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Name: sneha
Status: student
Age: 15
Location: N/A
Country: N/A
Date: 2000-2001


Question:
hi, I'm studying resistance as part of my coursework but i am totally lost as to how to define it and was wondering if you could give me a simple statement that could define it in an understandable and easy manner. the factor i have chosen to investigate is how length can affect resistance-"as the length increases so does the resistance". this is a statement i am working around but i still need help. can you possibly also explain what a variable resistor is?


Replies:
Electrical resistance is proportional to the length of a wire divided by the cross sectional area. If the lenth double then so does the resistanc, if the are doubles then the resistance is half the initial value. The is a proportionality constant known as the electrical resistivity, usually represented by the Greek letter rho (lower case). rho depends on the material of the wire and other variables such as temperature. Hope this is sufficient to solve your problem.

Dr. Harold Myron


"Resistance" is a resistance to the flow of current through a part of a circuit. Two important concepts are energy and charge. As charge flows through a standard material, some of the energy in the moving charge is lost to the structure of the material as heat. For many materials, the voltage drop across the material is proportional to the resulting current through the material. The ratio of these values, (voltage drop across material)/(current through material), is the resistance. A larger resistance results in a smaller current.

Now for why resistance of a material is proportional to its length. Suppose one volt will get one ampere of current through 1 cm of material. Resistance is (1V)/(1A) = 1 Ohm. A 3 cm piece of material will be like three 1 cm pieces connected end-to-end. Assume one ampere is flowing through. A potential drop of 1 volt is necessary across the first centimeter. A drop of 1 V is necessary across the second, and again across the third. Any charge that passes through all three has its potential decrease by a total of 3 volts. Resistance of the entire 3 centimeters is (3V)/(1A) = 3 Ohms. As length increases, so does resistance.

A variable resistor is a long resistor that can be adjusted. The connection at one end is stationary. The other connection can be moved to various points on the apparatus, altering the length of resistor that current actually passes through. When the current doesn't have to pass through as great a length, the resistance decreases.

Kenneth Mellendorf



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