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# Electricity

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## ElectricityPresentation Transcript

• www.swaddhyay.jnanaprabodhini.org 1 Electricity Milind Naik
• www.swaddhyay.jnanaprabodhini.org2 Static Electricity!(stationary/rest) Charge that stays on an object When something gives up or gains electrons Does not move along a wire or other conductor
• www.swaddhyay.jnanaprabodhini.org3 Electric Charge Measured in COULOMBS Six million trillion electrons is about - 1 C. Six million trillion protons is about + 1 C.
• www.swaddhyay.jnanaprabodhini.org4 Atoms have protons, neutrons, and electrons. Same number of protons and electrons, it is balanced and neutral Sometimes electrons get knocked out of place – free electrons If they go to where other electrons are missing, this creates a current of electricity!
• www.swaddhyay.jnanaprabodhini.org5 •If we bring a plastic comb near some very tiny pieces of paper, it will not have any effect on them. •If we rub a plastic comb with dry hair and then brought near some very tiny pieces of paper, we find that the comb attracts the pieces of paper towards itself •These observations are explained by saying that initially the comb is electrically neutral so it has no effect on tiny pieces of paper •When the comb is rubbed with dry hair then it gets electric charge •Other examples: silk cloth and glass rod, ebonite rod woolen cloth
• www.swaddhyay.jnanaprabodhini.org6 •Opposite charges(unlike) attract each other •Similar charges repel each other
• www.swaddhyay.jnanaprabodhini.org7 •The SI unit of electric charge is coulomb which is denoted by C •One coulomb is that quantity of electric charge which exerts a force of 9 X 109 Newton on an equal charge placed at a distance of 1 m from it. q1q2 F= Q ------------ r2 • A proton possesses a positive charge of 1.6 x 10 –19 C whereas an electron possesses a negative charge of 1.6 x 10 –19 C
• www.swaddhyay.jnanaprabodhini.org8 Calculate the number of electrons constituting one coulomb of charge. We know that the charge of an electron is 1.6 X 10 –19 C Now if charge is 1.6 x 10 –19 C, No. of electrons = 1 1 If charge is 1 C, No. of electrons = ----------------------- x 1 1.6 x 10 –19 C = 6.25 x 10 18 THUS 1C IS EQUIVALENT TO CHARGE ON 6.25 x 10 18 ELECTRONS
• www.swaddhyay.jnanaprabodhini.org11 Electric Potential Energy This spring has more PE when it is compressed
• www.swaddhyay.jnanaprabodhini.org12 Electric Potential Energy This spring has more SPE when it is compressed Likewise, these charges will have more potential energy when they are pushed closer
• www.swaddhyay.jnanaprabodhini.org13 Electric Potential Energy PE equals the amount of work done to move a charge from one place to another.
• www.swaddhyay.jnanaprabodhini.org15 Electric Potential Energy Which will have the larger electric potential energy?
• www.swaddhyay.jnanaprabodhini.org16 Electric Potential Energy A – because it requires work to move it away from the negative charge.
• www.swaddhyay.jnanaprabodhini.org17 Electric Potential (volts) EP = work/charge
• www.swaddhyay.jnanaprabodhini.org18 Electric Potential (volts) Example: 1000 joules of work is done to move the charge q from far away to the place indicated. If q = 10 C, what is the electric potential at the new location?
• www.swaddhyay.jnanaprabodhini.org19 Electric Potential (volts) Example: 1000 joules of work is done to move the charge q from far away to the place indicated. If q = 10 C, what is the electric potential at the new location? Voltage = work/charge V = 1000 J/10C = 100 Volts
• www.swaddhyay.jnanaprabodhini.org20 Electric Potential (volts) What if the charge in the previous problem were now 100 C instead of 10? What would happen to the EP?
• www.swaddhyay.jnanaprabodhini.org21 Electric Potential (volts) What if the charge in the previous problem were now 100 C instead of 10? What would happen to the EP? IT WOULD BE THE SAME!!! Work would also increase
• www.swaddhyay.jnanaprabodhini.org22 Electric Potential (volts) Electric potential is associated with LOCATION, not CHARGE
• www.swaddhyay.jnanaprabodhini.org23 Electric Potential vs. Potential Energy Which charge has more electric potential? Which has more potential energy?
