GRADE 11 CURRENT ELECTRICITY PREPARED BY S.ANNASAWMY 4/4/2020 1
CURRENT According to the definition u Current = charge ÷ time u I = Q ÷ t u Electric current :- is the flow of Since unit of charge is Coulomb electrons through a conductor or u (C), time is second (s) then unit it can also be defined as the rate of current is coulomb per of flow of charges through second (C/s) a conductor or the quantity of charges flowing through a S.I unit of current is the Ampere u conductor in unit time. (A) u 1 A= 1 C/s u PREPARED BY S.ANNASAWMY 4/4/2020 2
Types of current Electron flow Conventional current flow Conventional current flow gives Electron flow is the opposite of u u the direction of electric current conventional current flow and thus taken at the positive terminal of a current flows from negative power supply (cell or battery). terminal to positive terminal PREPARED BY S.ANNASAWMY 4/4/2020 3
Types of current (cont) PREPARED BY S.ANNASAWMY 4/4/2020 4
The ammeter It is a device used to measure current in an electric circuit. u Most often it has two terminals, one positive (red) and one negative (black). u The ammeter is always connected in series with a load or resistor in a circuit. u Click on link below to understand how an ammeter works u https://www.bing.com/videos/search?q=ammeter&docid=608049497648398731&m u id=1417524BDE1541B3F7E21417524BDE1541B3F7E2&view=detail&FORM=VIRE PREPARED BY S.ANNASAWMY 4/4/2020 5
Symbols of electrical components PREPARED BY S.ANNASAWMY 4/4/2020 6
Electromotive force (E.m.f) Electromotive force of a cell is Using the definition u u defined as the energy converted from non-electrical form (chemical) to electrical form u E.m.f = Work done ÷ when one coulomb of positive Charge charge passes through the cell u E = W ÷ Q Where W is in Joules (J) u Q is in Coulombs (C) u Unit of E.m.f is Joule per u Coulomb (J/C) S.I unit of E.m.f is the Volt (V) u PREPARED BY S.ANNASAWMY 4/4/2020 7
Potential difference (P .D) Using the definition u Potential difference is u always measured between u P.D = Workdone ÷ Charge two points in an electric u V = W ÷ Q circuit. It is defined as the Where W is in Joules (J) u amount of energy Q is in Coulombs (C) converted from electrical u Unit of P.D is Joule per Coulomb form to non-electrical u (J/C) form when one coulomb S.I unit of P.D is the Volt (V) u of positive charge flows through the two points. PREPARED BY S.ANNASAWMY 4/4/2020 8
The volt (V) The volt is the S.I unit of elctromotive force, potential difference and u voltage. In fact the volt can be defined as the potential difference between two u 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. 1 volt = 1 J/C u PREPARED BY S.ANNASAWMY 4/4/2020 9
The voltmeter To measure the E.m.f and P .D we Click on link below to understand u u use a voltmeter . how an voltmeter works. Most often it has two terminals, https://www.bing.com/videos/sea u u one positive (red) and one negative rch?q=how+to+read+a+voltmeter (black). &&view=detail&mid=3660ACC935 D7899DEEAA3660ACC935D7899D The ammeter is always connected u EEAA&&FORM=VDRVRV in parallel with a load or resistor in a circuit. PREPARED BY S.ANNASAWMY 4/4/2020 10
Measuring EMF and PD using a voltmeter E.m.f P .D To measure the emf of a cell, the As mentioned earlier voltmeters u u positive terminal of the cell is are connected in parallel to a connected to positive terminal of load when P .D is found. voltmeter and negative terminal Click on the link below to view a of cell to negative terminal of u voltmeter. video on finding P .D Click on link to view how emf is u https://www.bing.com/videos/ u found using a digital voltmeter or search?q=how+to+read+a+voltm a multimeter. eter&&view=detail&mid=328CD https://www.bing.com/videos/sear u F3F318424095A25328CDF3F3184 ch?q=how+to+read+a+voltmeter&&v 24095A25&&FORM=VRDGAR&ru= iew=detail&mid=4DDEA388AA110BA %2Fvideos%2Fsearch%3Fq%3Dho 920604DDEA388AA110BA92060&&FO w%2Bto%2Bread%2Ba%2Bvoltmet RM=VRDGAR&ru=%2Fvideos%2Fsearc h%3Fq%3Dhow%2Bto%2Bread%2Ba%2 er%26%26FORM%3DVDVVXX Bvoltmeter%26%26FORM%3DVDVVXX PREPARED BY S.ANNASAWMY 4/4/2020 11
Arrangement of cells Cells in series Cells in parallel In series, cells are joined end to In a parallel combination, all the u u end, i.e, positive terminal of one positive terminals are connected cell is connected to negative together and all the negative terminal of the other cell etc. terminals are connected together. The emf of the battery is given by If emf of each cell is identical u u the sum of the emf’s of the (E), then the emf of the battery individual cells. combined is equal to the emf of each cell, i.e, E If E is the overall emf’s of the u battery combined with n number cells and E 1, E 2, E 3 , E n are the emfs of individual cells. Then E = E 1 + E 2 + E 3 + …. + E n u PREPARED BY S.ANNASAWMY 4/4/2020 12
Arrangement of cells (cont) u Example 1: Suppose we have three cells in series with each other 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. https://www.bing.com/videos/search?q=cells+in+series+and+parallel&qpv u 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 PREPARED BY S.ANNASAWMY 4/4/2020 13
Advantages and disadvantages of cells in series Advantages Disadvantages A greater emf is obtained and thus All cells will get drained out almost u u devices that work on such high at the same time. Thus they all voltages can be operated. have to be replaced. Greater current will be obtained More money has to be spent for u u from the cells. replacement of cells. PREPARED BY S.ANNASAWMY 4/4/2020 14
Advantages and disadvantages of cells in parallel Advantages Disadvantages There is less drain on the cells. A small emf is obtained although a u u number of cells have been used. One cell will get drained up at a u time. Therefore the arrangement Such arrangement cannot be used u can be used for a longer period of to operate devices that require time. high voltages. Less money spent on replacement u as only the cell that has been used up can be replaced. PREPARED BY S.ANNASAWMY 4/4/2020 15
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