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# Careful Measurement of Emf and or Internal Resistance of a Cell Essay Sample

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## Careful Measurement of Emf and or Internal Resistance of a Cell Essay Sample

“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 temperature is higher, the reactants are moving faster and can interact more quickly.” In general, higher temperatures imply faster reaction rates, which indicate that more active electrons are, therefore, lower internal resistance. “Other factors that affect the internal resistance include: size of the electrodes, the distance between the electrodes, concentration of the reactants, concentration of the products, nature of the electrochemical reactions, etc.”( from Bibliography [2])

The application of chemical cells
NiCd Batteries
“Nickel-Cadmium (NiCd) is a very well-known rechargeable battery technology, used by several electronic equipments, such as laptop, computers, cell phones etc. As the name implies, NiCd batteries are a kind of chemical cell, which made of two chemical elements, Nickel, under the form of Nickelic Hydroxide, and Cadmium, which has very low internal resistance. It is also very well known by its famous “memory effect”, which makes the kind of battery to lose its charge faster when it is old than when it was brand new”. ( from bibliography[7])

Although it has very low internal resistance [i.e. low voltage drop at high current draw], the low internal resistance can be a disadvantage, in that if the battery is shorted it can get dangerously hot very quickly, which may cause a big fire accidently.

How do batteries (combination of several cells) affect the environment
Chemical cells always have heavy metals inside which are bad for the environment, just as they are bad for humans. All of those metals are poisonous and can cause problems in animals just like they do to humans. For example, the following lists 2 kinds of heavy metals inside chemical cell. “Mercury is incredibly poisonous, which leads brain developing problems and nickel in comparison is less harmful but that does not mean it doesn’t hurt the environment. When batteries are simply thrown in landfills, these metals leach into ground water and into the environment.” ( from Bibliography [4])

Therefore, we set a particular rubbish bin for cells, which can intensively recycle the used batteries and reduce the harm to the society. Apart from this, I also recommend several ways to protect environment. “1. Buy batteries that have less mercury and heavy metals.2. Try to not buy more batteries when you already have enough battery on hand.3. Consider using of rechargeable batteries.” ( from Bibliography [5])

The practical of determining an alkaline cell’s internal resistance requires knowledge of identifying independent and dependent variables as well as control variables. From the information I have researched, I got a better understanding of the different variables which may affect the result in the practical, and therefore, by applying these knowledge, may results will be more valid and consistent.

Bibliography:
Web site

[1]Copied from: http://simple.wikipedia.org/wiki/Chemical_cell
Pictures from: (1)http://chemwiki.ucdavis.edu/@api/deki/files/736/=chemical_cell_(1).jpg
[2]Copy from: http://en.allexperts.com/q/Physics-1358/2008/12/internal-resistance-battery.htm
[5]Copied from: http://www.squidoo.com/recycle-battery
Book
[6]Copied from: Oxford Dictionary of Physics Publisher: Oxford University Press, USA
Publication Date: 2005 ISBN: 0192806289 P249
Journal
[7]Copied from: Article The Truth About NICD Batteries Author: Gabriel Torres
All copied at 3/3/2013

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