10 cbse Electricity

1. Electricity
Electricity

2. IMPORTANT POINTS

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. Charge conservation
• electric charges can neither be created nor
destroyed but can be transferred from one
body to another

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. Conductors
• Substance in which charges can flow freely are
called conductors.
• Here electrons are loosely bound with the
nucleus.

8. AC and DC
• Current may be direct, varying or alternating
current

9. • Direct current (DC)

10. • Alternating current(AC)

12. Voltmeter
• Used to find potential difference between two
points
• Should be connected in parallel
• symbol
VV

13. Ammeter
• Used to find current in a closed circuits
• Should be connected in series
• symbol
AA

14. Galvanometer
• Used to detect current in a circuit
• Should be connected in series
• symbol
AG

15. 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

16. • Graphically it can be shown:

17. 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.

18. Resistance
• The opposition caused to the flow of current
• It is denoted by the symbol

19. Factors affecting resistance
• Resistivity
• Length of the wire (R ᾳ l)
• The Area of cross section (Rᾳ1/A)
• So R=ῤl/A

20. 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)

21. Resistor
• It is the device used to offer resistance in a
circuit

22. Rheostat
• It is a variable resistor
• It is connected in series

23. Combinations of resistors
• Resistors in series
• Resistors in parallel

24. 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

25. 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

26. 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

27. 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

28. • 1kW=1000watts
• 1MW=1000000Watts
• 1hp (horse power)=746watts

29. Kilowatt hour
• It is the commercial unit for electrical energy
• 1kWh=1000Wh=1000xJ/sx3600seconds
=3600000J

30. 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

31. Tungsten filament in bulbs
• High resistivity
• High melting point(3380˚C)

32. 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

33. • 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