The resistance of an ohmic conductor therefore does not change when
the voltage does. Method: Diagram: The equipment needed consists of: Key:
Ordinary wires Switch putty A power pack Ammeter variable resistor ammeter
Voltmeter 2 crocodile clips battery cell putty 2 one penny coins voltmeter
variable resistor The apparatus was set up as shown on the diagram. 20cm of
putty was fixed between P and Q, with a one-penny coin at both ends, using
crocodile clips. An asbestos mat was placed underneath the wire for safety. The
current flowing through the wire was recorded to the nearest 0.01A using an
ammeter placed in series, in the circuit.
The voltage across the wire was
measured to the nearest 0.01V using a voltmeter placed in parallel, across the
wire. The cell terminals were then reserved so that the current would flow in
the opposite direction and the readings of V and I, were again taken, then
recorded to give repeat readings. The 2 readings for current or I were averaged,
and the 2 readings for V or voltage were averaged. The resistance was the
calculated using the formula; R=V / I The length of the putty was recorded. The
putty was 20cm to start off with, and 2cm were then cut off after each reading.
The experiment was repeated 10 times. Each time 2cm was cut off, the current
through the wire and the voltage across the wire changed. The new readings of
the current and voltage were taken, repeated the averaged as before, and R was
calculated. As mentioned before, the experiment was repeated 10 times
altogether, shorting the wire 2cm each time, to give a range of 20cm to 2cm.
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