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Chapter 9 - Current Electricity

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Published in: Physics
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The chapter includes the concept of charge, electric current and potential difference.

Anil N / Dehradun

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Teaches: Chemistry, Mathematics, Physics, Science, Vedic Maths, CET, IIT JEE Mains

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  1. CURRENT ELECTRICITY Charge: Like mass, the charge is the fundamental property of matter. There are two types of charge: - l. Positive charge 2. Negative charge Positive and Negative Charge: The charge acquired on the glass rod when rubbed with silk is called a positive charge and the charge acquired on an ebonite rod when rubbed with wool is called negative charge. Properties of Electric Charge: 1. Unlike charges attract each other and like charges repel each other. 2. The force between two charges (qi & €12) varies directly as the product of charges and inversely as the square of the distance (r) between them. or, F = k k = constant S.I. unit of charge is coulomb (C). Electricity: Keywords: Electric current, electric circuit, voltage or electric potential, resistance and Ohm's law. Electric Current: The rate of flow of electric chares through a conductor is called Electric current. 'Rate of flow' means, the amount of charge flowing through a particular area in unit time. Electric current is denoted by the letter 'I'. If a net electric charge (Q) flows through a cross-section of a conductor in time t, then, Charge Electric current (I) = time S.I. Unit of current is Ampere (A). Electric potential: The amount of electric potential energy at a point is called electric potential. Potential Difference: The difference in the amount of electric potential energy between two points in an electric circuit is called electric potential difference.
  2. Electric potential difference is known as voltage, which is equal to the amount of work done to move the unit charge between two points against static electric field. 0.4 so, Work done Voltage Charge S.I. unit of electric potential difference is volt and denoted by 'V'. Conductor: The material which can allow the flow of electrons through itself is called conductor. Insulator: The material which does not allow the flow of electrons through itself is called insulator. Ohm's Law: According to this law, under the constant physical conditions the potential difference across the conductor is directly proportional to the current flowing through the conductor. i.e. V ul v=1R where R is constant for the given conductor at a given temperature is called resistance. Resistance: Resistance is the property of conductor which resists the flow of electric current through it. S.I. unit of resistance is ohm. 0.3 0.2 Voltage (V) Graph of ohm's law
  3. Combination of Resistance in series: 2. In this combination the current across every component is same but potential across every component is different. If resistance RI, R2 and R3 are connected in series with a battery of Potential V, the equivalence resistance of the combination : R=RI + R2 + Combination of Resistance in parallel: l. In this combination the current across every component is different. But potential across every component is the same. 2. If resistance RI, R2 and R3 are connected in parallel with a battery of Potential V, then equivalence resistance of combination 1 R 1 1 1 RI Factors on which Resistance in a conductor depends: - 1. 2. 3. Nature of Material: Some materials create least hindrance and hence, are called good conductor. Silver is the best conductor of electricity. While some other materials create more hindrance in the flow of electric current, such materials are called bad conductors. Bad conductors are also known as insulators. Hard plastic is the best insulators of electricity. Length of conductor: Resistance is directly proportional to the length of the conductor. This means, resistance increases with increase in the length of the conductor. Area of Cross Section: Resistance is inversely proportional to the area of cross section of the conductor. This means resistance will decrease with an increase in the area of conductor and vice versa. 1
  4. Electric Power (P): The electric work done per unit time is called electric power. OR The electric energy consumed per unit time is called electric power. I.e., Electric Work done Elecric Power = Time Taken Heat generated by electric current: Some amount of heat is produced when current is flow through the conductor, the amount of heat calculated by: H- 12RT

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