RESISTANCE CAN ARRANGE IN TWO FORMS: SERIES & PARALLEL

Resistance in series (R_S = R₁+ R₂ + R₃)

Let R1, R2 and R3 are the three resistances that connect in series.

                                  V = V₁ + V₂ + V₃

As we know that     V = IR   So,

          IR = IR₁ + IR₂ + IR₃

          IR = I (R₁ + R₂ + R₃)

           (R_S = R₁+ R₂ + R₃)

Resistance in parallel (1/R_P = 1/R₁ + 1/R₂ + 1/R₃)

Let three resistances R1, R2 and R3 are connect in parallel.

I = I₁ + I₂ + I₃

As we know that      V = IR or I = V/R

So,

            V/R = V/R₁ + V/R₂ + V/R₃

            V/R = V (1/R₁ + 1/R₂ + 1/R₃)

           1/R_P = (1/R₁ + 1/R₂ + 1/R₃)

DISADVANTAGE OF SERIES CIRCUIT

1. If one electrical appliances stops working due to some defect, then all other appliances also stops working at that instant of time.
2. All the electric appliances have only one switch due to which they cannot be turned on or off separately.
3.  The appliances do not get the same voltage as that of power supply line.
4. In the series connection of the electrical appliances, overall resistances of circuit increases too much due to which current supply become low.

ELECTRIC POWER

Electric power is electrical work done per unit time.

Power = work done/time taken

P = W/T

• S.I. unit of power is watt.
• Electric power is the rate at which electrical energy consumed.
• P = V X I
• P = I²R
• P = V²/R
• In concept of electric energy we use power in kilowatt and time in hour.

E = P X T

1KWh = 3.6 X 106J

1KWh = 1000 Watt