Notes of science ch 12 eletricity of class 10
Answers
Answer:
Electricity: Electric current, electric circuit, voltage or electric potential, resistance and (Ohm’s law).
Electric Current: The flow of electric charge is known as Electric Current, Electric current is carried by moving electrons through a conductor.
By convention, electric current flows in the opposite direction to the movement of electrons
Expression of Electric Current: Electric current is denoted by the letter ‘I’. Electric current is expressed by the rate of flow of electric charges. Rate of flow means, the amount of charge flowing through a particular area in unit time.
Properties of Electric Charge:
(i) Unlike charges attract each other and like charges repel each other.
(ii) The.force between two charges varies directly as the product of two charges and inversely as the square of the distance (r) between both charges (q1 and q2).
Galvanometer: It is a device to detect current in an electric circuit
Resistance: Resistance is the property of conductor which resists the flow of electric current through it.
S.I. unit of resistance is ohm. Ohm is denoted by Greek letter ‘Q’
Resistance: Resistance is a property of conductor due to which it resists the flow of electric current through it. A component that is used to resist the flow of electric current in a circuit is called a resistor.
In practical application, resistors are used to increase or decrease the to electric current.
Variable Resistance: The component of an electric circuit which is used to regulate the current, without changing the voltage from the source, is called variable resistance.
Rheostat: This is a device which is used in a circuit to provide variable resistance.
Cause of Resistance in a Conductor: Flow of electrons in a conductor is electric current. The positive particles of conductor create hindrance to flow of electrons, because of attraction between them, this hindrance is the cause of resistance in the flow of electricity.
Factors on Which Resistance of a Conductor Depends: Resistance in a conductor depends on nature, length and area of cross section of the conductor.
(i) Nature of Material: Some materials create least hindrance and hence, are called good conductors. Silver is the best conductor of electricity. While some other materials create more hindrance in the flow of electric current, i.e. flow of electrons through them. Such materials are called bad conductors. Bad conductor are also known as insulators. Hard plastic is the one of the best insulators of electricity.
(ii) Length of Conductor: Resistance (R) is directly proportional to the length of the conductor. This means, resistance increases with increase in length of the conductor. This is the cause that long electric wires create more resistance to the electric current. Thus, Resistance (R) ∝ length of conductor (l)
or, R ∝ l …(i)
(iii) Area of Cross Section: Resistance R is inversely proportional to the area of cross section (A) of the conductor. This means R will decrease with an increase in the area of conductor and vice versa. More area of conductor facilitates the flow of electric current through more area and thus, decreases the resistance. This is the cause that thick copper wire creates less resistance to the electric current.
Thus, resistance (R) ∝ 1/Area of cross section of conductor (A)
or, R ∝ \frac { l }{ A } ….(ii)
From equations (i) and (ii)
R ∝ \frac { l }{ A }
R = ρ \frac { l }{ A }
Where, ρ (rho) is the proportionality constant. It is called the electrical resistivity of the material of conductor.
From equation (iii) RA = ρl ⇒ ρ = \frac { RA }{ l } ..(iv)
The S.I. of Resistivity: Since, the S.I. unit of R is Q, S.I. unit of area is m2 and S.I. unit of length is m. Hence, unit of resistivity (ρ) = \frac { \Omega \times { { m }^{ 2 } } }{ m } = Ωm
Thus, S.I. unit of resistivity (ρ) is Ωm.
Resistivity: It is defined as the resistance offered by a cube of a material of side 1m when current flows perpendicular to its opposite faces. It’s S.I. unit is ohm-meter (Ωm).
Resistivity, ρ = \frac { RA }{ l }
Resistivity is also known as specific resistance.
Resistivity depends on the nature of the material of the conductor.
Materials having a resistivity in the range of 10-8 Ωm to 10-6 Ωm are considered as very good conductors. Silver has resistivity equal to 1.60 × 10-8 Ωm and copper has resistivity equal to 1.62 × 10-8 Ωm.
Rubber and glass are very good insulators. They have a resistivity in the order of 10-12 Ωm to 10-8 Ωm.
The resistivity of materials varies with temperature.
Combination of resistors (Series and Parallel combination), the heating effect of electric current and electric power.
Combination of Resistors
(i) Series combination
(ii) Parallel combination.
the current flowing through each resistor is the same and is equal to the total current.
Answer:
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Explanation:
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