• www.swaddhyay.jnanaprabodhini.org24 Is 5000 Volts Dangerous?
• www.swaddhyay.jnanaprabodhini.org25 Is 5000 Volts Dangerous? NOPE! When 1 million electrons are added to a neutral balloon, it has an electric potential of 5000 volts
• www.swaddhyay.jnanaprabodhini.org26 Potential Difference (voltage) Difference in electric potential between two points.
• www.swaddhyay.jnanaprabodhini.org27 Potential Difference (voltage) Difference in electric potential between two points. Potential difference between A and B is 0 A B
• www.swaddhyay.jnanaprabodhini.org28 Potential Difference (voltage) Difference in electric potential between two points. Now there is a potential difference A B
• www.swaddhyay.jnanaprabodhini.org29 Potential Difference Batteries provide potential difference between one end of the circuit and the other
• www.swaddhyay.jnanaprabodhini.org30 Potential Difference Batteries provide potential difference between one end of the circuit and the other Charges flow from high to low electric potential
• www.swaddhyay.jnanaprabodhini.org31 Potential Difference (voltage) Why aren’t birds on power lines shocked?
• www.swaddhyay.jnanaprabodhini.org32 Potential Difference (voltage) Why aren’t birds on power lines shocked? The Potential Difference between their feet is zero! (0 voltage)
• www.swaddhyay.jnanaprabodhini.org33 From infinity AB 1 J2 J 1V +1C +1C+1C
• www.swaddhyay.jnanaprabodhini.org34 Electric Potential The 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
• www.swaddhyay.jnanaprabodhini.org35 •Potential is denoted by the symbol 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 from infinity to that point.
• www.swaddhyay.jnanaprabodhini.org36 Potential Difference 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 positive charge from one point to the other point Work done Potential difference = -------------------------------- Quantity of charge moved
• www.swaddhyay.jnanaprabodhini.org37 •SI Unit of P.D. is Volt. 1 Joule 1 Volt = -------------------------- 1 Coulomb
• www.swaddhyay.jnanaprabodhini.org38 Current Electricity!(motion) Electric charges are called electric current. Free electrons continuously move to spaces where electrons are missing.
• www.swaddhyay.jnanaprabodhini.org39 Conductors A conductor is a material through which current can pass easily An insulator is a material through which electricity cannot flow
• www.swaddhyay.jnanaprabodhini.org40 Metal alloys such as Nichrome, Manganin, and Constantan which are used for making heating elements of electrical appliances are also conductors but their electrical conductivity is much less than that of pure metals
• www.swaddhyay.jnanaprabodhini.org41 The presence of “ free electrons” in a substance makes it conductor
• www.swaddhyay.jnanaprabodhini.org42 The potential difference(Voltage) is measured by means of an instrument called voltmeter • The voltmeter is always connected in parallel across the points where the potential is to be measured •Voltmeter has a high resistance so that it takes a negligible current from the circuit.
• www.swaddhyay.jnanaprabodhini.org43 How much work is done in moving a charge of 2 coulombs from a point at 118 volts to a point at 128 volts?
• www.swaddhyay.jnanaprabodhini.org44 How much energy is given to each coulomb of charge passing through a 6 V battery?
• www.swaddhyay.jnanaprabodhini.org45 Electric Current When two charged bodies at different electric potentials are connected by a metal wire then electric charges will flow from the body at higher potential to the one at lower potential till they acquire the same potential. This flow of charges in the metal wire constitutes an electric current
• www.swaddhyay.jnanaprabodhini.org46 The magnitude of electric current in a conductor is the amount of electric charge passing through a given point of the conductor in one second. Q I = ------ t
• www.swaddhyay.jnanaprabodhini.org47 •The SI unit of electric current is ampere (A) •When 1 coulomb of charge flows through any cross section of a conductor in 1 second, the electric current flowing through it is said to be 1 ampere. 1 coulomb 1 ampere = --------------------- 1 second
• www.swaddhyay.jnanaprabodhini.org48 •Some times smaller units are used •Milli-ampere(mA)= 1/1000 Ampere •Micro-ampere(µA)= 1/1000000 Ampere
• www.swaddhyay.jnanaprabodhini.org49 The current (I) is measured by means of an instrument called ammeter • The ammeter is always connected in series with the points where the current is to be measured •Ammeter has a low resistance so that it may not change the value of current from the circuit.
