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InterviewSolution
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Describe a simple experiment to demonstrate variation of resistance on (i) length (ii) Cross section area and (iii) material of the conductor. What are the conclusions drawn? |
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Answer» Solution :To demonstrate dependence of resistance on length, cross section area and material of the conductor we complete an electric circuit as shown in fig 12.25. (i) EFFECTIVE of length: Take the resistance wire number 1 of length l and connect, it in the circuit. Put plug in key K and note ammeter reading `I_1`. Now instead of wire number 1, connect wire number 2 of double length but of same material and same thickness. As before note ammeter reading `I_2`. Experimentally it is observed `I_2=I_1/2` It shows that resistance of 2nd wire is double of 1st wire. Thus, we conclude that `R_2/R_1=l_2/l_1=(2l)/l=2 or R prop 1` (ii) Effect of cross section area: Replace the wire by resistance wire number 3 of length l but the thickness more than wire number 1. Put plug in key and note ammeter reading `l_3`. It is more than `I_1`. It means for a thicker wire (i.e., a wire of greater cross sectional area) the resistance is less. EXACT calculations SHOW that resistance is inversely proportional to cross section area of the conductor. Thus, `R prop 1/A` (iii) Effect of material: Now,take a wire number 4 of some other material but of length l and same thickness as wire number 1. Connect the wire in the circuit and again note ammeter reading `I_4`. We find that `I_4` is different from `I_1`. It shows that resistance depends on material of the conductor. 
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