CURRENT ELECTRICITY PREPARED BY S.ANNASAWMY 4/4/2020 1 CURRENT - - PowerPoint PPT Presentation

GRADE 11

CURRENT ELECTRICITY

4/4/2020 1 PREPARED BY S.ANNASAWMY

CURRENT

Electric current :- is the flow of electrons through a conductor or it can also be defined as the rate

• f

flow

• f

charges through a conductor or the quantity of charges flowing through a conductor in unit time.

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According to the definition

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Current = charge ÷ time

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I = Q ÷ t

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Since unit of charge is Coulomb (C), time is second (s) then unit

• f current is coulomb per

second (C/s)

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S.I unit of current is the Ampere (A)

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1 A= 1 C/s

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Types of current

Conventional current flow

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Conventional current flow gives the direction of electric current taken at the positive terminal of a power supply (cell or battery).

Electron flow

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Electron flow is the opposite of conventional current flow and thus current flows from negative terminal to positive terminal

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Types of current (cont)

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The ammeter

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It is a device used to measure current in an electric circuit.

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Most often it has two terminals, one positive (red) and one negative (black).

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The ammeter is always connected in series with a load or resistor in a circuit.

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Click on link below to understand how an ammeter works

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https://www.bing.com/videos/search?q=ammeter&docid=608049497648398731&m id=1417524BDE1541B3F7E21417524BDE1541B3F7E2&view=detail&FORM=VIRE

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Symbols of electrical components

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Electromotive force (E.m.f)

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Electromotive force of a cell is defined as the energy converted from non-electrical form (chemical) to electrical form when one coulomb of positive charge passes through the cell

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Using the definition

u E.m.f = Work done ÷

Charge

u E = W ÷ Q

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Where W is in Joules (J)

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Q is in Coulombs (C)

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Unit

• f

E.m.f is Joule per Coulomb (J/C)

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S.I unit of E.m.f is the Volt (V)

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Potential difference (P .D)

u Potential

difference is always measured between two points in an electric

• circuit. It is defined as the

amount

• f

energy converted from electrical form to non-electrical form when one coulomb

• f positive charge flows

through the two points.

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Using the definition

u P.D = Workdone ÷ Charge u V = W ÷ Q

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Where W is in Joules (J)

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Q is in Coulombs (C)

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Unit of P.D is Joule per Coulomb (J/C)

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S.I unit of P.D is the Volt (V)

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The volt (V)

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The volt is the S.I unit of elctromotive force, potential difference and voltage.

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In fact the volt can be defined as the potential difference between two points in a conductor if 1 joule of energy is converted from electrical energy to other forms when 1 coulomb of charge flows through the two points.

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1 volt = 1 J/C

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The voltmeter

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To measure the E.m.f and P .D we use a voltmeter.

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Most often it has two terminals,

• ne positive (red) and one negative

(black).

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The ammeter is always connected in parallel with a load or resistor in a circuit.

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Click on link below to understand how an voltmeter works.

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https://www.bing.com/videos/sea rch?q=how+to+read+a+voltmeter &&view=detail&mid=3660ACC935 D7899DEEAA3660ACC935D7899D EEAA&&FORM=VDRVRV

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Measuring EMF and PD using a voltmeter

E.m.f

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To measure the emf of a cell, the positive terminal of the cell is connected to positive terminal of voltmeter and negative terminal

• f cell to negative terminal of

voltmeter.

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Click on link to view how emf is found using a digital voltmeter or a multimeter.

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https://www.bing.com/videos/sear ch?q=how+to+read+a+voltmeter&&v iew=detail&mid=4DDEA388AA110BA 920604DDEA388AA110BA92060&&FO RM=VRDGAR&ru=%2Fvideos%2Fsearc h%3Fq%3Dhow%2Bto%2Bread%2Ba%2 Bvoltmeter%26%26FORM%3DVDVVXX

P .D

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As mentioned earlier voltmeters are connected in parallel to a load when P .D is found.

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Click on the link below to view a video on finding P .D

u https://www.bing.com/videos/

search?q=how+to+read+a+voltm eter&&view=detail&mid=328CD F3F318424095A25328CDF3F3184 24095A25&&FORM=VRDGAR&ru= %2Fvideos%2Fsearch%3Fq%3Dho w%2Bto%2Bread%2Ba%2Bvoltmet er%26%26FORM%3DVDVVXX

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Arrangement of cells

Cells in series

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In series, cells are joined end to end, i.e, positive terminal of one cell is connected to negative terminal of the other cell etc.

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The emf of the battery is given by the sum

• f

the emf’s

• f

the individual cells.

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If E is the overall emf’s of the battery combined with n number cells and E1, E2, E3 , En are the emfs of individual cells.

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Then E = E1 + E2 + E3 + …. + En

Cells in parallel

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In a parallel combination, all the positive terminals are connected together and all the negative terminals are connected together.

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If emf of each cell is identical (E), then the emf of the battery combined is equal to the emf of each cell, i.e, E

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Arrangement of cells (cont)

u Example 1: Suppose we have three cells in series with each

• ther and the emf of cell is 1.5 V. Find the total emf.

u Total emf is E = 1.5 + 1.5 + 1.5 = 4.5 V u Example 2: When the same three cells each of emf 1.5 V are

now connected in parallel. Find the total emf.

u Total emf is E = 1.5 V u Click on the link to view a video based on cells in series and

parallel.

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https://www.bing.com/videos/search?q=cells+in+series+and+parallel&qpv t=cells+in+series+and+parallel&view=detail&mid=6708136C949275602B896 708136C949275602B89&&FORM=VRDGAR&ru=%2Fvideos%2Fsearch%3Fq%3D cells%2Bin%2Bseries%2Band%2Bparallel%26qpvt%3Dcells%2Bin%2Bseries%2Ba nd%2Bparallel%26FORM%3DVDVVXX

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Advantages and disadvantages

• f cells in series

Advantages

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A greater emf is obtained and thus devices that work on such high voltages can be operated.

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Greater current will be obtained from the cells.

Disadvantages

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All cells will get drained out almost at the same time. Thus they all have to be replaced.

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More money has to be spent for replacement of cells.

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Advantages and disadvantages

• f cells in parallel

Advantages

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There is less drain on the cells.

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One cell will get drained up at a

• time. Therefore the arrangement

can be used for a longer period of time.

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Less money spent on replacement as only the cell that has been used up can be replaced.

Disadvantages

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A small emf is obtained although a number of cells have been used.

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Such arrangement cannot be used to operate devices that require high voltages.

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Exercises

Exercises

Exercises

Exercises

Important notice

uPlease send me your work with

your name attached to it through wattsapp on 57888476 or scan the work and send me on my email address rsannasawmy@gmail.com.