• www.swaddhyay.jnanaprabodhini.org50 An electric bulb draws a current of 0.25 A for 20 minutes. Calculate the amount of electric charge that flows through the circuit.
• www.swaddhyay.jnanaprabodhini.org51 How to get continuous flow of electric current •The simplest way is to connect the cell or a battery. •Due to the chemical reactions going on inside the cell or battery, a potential difference is maintained between its terminals
• www.swaddhyay.jnanaprabodhini.org52 The CELLThe CELL The cell stores chemical energy and transfers it to electrical energy when a circuit is connected. When two or more cells are connected together we call this a Battery. The cells chemical energy is used up pushing a current round a circuit.
• www.swaddhyay.jnanaprabodhini.org53 What is an electric current? An electric current is a flow of microscopic particles called electrons flowing through wires and components. + - In which direction does the current flow? from the Negative terminal to the Positive terminal of a cell.
• www.swaddhyay.jnanaprabodhini.org54 Direction of electric current •The conventional direction of electric current is from positive terminal of a cell to the negative terminal through the circuit •The actual flow of electrons is however from negative terminal to positive terminal of a cell.
• www.swaddhyay.jnanaprabodhini.org55 How current flows in a wire When the metal wire has not been connected to a source of electricity like a cell or a battery, then the electrons present in it move at random in all the directions between the atoms of the metal wire as shown in figure
• www.swaddhyay.jnanaprabodhini.org56 When a source of electricity like a cell or a battery is connected between the ends of the metal wire, then an electric force acts on the electrons present in the wire and start moving from negative end to positive end of the wire.
• www.swaddhyay.jnanaprabodhini.org57 Electric circuits A continuous conducting path consisting of wires and other resistances and a switch between the two terminals of a cell along which an electric current flows is called a circuit
• www.swaddhyay.jnanaprabodhini.org58 simple circuitssimple circuits Here is a simple electric circuit. It has a cell, a lamp and a switch. To make the circuit, these components are connected together with metal connecting wires. cell lampswitch wires
• www.swaddhyay.jnanaprabodhini.org59 circuit diagramcircuit diagram cell switchlamp wires Scientists usually draw electric circuits using symbols;
• www.swaddhyay.jnanaprabodhini.org60 Open and Closed Circuits What will happen if the switch is lifted?
• www.swaddhyay.jnanaprabodhini.org61 Circuit diagrams 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
• www.swaddhyay.jnanaprabodhini.org62 Symbols for electrical components
• www.swaddhyay.jnanaprabodhini.org64 Ohms law At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends • I ∝ V • V= IR • V/I = R  Current is directly proportional to PD  Current is inversely proportional to R
• www.swaddhyay.jnanaprabodhini.org65 Resistance of a conductor The property of a conductor due to which it opposes the flow of current through it is called resistance 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.
• www.swaddhyay.jnanaprabodhini.org66 Problem:Potential difference between two points of a wire carrying 2 ampere current is 0.1 volt. Calculate the resistance between these points
• www.swaddhyay.jnanaprabodhini.org67 A simple electric circuit has a 24 V battery and resistor of 60 ohms. What will be the current in the circuit? The resistance of the connecting wires is negligible.
• www.swaddhyay.jnanaprabodhini.org68 An electric iron draws a current of 3.4 A from the 220 V supply line. What current will this electric iron draw when connected to 110V supply line?
• www.swaddhyay.jnanaprabodhini.org69 Graph between V and I Current is directly proportional to potential difference
• www.swaddhyay.jnanaprabodhini.org70 The values of current I flowing through a coil for the corresponding values of the pd V across the coil are shown below: I(A) 0.05 0.10 0.20 0.30 0.40 V(V) 0.85 1.70 3.5 5.0 6.8 Plot a graph between V & I and calculate the resistance of the coil
• www.swaddhyay.jnanaprabodhini.org73 types of circuittypes of circuit There are two types of electrical circuits; SERIES CIRCUITS PARALLEL CIRCUITS
• www.swaddhyay.jnanaprabodhini.org74 Series CircuitSeries Circuit  A circuit that onlyA circuit that only has one path forhas one path for current to flowcurrent to flow through is called athrough is called a series circuitseries circuit.. If the path is broken, no current flows through the circuit.
