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R, R. R,, oe » SAA, A, +- v 1! | > | |, , swe J Chapter - 12, , , , Electricity, , , , , , ¢ Charge is a fundamental particle in an atom. It may be positive or, negative., , e Like charges repel each other., ¢ Unlike charges attract each other., Coulomb (C) : S. I. unit of charge, 1 Coulomb charge = Charge present on approx. 6 x 10'* electrons, ¢ Charge on | electron = Negative charge of 1.6 x 10°" C, Q=ne, Where Q = Charge (total), n=No. of electrons, e = Charge on | electron, , Current (I) : The rate of flow of charge is called current., , Charge, Current = ie, , , , Time, , Q, , [= —, , S_ I. unit of current = Ampere (A)!, 1A=1 Cs"!, ]1mA=107A, 1uA=10°A, , Current is measured by Ammeter. Its symbol 1s A, , , , Scanne d with CamScanner
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Ammeter has low resistance and always connected in series., , Direction of current is taken opposite to flow of electrons as electrons were, not known at the time when the phenomenon of electricity was discovered, first and current was considered to be flow of positive charge., , Potential Difference (V) : Work done to move a unit charge from one point to, , anioIek I Volt : When I joule work is done, W in carrying one Coulomb charge, V=— _ then potential difference is called, g ! volt., S. I. unit of Potential difference = Volt (V), 1V=1JC', , 1 Volt: When | joule work is done in carrying one Coulomb charge then potential, difference is called 1 volt., , Voltmeter : Instrument to measure potential difference., , ° It has high resistance and always connected in parallel. Symbol is, + _, V, , , , ° Cell is the simplest device to maintain potential difference., , ° Current always flow from higher potential to lower potential., , Symbols of Some Commonly Used Components in Circuit :, , , , , , , , , , Electric cell LS, Battery FY |, Key (open) | —Q-—, Key (closed) ci, , Wire joint wahins, , Wire Crossing (without join) :, , Electric bulb ©) or, Resistance : —\WWWW\Rheostat yh ult, | or “WWWW\, , , Ammeter, , Scanne d with CamScanner
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+, , , , Voltmeter Ww, , Ohm’s Law : Potential difference across the two points of a metallic, conductor is directly proportional to current passing through the circuit, provided that temperature remains constant., , ¢ Mathematical expression for Ohm’s law :, Val, V=IR, R is a constant called resistance for a given metal., , e \V-I graph for Ohm’s law :, , Potential Difference >, (V), , , , , , Current (I) >, , Resistance (R) : It is the property of a conductor to resist the flow of charges, , , , through It., © Ohm (Q): S. I. unit of resistance., 1ohm = — WI ‘al differ iP a hr, heen ‘hen potential difference is 1 V and current through, , the circuit is 1 A, then resistance is 1 ohm., , Rheostat : Variable resistance is a component used to regulate current, without changing the source of voltage., , Factors on which the Resistance of a Conductor depends :, Resistance of a uniform metallic conductor is, (i) directly proportional to the length of conductor,, (ii) inversely proportional to the area of cross-section,, (iii)directly proportional to the temperature and, (iv)depend on nature of material., , Resistivity (P ) : Itis defined as the resistance offered by a cube ofa material, of side 1 m when current flows perpendicular to its opposite faces., , Scanne d with CamScanner
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Resistors in Series:, , , , Its S.I. unit is ohm-metre (Qm),., , R, R, R,, , Resistivity does not change with change in length or area of cross-section, but it changes with change 1n temperature., , Range of resistivity of metals and alloys is 10°* to 10° Qm., Range of resistivity of insulators is 10'* to 10'7 Om., Resistivity of alloy 1s generally higher than that of its constituent metals., , Alloys do not oxidize (burn) readily at high temperature, so they are, commonly used in electrical heating devices., , Copper and aluminium are used for electrical transmission lines as they, have low resistivity., , |], A, , —_, , . _K, HHHH-{+}—, When two or more resistors are connected end to end, the arrangement Is, , called series combination., , e ‘Total/resultant/overall/effective resistance in series, , R =R,+R,+R,, , ¢ Current through each resistor is same., , Y, , Y, , Total voltage = Sum of voltage drops, , Voltage across each resistor :, , V=V,+V,+V,, V,=IR,, V,=IR,, V,=IR,, , V=IR, + IR, +IR,, IR=I(R, +R, +R,), R=R, +R, +R,, , Equivalent resistance is larger than the largest individual resistance., , [V,+V,+V,=V], V=IR, , Scanne d with CamScanner
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Resistors in Parallel :, , , , , , , , , ®, wt, HHH) Oe, , ¢ Voltage across each resistor is same and equal to the applied voltage., , , , ¢ Total current is equal to sum of currents through the individual reistances., , , , Slat +,, Vv ss Ms V, R oR RD R,, ¢ Reciprocal of equivalent resistance 1s equal to sum of reciprocals of individual, resistances. | a |, R, R, R, R,, , ¢ Equivalent resistance Is less than the value of the smallest individual resistance, in the combination., , Advantages of Parallel Combination over Series Combination, , (1) In series circuit, when one component fails, the circuit is broken and none of, the component works., , (11) Different appliances have different requirement of current. This cannot be, satisfied in series as Current remains same., , (111) The total resistance in a parallel circuit is decreased., Heating Effect of Electric Circuit, , If an electric circuit 1s purely resistive, the source of energy continually get, dissipated entirely in form of heat. This is known as heating effect of electric, , current., As E=PxT => Vit {E=H}, Heat produced, H = VI¢ {V =IR}, Or Heat produced, H = I?R¢, , Joule’s Law of Heating Effect of Electric Current, , It states that the heat produced in a resistor is, , Scanne d with CamScanner
