2.2 Analysing the Relationship Between Electric Current and Potential Difference
Transcript of 2.2 Analysing the Relationship Between Electric Current and Potential Difference
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Analysing the Relationship betweenCurrent and Potential Difference
By Ms Nurul Ain Mat Aron
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define potential difference
describe the relationship between current and potential difference
state Ohms law
define resistance
explain factors that affect resistance
solve problems involving potential difference, current and resistance
describe superconductors
Objectives
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Potential Difference, V
The potential difference (or voltage) between two points in a circuitcauses an electric charge to move between the two points
Positive
terminal
Negative
terminal
High potential Low potential
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Potential Difference, V
I I
I I
II
II
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Potential Difference, V
The potential difference (or voltage) between two points is defined
as the work done in moving 1 coulomb of charge from one point to
another.
The SI unit is
volt, V
Energy
produced, E
or
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The energy released between point A and B is 60J when a charge of
20 C flows from A to B.
a) What is the potential difference between A and B?
b) If the time taken for the 20 C to flow between A and B is 40s,what is the value of the current flowing through the bulb?
Problem 1
Potential Difference, V
Answer: 3V and 0.5 A
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How much energy has been transferred when 5 C charges move
across a potential difference of 10V?
Problem 2
Potential Difference, V
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Ohms Law states that the current flowing through an ohmic conductor is
directly proportional to the potential difference across its ends, providedthat its temperature and other physical conditions remain constant.
Ohms Law
V I
The relationship between the current passing through 2 points in aconductor and the potential difference between the 2 points is given by
Ohm's law
Any other conductors, other
than metallic conductors,
which obey Ohms Law
V = IR
where V = potential difference [V]
I = current [A]
R = resistance []
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The resistance, R is defined as the ratio of the potential difference (or
voltage), V across the conductor to the current, I flowing through it.
Resistance, R
A current flows through a conductor when a potential difference is appliedacross it. The current consists of a flow of charges. The charges encounter
resistance from the atoms in the conductor.
Charges encounter resistance when they flow
through a conductor
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What is the current flow through an 800 toaster when it is operating
on 240V?
Problem 3
Ohms Law
Answer: 0.3 A
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A 9 V battery connected across a resistance wire produces a steady
current of 0.3 A through the wire. If the internal resistance of the
battery can be neglected, what is the resistance of the wire?
Problem 4
Ohms Law
Answer: 30 ohm
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Factors Affecting Resistance
The resistance of a wire depends on four factors:
a) length
b) cross-sectional area
c) type of material
d) Temperature
At constant temperature, resistance, R (l/A) where l is the length
and A is the cross sectional area.
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Factors Affecting Resistance
Longer wire - Higher Resistance
Thicker wire - Lower Resistance
Higher temperature - Higher Resistance
The type of material
(copper has resistance lower than iron)
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Superconductors are materials where their electrical resistance isexactly zero at some relatively low temperature.
Superconductor
Presentation1 Magnetic Resonance Imaging (MRI)
2. Magnetic-Levitation Train (MagLev)
3. Electric generators