• www.swaddhyay.jnanaprabodhini.org75 Parallel Circuit A type of circuit that has more than one path for current is called a parallel circuit. If the path is broken, the current continues to flow through the circuit.
• www.swaddhyay.jnanaprabodhini.org76 The components are connected end-to-end, one after the other. They make a simple loop for the current to flow round. SERIES CIRCUITS If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.
• www.swaddhyay.jnanaprabodhini.org77 PARALLEL CIRCUITS The current has a choice of routes. The components are connected side by side. If one bulb ‘blows’ there is still be a complete circuit to the other bulb so it stays alight.
• www.swaddhyay.jnanaprabodhini.org78 measuring current Electric current is measured in amps (A) using an ammeter connected in series in the circuit. A
• www.swaddhyay.jnanaprabodhini.org79 measuring current A A This is how we draw an ammeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT
• www.swaddhyay.jnanaprabodhini.org80 measuring current SERIES CIRCUIT PARALLEL CIRCUIT • current is the same at all points in the circuit. 2A 2A 2A • current is shared between the components 2A2A 1A 1A
• www.swaddhyay.jnanaprabodhini.org81 copy the following circuits and fill in the missing ammeter readings. ? ? 4A 4A 4A 3A? ? 1A ? 3A 1A 1A
• www.swaddhyay.jnanaprabodhini.org82 measuring voltage The ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter V
• www.swaddhyay.jnanaprabodhini.org83 Different cells produce different voltages. The bigger the voltage supplied by the cell, the bigger the current. measuring voltage Unlike an ammeter a voltmeter is connected across the components Scientist usually use the term Potential Difference (pd) when they talk about voltage.
• www.swaddhyay.jnanaprabodhini.org84 measuring voltage V This is how we draw a voltmeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT V
• www.swaddhyay.jnanaprabodhini.org85 V measuring voltage V V V
• www.swaddhyay.jnanaprabodhini.org86 series circuit 1.5V • voltage is shared between the components 1.5V 3V
• www.swaddhyay.jnanaprabodhini.org87 • voltage is the same in all parts of the circuit. 3V parallel circuit 3V 3V
• www.swaddhyay.jnanaprabodhini.org88 measuring current & voltage copy the following circuits on the next two slides. complete the missing current and voltage readings. remember the rules for current and voltage in series and parallel circuits.
• www.swaddhyay.jnanaprabodhini.org89 measuring current & voltage V V 6V 4A A A a)a)
• www.swaddhyay.jnanaprabodhini.org90 measuring current & voltage V V 6V 4A A A A b)b)
• www.swaddhyay.jnanaprabodhini.org91 answers 3V 3V 6V 4A 4A 6V 6V 6V 4A 4A 2A 2A 4A a)a) b)b)
• www.swaddhyay.jnanaprabodhini.org92 Combination Circuit What will happen to the circuit if one of the motors fails to function? What will happen if one of the bulbs fails to function?
• www.swaddhyay.jnanaprabodhini.org93 Types of Currents Direct Current (DC) Alternating Current (AC)
• www.swaddhyay.jnanaprabodhini.org94 AC DC Electrical Power Sources Direction of electrons reverses Electricity is generated by coal, water, fossil fuels, or nuclear reaction at a generating station Electrons flow in one direction Electricity is generated by stored chemicals, radiation, wind, or fuel Can be portable
• www.swaddhyay.jnanaprabodhini.org95 Alternating Current The power that comes fromThe power that comes from a power plant is calleda power plant is called alternating currentalternating current (AC).(AC). The direction of the currentThe direction of the current reverses, or alternates, 60reverses, or alternates, 60 times per second (in thetimes per second (in the U.S.) or 50 times perU.S.) or 50 times per second (in Europe/ India, forsecond (in Europe/ India, for example). The power that isexample). The power that is available at a wall socket inavailable at a wall socket in the United States isthe United States is 120-120- volt, 60-cycle AC powervolt, 60-cycle AC power..
