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7.3 Potential D
ShahidMukhlisPhysics Form5
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Electrical Potential
The electric potential V at a
point in an electric field isthe work done to bring aunit ( 1 Coulomb) positive
charge from infinity to thepoint.
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Potential Difference
(Voltage)
The potential difference (p.d.)
between two points is definedas the energy converted fromelectrical to other forms whenone coulomb of positivecharge passes between thetwo points.
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Unit of Potential Difference
The SI unit of potential difference isthe same as that for e.m.f., i.e. thevolt. We define the volt as follows:
The potential difference (p.d.)between two points in a conductor is 1
volt if 1 joule of energy is convertedfrom electrical to other forms when 1coulomb of positive charge flowsthrough it.
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Formula of Potential
Difference
E
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Examp e
How much energy had been transfer when
5 C charges moved across a potentialdifference of 10V?
Answer:
The charge, Q = 5C
Potential difference, V = 10V
Energy, E = ?
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Ohm's Law
The current flowing in the
metallic conductor is directlyproportional to the potentialdifference applied across itsends, provided that the physicalconditions ( such as
temperature ) are constant.
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Formula
Any other conductors, other than
metallic conductors, which obey OhmsLaw are described as Ohmicconductors.
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What is the current through an 8 toaster when itis operating on 240V?
Answer:
(In this question, 2 physical quantities are
given, they are the "240V" and "80". Thequestion doesn't tell what quantites they are.However we can recognise these quantitiesfrom its unit. is the unit of resistance
whereas V is the unit of potential difference.)
Resistance, R = 80
Potential difference, V = 240V=
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Resistance
The resistance R of a material is defined as the ratio V: I,
whereV
is the potential difference across thematerial and Iis the current flowing in it.
Unit:The SI unit of resistance is the ohm (). One ohm is the resistance of amaterial through which a current of one ampere flows when a potentialdifference of one volt is maintained.
R i ti it
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Resistivity
The resistance R of a given conductor
depends on the:length l,
Longer wire - Higher Resistance
cross-sectional area A,Thicker wire - Lower Resistance
temperatureHigher temperature - Higher
Resistance
the type of materialcopper has resistance lower than iron
S d t
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Superconductor
Superconductors are materials where
their electrical resistance is exactlyzero at some relatively lowtemperature.
Application of Superconductor
1. Magnetic Resonance Imaging (MRI)
2. Magnetic-Levitation Train (MagLev)3. Electric generators
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