Page 189 - WCS - Electrical
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WORKSHOP CALCULATION & SCIENCE - CITS
then I = Q/t Q = I x t
The SI unit of current is coulomb. Coulomb is equivalent to the charge contained in nearly 6.24 x 1018 electrons.
Coulomb
In an electric circuit if one Ampere of current passes in one second, then it is called one coulomb. It is also called
ampere second (As). Its larger unit is ampere hour (AH)
1 AH = 3600 As (or) 3600 coulomb
Electro motive force (EMF)
It is the force which causes to flow the free electrons in any closed circuit due to difference in electrical pressure
or potential. It is represented by ‘E.’ Its unit is Volt.
Potential difference (P.D)
This is the difference in electrical potential measured across two points of the circuit. Potential difference is
always less than EMF. The supply voltage is called potential difference. It is represented by V.
Voltage
It is the electric potential between two lines or phase and neutral. Its unit is volt. Voltmeter is used to measure
voltage and it is connected parallel between the supply terminals.
Volt
It is defined as when a current of 1 ampere flows through a resistance of 1 ohm, it is said to have potential
difference of 1 volt.
Current
It is the flow of electrons in any conductor is called current. It is represented by I and its unit is Ampere. Ammeter
is used to measure the current by connecting series with the circuit.
Ampere
When 6.24 x 1018 electrons flow in one second across any cross section of any conductor, the current in it is one
ampere.(or) If the potential difference across the two ends of a conductor is 1 volt and the resistance of conductor
is 1 ohm then the current through is 1 ampere. Ohm 4 depends on the temperature of the conductor
Resistance If the potential difference across the two ends of conductor 1 L L
is 1 volt and the current through it is 1 ampere, then the
It is the property of a substance to oppose to the flow of electric current through it, is called resistance. Symbol: R α L ; R α A ; R α A ; R = ρ A
resistance of the conductor is 1 Ohm.
R, Unit : Ohm (W), Ohm meter is used to measure the resistance.
Specific resistance
Ohm Laws of resistance
The specific resistance of a material is the resistance
If the potential difference across the two ends of conductor is 1 volt and the current through it is 1 ampere, then offered to a current it passed between the opposite faces
The resistance offered by conductor depends on the
the resistance of the conductor is 1 Ohm. following factors. of the unit cube of the material. Specific resistance is
Laws of resistance The resistance of the conductor measured in Ohm - m or micro ohm - cm.
1 is directly proportional to the length of the conductor
The resistance offered by conductor depends on the following factors. Each mateiral has its own specific resistance or
(R L) resistivity.
The resistance of the conductor
2 Varies inversely proportional to its cross sectional area E.g. : Copper - 1.72 cm, Silver - 1.64 cm,
1 is directly proportional to the length of the conductor (R α L) Eureka - 38.5 cm, Iron - 9.8 cm,
1
⎛
2 Varies inversely proportional to its cross sectional area of the conductor ⎜ R α A ⎞ ⎟ ⎠ Aluminium - 2.8 cm, Nickel - 7.8 cm.
of the conductor
⎝
3 Depends on the material with which it is made.
3 Depends on the material with which it is made. ρl
4 depends on the temperature of the conductor
Ohm 4 depends on the temperature of the conductor R= A ohm cm
If the potential difference across the two ends of conductor 1 L L R = Resistance in ohms
is 1 volt and the current through it is 1 ampere, then the R α L ; R α A ; R α A ; R = ρ A
resistance of the conductor is 1 Ohm. l = Length of the conductor in cm
Specific resistance
Laws of resistance r = Specific Resistance in ohm cm
The specific resistance of a material is the resistance
The resistance offered by conductor depends on the offered to a current it passed between the opposite faces (symbol pronounced as rho)
following factors. of the unit cube of the material. Specific resistance is A = Area of cross - section in cm 2
The resistance of the conductor measured in Ohm - m or micro ohm - cm. 176
1 is directly proportional to the length of the conductor Each mateiral has its own specific resistance or
(R L) resistivity. CITS : WCS - Electrical - Exercise 18
2 Varies inversely proportional to its cross sectional area E.g. : Copper - 1.72 cm, Silver - 1.64 cm,
⎛ 1 ⎞ Eureka - 38.5 cm, Iron - 9.8 cm,
of the conductor ⎜ R α ⎟ Aluminium - 2.8 cm, Nickel - 7.8 cm.
⎝ A ⎠
3 Depends on the material with which it is made. ρl
R= ohm cm
A
R = Resistance in ohms
l = Length of the conductor in cm
r = Specific Resistance in ohm cm
(symbol pronounced as rho)
A = Area of cross - section in cm 2
100 Workshop Calculation & Science : (NSQF) Exercise 1.7.33
100 Workshop Calculation & Science : (NSQF) Exercise 1.7.33