• www.swaddhyay.jnanaprabodhini.org97 From this lesson you will learn: The effects of electric shocks. How a plug should be wired correctly. How a plug works. How electrical safety devices work. The various faults that can develop.
• www.swaddhyay.jnanaprabodhini.org98 Electricity Electricity can be supplied from either: • A battery. • The mains supply.
• www.swaddhyay.jnanaprabodhini.org99 Electricity The main advantage of electrical energy is that it can be transported over large distances to our homes. Wires carry electricity from power stations to our homes/schools/offices.
• www.swaddhyay.jnanaprabodhini.org100 Electric Shocks Electricity is dangerous and can kill!! An electric shock can: You can get an electric shock from anything which is plugged in or connected to the mains supply. • Affect your muscles. • Affect your nerves. • Paralyse you. • Stop your heart beating.
• www.swaddhyay.jnanaprabodhini.org101 Electrical Safety The wires which carry electricity consist of two parts: • The metal wires. • The plastic coating round the metal wires.
• www.swaddhyay.jnanaprabodhini.org102 Electrical Safety The metal wires act as a conductor of electricity. The plastic coating acts as an insulator which prevents people from being electrocuted. Conductors are materials which allow electricity to pass through them easily. Insulators are materials which do not allow electricity to pass through them easily.
• www.swaddhyay.jnanaprabodhini.org103 The Plug Electrical cables allow you to: • Plug appliances into the mains supply. • Draw electricity from the mains supply.
• www.swaddhyay.jnanaprabodhini.org104 The Plug Most electric cables normally contain three wires: Each of these three wire have different colours of insulation. • The live wire. • The neutral wire. • The earth wire.
• www.swaddhyay.jnanaprabodhini.org105 The Plug You have to remember the names and colours of each of these three wires. You also have to remember the position of each of these three wires in a standard plug. Wire Insulation Colour Location LIVE BRown BR – bottom right NEUTRAL BLue BL – bottom left EARTH Green/Yellow Centre
• www.swaddhyay.jnanaprabodhini.org106 Electrical Safety It is very important that all plugs are wired correctly. If they are not, then a number of things can go wrong!!!
• www.swaddhyay.jnanaprabodhini.org107 Electrical Safety Appliances have three safety devices: • The fuse. • The earth wire. • The switch. These devices are designed to stop you from being electrocuted and to prevent the appliance from being damaged.
• www.swaddhyay.jnanaprabodhini.org108 The Fuse A fuse is a thin piece of wire which will melt when too much current passes through it. A 3A fuse will melt when the current is greater than 3A. When a fuse has blown, the wire inside it has melted. Current is a flow of electricity and is measured in amps (A). Example
• www.swaddhyay.jnanaprabodhini.org109 The Fuse When the wire melts, all current is stopped from reaching the appliance and switches it off. The fuse stops a large current from flowing through the appliance which could cause wires to overheat, melt or catch fire.
• www.swaddhyay.jnanaprabodhini.org110 The Switch Together, the fuse and switch control the amount of electricity that enters an appliance. The fuse and the switch are connected to the live wire. Electricity comes in through the live wire. If the fuse is blown, or the switch is off, then the electricity cannot reach the appliance.
• www.swaddhyay.jnanaprabodhini.org111 The Earth Wire Plugs have 3 pins on them. The live and neutral pins allow electricity to pass through the appliance and cause it to work. The earth wire does nothing unless something goes wrong.
• www.swaddhyay.jnanaprabodhini.org112 What can go wrong! The most dangerous thing that can happen is that the live wire can become loose inside an appliance and touches the casing. This makes the casing LIVE! If you touch the LIVE casing, you could be electrocuted as you are providing a path for the electricity to flow.
• www.swaddhyay.jnanaprabodhini.org113 Prevention To prevent electrocution, the earth wire is connected to the casing of the appliance. If the live wire touches the casing, the earth wire provides a path for the electricity to flow. This blows the fuse and switches the appliance off, leaving you safe.