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# Electricity

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10 cbse Electricity

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### Electricity

1. 1. Electricity Electricity
2. 2. IMPORTANT POINTS
3. 3. PROPERTIES OF CHARGES • There are two types of charges positive and negative • Like charges repel each other and unlike charges attract each other • Charges are quantized(with fixed amount of charge) • Magnitude of every charge is 1.6x10¯¹⁹C
4. 4. Charge conservation • electric charges can neither be created nor destroyed but can be transferred from one body to another
5. 5. Insulators • Insulators do not conduct charges, as electrons are tightly bound with the nucleus. • Insulators can be charged easily by friction.the charges remain localized in them
6. 6. Conductors • Substance in which charges can flow freely are called conductors. • Here electrons are loosely bound with the nucleus.
7. 7. AC and DC • Current may be direct, varying or alternating current
8. 8. • Direct current (DC)
9. 9. • Alternating current(AC)
10. 10. Voltmeter • Used to find potential difference between two points • Should be connected in parallel • symbol VV
11. 11. Ammeter • Used to find current in a closed circuits • Should be connected in series • symbol AA
12. 12. Galvanometer • Used to detect current in a circuit • Should be connected in series • symbol AG
13. 13. Ohm’s law • At constant temperature and pressure the current flowing through a wire is directly proportional to the potential difference across its ends. • V ᾳ I • Or V=IR where R is the resistance
14. 14. • Graphically it can be shown:
15. 15. One Ohm • Resistance offered by wire carrying 1A of current 1V is applied across its ends • Ohm(ᾨ) is unit of resistance • It is in honour of the German physicist George Simon Ohm.
16. 16. Resistance • The opposition caused to the flow of current • It is denoted by the symbol
17. 17. Factors affecting resistance • Resistivity • Length of the wire (R ᾳ l) • The Area of cross section (Rᾳ1/A) • So R=ῤl/A
18. 18. Resistivity(ῤ) • The resistance offered by a wire of unit ength and unit area of cross section • Its unit is ohm-metre(Ω-m) • The reciprocal of resistivity is conductivity • Unit of conductivity mho metre(ʊ-m)
19. 19. Resistor • It is the device used to offer resistance in a circuit
20. 20. Rheostat • It is a variable resistor • It is connected in series
21. 21. Combinations of resistors • Resistors in series • Resistors in parallel
22. 22. Resistors in series • When resistors placed in series the current through them will be the same • The total the potential difference is the algebraic sum of all P.D • V=V1+V2+V3 • The equivalent resistance is the sum of individual resistances • R=R1+R2+R3
23. 23. Resistors in parallel • The potential difference across their ends is the same • The sum of the current through them is the current drawn from the main source of energy • The equivalent resistance is found by 1/R=1/R1+1/R2+1/R3
24. 24. Joule’s law of heating • When a current I flows through a conductor ,heat is produced. The produced is directly proportional to the product of square of current, resistance and the time. • H=I²Rt Other equations • H=(V²/R)t • H=IVt
25. 25. Electric power • The rate at which electric energy is consumed • Power P=W/t=H/t=I²Rt/t=I²R Other eqns • P=VI • P=V²/R • Unit is Watt
26. 26. • 1kW=1000watts • 1MW=1000000Watts • 1hp (horse power)=746watts
27. 27. Kilowatt hour • It is the commercial unit for electrical energy • 1kWh=1000Wh=1000xJ/sx3600seconds =3600000J
28. 28. Calculation of power in daily life situation • Number of units of electricity consumed=No.kWh=total (wattsxhours)/1000 • Total unit of electricity consumed in a month=No.of unitsxNo.of days in month • Total cost of electricity =total units x cost per unit of electricity
29. 29. Tungsten filament in bulbs • High resistivity • High melting point(3380˚C)
30. 30. Fuse wire • The wire which melts, breaks the circuits and prevents the damage of various appliances in house hold connections • It is connected in series with the live wire • It is made up of Lead(Pb) and Tin(Sn) • It is generally encased in a cartridge of porcelain material
31. 31. • Material ρ (Ω•m) at 20 °C Resistivity σ (S/m) at 20 °C Conductivity Silver 1.59×10−8 6.30×107 Copper 1.68×10−8 5.96×107 Annealed copper 1.72×10−8 5.80×107 • Gold 2.44×10−8 4.10×107 • Aluminum 2.82×10−8 3.5×107 • Calcium 3.36×10−8 2.98×107 Tungsten 5.60×10−8 1.79×107 Zinc 5.90×10−8 1.69×107 Nickel 6.99×10−8 1.43×107 Lithium 9.28×10−8 1.08×107 Iron 1.0×10−7 1.00×107 Platinum 1.06×10−7 9.43×106 Tin 1.09×10−7 9.17×106 Carbon steel (1010) 1.43×10−7 Lead 2.2×10−7 4.55×106 Titanium 4.20×10−7 2.38×106 Grain oriented electrical steel 4.60×10−7 2.17×106 Manganin 4.82×10−7 2.07×106 Constantan 4.9×10−7 2.04×106 Stainless steel 6.9×10−7 1.45×106 Mercury 9.8×10−7 1.02×106 Nichrome 1.10×10−6 9.09×105 GaAs 5×10−7 to 10×10−3 5×10−8 to 103 Carbon (amorphous) 5×10−4 to 8×10−4 1.25 to 2×103 Carbon (graphite) 2.5×10−6 to 5.0×10−6 //basal plane 3.0×10−3 ⊥basal plane 2 to 3×105 //basal plane 3.3×102 ⊥basal plane Carbon (diamond) 1×1012 ~10−13