Careful Measurement of Emf and or Internal Resistance of a Cell

Topics: Rechargeable battery, Battery, Electrochemistry Pages: 3 (878 words) Published: March 6, 2013
Case study on Internal resistance of chemical cells
Chemical cells
“A chemical cell converts chemical energy into electrical energy. “Most batteries are combined by several chemical cells. “A chemical reaction occurs inside the battery and causes electric current to flow. There are two main types of batteries, which are rechargeable and non-rechargeable.” The application of chemical cells covers wide range in our life. “Batteries are manufactured in many shapes and sizes, from very small ones used in cameras, to those used in cars or even larger ones.” ( from bibliography [1])

(1)A simple pattern of chemical cells:

Internal resistance
“Internal resistance is the resistance in the power supply, such as a cell or generator “. ( from bibliography[6]) It can be calculated as the difference between the e.m.f. (E), which is the origin of voltage in electrical devices, and the potential difference (Vexternal) between the terminals divided by the current being supplied (I),i.e. r=(E- Vexternal)/I, where r is the internal resistance.

(2)a typical circuit of chemical cell. ]
For the whole circuit, the internal resistance is just like an extra resistance of the circuit. When the current moving through the inside of the cell, the resistance inside the cell work the same way to the external resistance, which means it causes the potential drop as well as external resistance. So the higher internal resistance, the lower current can be drawn out of the power supply for the whole circuit and the lower external voltage.

The factors affect the internal resistance
Batteries work because chemical reaction occurs inside the battery that does work on charge moving electrons from the positive to the negative terminal of the battery. “Basiclly, any factor that affects the rate of this chemical reaction will influence the internal resistance.” Generally, the most common factor that influences the rate of a chemical reaction is temperature. “When the...
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