Investigating The Factors Which Affect The Resistance

Of A Wire Essay, Research Paper

Background KnowledgeRESISTANCEElectrons move more

easily through some conductors when a potential difference is applied.

Resistance is determined by how good or bad a conductor a material is. A good conductor has a

low resistance while a poor conductor has a high resistance.THE OHMResistance is defined by: R= V/I????????????????? ????????????????????????????????????????????????????????????????????????????????????????????????????????? If

I= 2A when V= 12v, then R= 12/2?? =????? 6 ΩRESISTORSSome

conductors are made from carbon or alloy wires, and are intended to have

resistance, so we call them resistors. Resistors used in everyday life have

values ranging form usually a few ohms, but go up to millions of ohms.A Resistor:? RESISTORS IN SERIES The

resistors below are in Series. The current flowing through all (I) is the same,

and the separate potential difference across then is the same as the total

potential difference across the 3 (V).i.e.???? V= V1 + V2 + V3????????????????????????????????????????????? V1= IR 1 ??????????????????????????????????????????????????????????????????????? V2=

IR 2 ??????????????????????????????????????????????????????????????????????? V3=

IR 3 If R is the

combined resistance, V= IR So: IR= IR1 + IR2 + IR 3 Dividing both sides by I R= R1 + R2 + R3 ??????????????????????????????????????????????????????????????? RESISTORS IN PARALLEL The

resistors below are parallel. The total current (I) equals the sum of the

currents in the separate branches, and the potential difference between the

ends of each is the same. i.e.?? I= I 1 + I 2 + I 3But:I

1 = V/R1 ??????? I

2= V/R2 ??????? I 3= V/R3Also, if R is the combined Resistance, V=IR. So:V/R = V/R1 + V/R2 + V/R3 Dividing

both sides by V: 1/R = 1/R1 + 1/R2 + 1/R3 Tow

resistors in Parallel: 1/R = 1/R1 + 1/R2 = R2/R1R2 + R1/

R1R2 Therefore: ????? 1/R= R2+R1/R1R2Inverting

both sides:R=

R1R2/R1+R2 = product of resistances/sum of resistancesWAYS OF MEASURING RESISTANCE 1.




TEMPERATURE OF THE WIRE At low temperatures, the atoms in the wire vibrate

less, so it easier for the electrons to pass through because of the low

resistance. At high temperatures, the

atoms vibrate more, offering more resistance and making it harder for the

electrons to pass through. PREDICTION I predict that the longer the wire, the higher the

resistance.??????????????????????????????????????????????????? ??????????? ??? i.e.?????????? Resistance

? ∝? Length ??? This is because the wire acts like

a series of resistors, whci restrict the flow of electricity. Therefore, the

longer the wire, the more the electricity is restricted over the distance. APPARATUS ????? PLAN1. I

will measure the resistance of 8 different lengths of nickel-chrome wire using

the ammeter-voltmeter method. 2. For

the first length, which will be 10cm, I will measure the current going through

the wire and then I will measure the voltage across the 10cm of wire. 3. I

will then find the resistance of the wire using Ohm?s Law, where I will have to

divide the obtained voltage by the current reading to get the resistance. 4. I

will repeat the above process for all the lengths of wire, ranging from 10cm to

80cm. 5. I

will repeat the whole process to prevent any errors. I will take all the

readings again staring this time at 80cm and working my way back. 6. Because

I will have two measurements for the resistance of each length of wire, I will

find the average of these two readings. 7. I will

record all the results in a table like the one below. 8. I will

use a multimeter as an Ohmmeter just to check the resistance in case of any

miscalculation. Length (m) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 First Voltage (V) First Current (A) First Resistance (Ω) Second Voltage (V) Second Current (A) Second Resistance (Ω) Average Resistance (Ω) Ohm-meter Reading (Ω) SAFETY I will ensure that none of the wires are frayed and

that there is no water near any electric equipment; as in all electrical

experiments.HANDLING RESULTS I will draw a graph of

Resistance against Length of wire with Resistance on the Y-axis and Length on

the X-axis.Resistance

(Ω) ??????????????????????????????????????????????? If

my prediction is right, ??????????????????????????????????? The graph should show a ??????????????????????????????????? Straight line through the

origin. ???????????????????????????? Length (m) AT THIS POINT IN MY INVESTIGATION I CARRIED OUT THE


set up the equipment as shown below. 2. I

connected the multimeter in series with a D.C. power supply, setting the value

to 4V. The multimeter was better to use because of the larger currents and

because the readings are given to 2 decimal places. 3. I

connected a one metre length of nickel-chrome wire which was taped a metre

ruler to he output from the ammeter. 4. I

then connected the voltmeter across the wire I was testing. 5. I

connected the negative terminal of the voltmeter to the negative terminal of

the power supply, therefore completing the circuit. 6. 10

cm of wire were stepped off by the voltmeter leads and I recorded the readings

of voltage and current. 7. I

repeated the above process from 10cm to 80cm in steps of 10 8. Because

the shorter lengths of wire became quite hot, the readings were taken quickly,

but I allowed the wire to cool down before the next reading. 9. I

repeated the whole experiment again, this time starting off at the 80cm mark

and working my way back to 10cm in steps of 10cm. 10.

I then checked my readings with the multimeter we used in the

experiment as an Ohmmeter. I recorded the resistances for each length of wire

after the wire had been disconnected from the circuit. APPARATUS USED: ???????


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