as physics electricity chapter 9

8/20/2019 As Physics Electricity Chapter 9

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ELECTRICITY-Chapter 9

Circuit Symbols

Electric Current

Rate of flow of charge. I = . Q = ItConventionalCurrent.

Current that is regarded to fow rom positive tonegative. i.e. fow o positive charge as it wasearlier known.

Charge Carriers Solis: Electrons Electrolytes! Positive and negative ions

Current and DriftVelocity

I = n"V e# number of electrons er cubic metre! "#cross#section area! V# velocity and e = charge of an electron.

Electromotive$orce%E&$'

(otal wor) done er unit charge flowing round a comlete circuit.

&easured in Volts =

Potential*difference%Voltage'

Energy er unit charge between two oints on a circuit.

&easured In Volts. V =Resistance Ratio of otential difference across a comonent to the current

that flow through it. &easured in +hms% $

Power % = I& or &'

(R or I'

R.

Circuit Symbols

Electric Current

ConventionalCurrent.

Current that is regarded to fow rom positive tonegative. i.e. fow o positive charge as it wasearlier known.

Charge Carriers Solis: Electrons Electrolytes! Positive and negative ions

Current and DriftVelocity

I = n"V e# number of electrons er cubic metre! "#cross#section area! V# velocity and e = charge of an electron.

Electromotive$orce%E&$'

Potential*

difference%Voltage'

Resistance Ratio of otential difference across a comonent to the current

that flow through it. &easured in +hms% $

Power % = I& or &' (R or I'R.


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Current!Is the R"(E of flow of charge

Current is )easure in

"mperes*"$ by ammeter


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Drift velocity of electrons ,ow fast do electrons flow through a wire-

Volume of cylinder = "L

where " is the cross#sectional area of the wire and length /0

If there are n electrons er cubic metre then:

1umber of electrons in cylinder = n"L

If each electron carries charge e then:

Charge carried by electrons in cylinder = n"Le

2ut Current = charge3time = n"/e3t but V=/3t0

4o

I = n"&e or & =


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I = n"V e

1. Calculate the drift velocity in a piece of wire where the current is

1A, the free electron density is 5.0x 1028m- and the diameter of the

wire is 1mm. !ans 5.6758#9 ms#50

2. Calculate the drift velocity of the char"e carriers in a sample of semi

conductor which is 5mm wide and 2mm thic# if the current is 10mA

and the carrier density is $ x 102m-. !58# ms#50

. Calculate the drift velocity of electrons in a sample of copper of

char"e density % $ x 1028 m- which has the same dimensions as the

semi conductor in &uestion 2 and also carries a current of 10mA.

!5.89758#; ms#50


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Conventional current.

+ ,

e#

e#

Current that fows rom positive tonegative or fow o positive charge as itwas earlier known.

Electrons fows in opposite direction-

negative to positive.

"n electron has a charge of: #5.6758#5


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'lectromotive force(e.m.f)

*he electrical ener"y transferred from other forms per Coulom+ of char"e that passes throu"h the +attery source.

*o measure e.m.f connect a voltmeter across the terminals of the +attery

'mf, ' = ’ W=Q

(otal wor) done er unit charge flowing round a

comlete circuit. &easured in Volts


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%TETI"L /I00ERECE.Potential difference ( Voltage) is energy required

per Coulomb of charge to move from one pointto another

P.d across bulb =V " # V2

V = energy = W

Charge = Q

!nits" Volt(V) or

#C$%


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The &oltThe p.. bet1een t1o points i2 one

3oule o2 1or4 is one brin5in5 one

Coulomb o2 char5e 2rom one point to

the other. The hmThe resistance o2 a component 1hen a

potential i22erence o2 6volt rives acurrent o2 6" throu5h the conuctor.


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&'*+& , '&'

In Series the total resistance

is sum o2 all resistors.

R T = R

6

+ R '

+ R 7

R 5

R

R

10

68

R 10


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Calculate(a) the total resistance of the circuits

(b) The current in the circuit. I=V/R

6.8& 6.8&6.8&


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RESIST"CE I %"R"LLEL

R 5R R

In Parallel the total resistance is

1 = 1 + 1

RT R

1 R

2

R2 R


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0in

*a$ the total resistance

*b$ The current 2lo1in5 in the circuit


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0in the total resistance

Ω

9Ω


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:hat is Resistance;

Is the ratio of voltage to currentflowing through a circuit.&easured in ohms%Ω'.


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Electrical Ener5y

Electrical ener5y is ener5y supplie

by 2lo1in5 electric current.

E= volta5e < Char5e =QC = &olta5e < current < time.

E= vIt


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ELECTRIC"L %:ER

Electrical po1er is rate o2 ener5y trans2er.%o1er = = I&

%o1er = volta5e < current

% = I&

%=

%%o1er is measure in :atts or 3(s


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-uses

-use" piece of .ire that .ill melt .hen a current of a certain

si/e passes though it Connected on the live .ire

(he fuse value needs to be >ust above the

normal oerating current

as physics electricity chapter 9

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