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in Physics by (64.8k points)

(a) A rectangular carbon block has dimensions 1.0 cm x 1.0 cm x 50 cm.

(i) What is the resistance measured between the two square ends?

(ii) between two opposing rectangular faces / Resistivity of carbon at 20°C is 3.5 X 10-5 Ω-m. 

(b) A current of 5 A exists in a 10-Ω resistance for 4 minutes (i) how many coulombs and (ii) how many electrons pass through any section oftlze resistor in this time? Charge of the electron =1.6 x 10-19 C.

1 Answer

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(a) (i) R = ρl/A

Here, A = 1 x 1cm2= 10-4m2; l = 0.5m

∴ R = 3.5 x 10-5 x 0.5/10-4 = 0.175Ω

(ii) Here, l = 1cm; A = 1 x 50cm2 = 5 x 10-3m2

R = 3.5 x 10-5 x 10-2/5 x 10-3 = 7 x 10-5Ω

(b) (i) Q = It = 5 x (4 x 60) = 1200C

(ii) n = Q/e = 1200/(1.6 x 10-19) = 75 x 1020

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