what is electricity?? ppt

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1. Electric Current and Circuit Electric Potential & Potential Difference Circuit Diagram Ohm’s Law Factors on which the Resistance of a conductor Depends -Resistance & Resistivity Resistance of a System of Resistors-Series/Parallel Heating Effects of Current Electric Power TOPICS TO BE COVERED

2. It is a form of Energy made up of charges that can produce light, heat or motion Static electricity – electric charges at rest Current electricity – electric charges -motion What is Electricity

3. Flow of electric charge constitutes electric current Electric Current

4. Other examples – glass rod rubbed with silk cloth An ebonite rod rubber with woolen cloth What is charge?

5. Positive Charge Negative Charge Property of Electric Charges: Opposite charges attract each other Similar charges repel each other Types of Electric Charges

6. SI unit of electric c harge is coulomb which is denoted by C One Coulomb is that quantity of electric charge which exerts a force of 9 x 10 9 Newton's on an equal charge placed at a distance of 1 metre from it. Electric Charge

7. Q = n x e where – Q – charge in coulombs n- number of electrons(integer) e – charge of one electron = 1.6 x 10 -19 C So, 1 C = n x 1.6 x 10 -19 C n = 1C/1.6 x10 -19 C n = 6.25 x 10 18 electrons Hence, we can say that one coulomb of electric charge contains 6.25 x 10 18 electrons Number of electrons in 1 C of charge

8. Flow of electric charge constitutes electric current Definition: Electric current is expressed by the amount of charge flowing through a particular area in unit time. It is the rate of flow of electric charges. Denoted by I Electric Current

9. The magnitude of an electric current is defined as the amount of electrons passing through a cross-sectional area of the wire within a given interval of time. Current = amount of electrons flowing through the cross-section of the wire I = Q/ t Where, I – amount of current Q- amount of electrons flowing through a cross section t- time taken Electric Current

10. The SI unit of current is Ampere , named after the great physicist, Andre Marie Ampere Since the SI unit of charge is coulomb and that of time is second, we define 1 ampere as: 1 ampere is 1 coulomb of charge flowing through a conductor in one second. 1 A = 1 C/ 1 s or 1 C = 1A x 1S So, 1 coulomb can be defined as the amount of charge that passes through a conductor when 1 ampere current flows through the conductor for 1 second. Electric current

11. An ammeter is used to measure the electric current in a circuit. It is always connected in series. Ammeter

12. The smaller units of current are expressed in milliampere (mA) and micro ampere(µA). The relation is given by: 1mA = 10 -3 A 1µA = 10 -6 A Smaller units

13. Direction of Electric Current

14. So, Direction of current for - Electronic current is – from –ve to +ve - Conventional current – from +ve to -ve

15. What does an electric current mean? Define the unit of current. Calculate the number of electrons constituting one coulomb of charge. An electric bulb draws a current of 0.25 A for 20 min. calculate the amount of electric charge that flows through the circuit. Calculate the current in a circuit if 500 C of charge passes through it in 10 min. An electric iron draws a current of 0.6 A when the voltage is 100 volt. Calculate the amount of electric charge flowing through it in one hour. HW

16. Why do we get electric shock, if we touch a live wire? Birds sitting on a live wire, does not get electrocuted, why? Electric Potential

17. Electric potential at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point. It is denoted by V Its unit is Volt A potential of 1 volt at a point means that 1 joule of work is done in moving 1 unit positive charge(1 C) from infinity to that point. Electric potential

18. The difference in electric potential between two points is known as potential difference. The potential difference between two points in an electric circuit is defined as the amount of work done in moving a unit charge from one point to the other point. So, Potential difference = Work done Quantity of charge moved Potential Difference

19. V = W/ Q Where, V –potential difference W – work done Q – Quantity of charge moved

20. SI unit of potential difference is volt and denoted by V The potential difference between two points is said to be 1 volt if 1 joule of work is done in moving 1 coulomb of electric charge from one point to the other. So, 1 volt = 1 joule/ 1 coulomb Or 1 V = 1J/ 1C Potential Difference

21. Potential difference is measured by means of an instrument called voltmeter Voltmeter is always connected in parallel Voltmeter has high resistance Voltmeter

22. Name a device that helps to maintain a potential difference across a conductor. What is meant by saying that the potential difference between two points is 1 V? How much work is done in moving a charge of 2C across two points having a potential difference 12V? How much work is done in moving a charge of 2 coulombs from a point at 118 volts to a point at 128 volts? How much energy is given to each coulomb of charge passing through a 6 V battery? Hw

23. A continuous conducting path consisting of wires and other resistances( like electric bulb etc )and a switch, between the two terminals of a cell or a battery along which an electric current flows, is called a circuit. Electric Circuits

24. Symbols For Electrical Components

25. A diagram which indicates how different components in a circuit have been connected by using the electrical symbols for the components, is called a circuit diagram Circuit Diagram

26. Activity

27. The ratio of V/I is same i.e. a constant value. The graph drawn between V-I is a straight line that passes through the origin of the graph, showing that current is directly proportional to the potential difference. Observation

28. States that: The potential difference, V , across the ends of a given metallic wire in an electric circuit is directly proportional to the current, I, flowing through it, provided its temperature remains the same(constant) Ohm’s Law given by George Simon Ohm

29. V α I V = Constant x I V/ I = R Where V = Potential difference I = Electric current R = Resistance

30. Resistance is the property of a conductor due to which it opposes the flow of current flowing through it. R = V/I The unit of resistance is Ohm represented by Ω If the potential difference V is 1 volt and the current I is 1 ampere, then resistance R is 1 ohm. 1 ohm = 1 volt/ 1 ampere So, 1 ohm is the resistance of a conductor such that when a potential difference of 1 volt is applied to its ends, a current of 1 ampere flows through it. Resistance

31. I = V/R So, The current is directly proportional to pd and The current is inversely proportional to resistance . Thus if pd is doubled, the current flowing will be doubled and if pd is halved, the current also gets halved. But current is inversely proportional to resistance, so if resistance is doubled then current gets halved and if resistance is halved, then the current gets doubled.

32. State Ohm’s Law. How it can be verified experimentally. How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 ohm? How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 ohm? The potential difference between the terminals of an electric heater is 60V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V. Hw

33. Potential difference between two points of a wire carrying 2 ampere current is 0.1 volt. Calculate the resistance between these points. A current of 5 A is flowing through a resistor of 15 ohm. Calculate the potential difference between the ends of the resistor. Q 3 of text book pg 209 Q 8 of text book pg 221 HOMEWORK