A View from the Bridge, acts 1 and 2.

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AIM:  THE RESISTIVITY OF CONSTANTAN WIRE

PLANNING

   

The formula for finding the resistivity of a wire is

        Where: R is resistance

                     P is the resistivity

                     A is the cross-sectional area

                     L is the length

The variables involved are the cross-sectional area (A), the length (L), the

Resistance ® and resistivity (P).  The resistivity of every wire is constant

So the changing variables are the resistance (r=v/I) where the resistance is

The dependent variable.   Keep the area constant.    

To calculate how the change in length affects the resistance, we plot a graph

Of length against resistance.  The resistance should be proportional to the

Length, R∝L (prediction) according to Ohms law i.e. there should be an

Increase in the resistance as the length increases- the longer the length, the

Greater the resistance.

DIAGRAM

METHOD:

Set up the circuit as shown in the diagram above, start the experiment by taping

The constantan wire of 100cm the has been measured to the metre rule.  Make

Sure the wire is carefully tightened at both ends of the metre rule then connects

The digital ammeter, and the voltmeter at last (the circuit should be able to

Function without it.) As shown on diagram above.   Switch on the variable power

Supply box.  

Record the voltage and current readings that are displayed on the digital screens

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Of the ammeter and voltmeter respectively.  Repeat the procedure using eight

Different lengths ranging from 10cm to 80 cm.   Then, repeat the same experiment

Two more times to get an average.

CALCULATING THE RESISTANCE

The formula for calculating the resistance is:  Resistance = voltage/current (V/I)

CALCULATING THE AREA

Using a micrometer screw gauge, measure the diameter of the wire at four different

Points and at right angles of each of these points and get an average.  Then calculate the area

With the formula A=πr

Where r is radius=1/2 diameter

A is area

π ...

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