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Rev. Notes > IGCSE > Elecrical Quantities
Previous Topic Elecrical Quantities Next Topic

Electric charge One Coulomb Charge Production of electric charge
Detection of electric charge Experiment to detect the electric charge Electrical conductors and insulators
Electric field Electrostatic forces Application of electrostatic forces
Electric current One Ampere of electric current Direction of electric current
Basic relation of electric current Direct current Alternating current
Ammeter Electromotive force - (e.m.f.) Potential difference
One Volt Explanation of potential difference Measurement of potential difference
Voltmeter Resistance Affect of length of the conductor on resistance
Affect of cross-sectional area on resistance Affect of temeprature on resistance How nature of material affects the eresistance
Ohm's law Potential difference - Current graph for Ohmic conductors Potential difference - Current graph for tungsten filament
Potential difference - Current graph for semiconductor diode Electrical energy Formula for electrical energy
Electrical Power Formulae for electrical power

Electromotive force - (e.m.f.)

Circuit below shows set up of an electric source of e.m.f. = E volts, driving electric charges round the closed the circuit. The e.m.f. drives the electic chrges through the internal resistance of source as well as the external resistance of the circuit.

Hence if the e.m.f. of the cell is 2 V, the total energy dissipated (given out) is 2 joules when one coulomb of charge flows through the closed circuit. Since energy = charge (Q) X potential difference (V). The energy given out will be in the form of heat and light at the bulb with some heat generated within the cell, and along the connecting wires. If Ohm's law is applied for the whole circuit, we have

E = I (r + R) i.e. current X total resistance in the whole circuit

Where E is the e.m.f. of the source in volts

I the current flowing through the closed circuit in the lamp

r the internal resistance of the cell in ohm

R the total external resistance in ohm





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View Comments on this Chapter - Total Comments (6)
sree Said :
wish these had a diagrams
  24/12/15 10:01 AM
student 567 Said :
There are no diagrams, but seeing that you don't give a shit... why should i bother to comment?! Can you just put the dam diagram up already!
  18/04/14 08:10 PM
Deepak varun Said :
there is a spelling mistake to say said they said asaid please change it admin
  17/11/13 06:26 AM
gargi sachdev Said :
diagrams aren't there ...
  29/08/12 12:35 AM
gargi sachdev Said :
diagrams aren't there ...
  29/08/12 12:35 AM
Ajay Said :
I cant see any diagrams? can u help me with it
------------------------------------------------------------------------------------- Admin Replied:

Hi Ajay, thank you for informing us about this issue. We will make sure we make those images available for you as soon as possible.

Thank you

  15/03/12 12:13 PM


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