2.2 analysing the relationship between electric current and potential difference

8/11/2019 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


2/14

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

e-

e-

e-

e-

e- e-

e-e-e-

e-

e-

e-

e- e-


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I I

I I

II

II


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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


6/14

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


Answer: 3V and 0.5 A


7/14

How much energy has been transferred when 5 C charges move

across a potential difference of 10V?

Problem 2



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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 []


9/14

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

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2.2 analysing the relationship between electric current and potential difference

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