Electric Currents & Ohm's Law - Units of Resistivity example 3
Question : (a) A rectangular carbon block has dimensions 1.0 cm × 1.0 cm × 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 × 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 of the resistor in this time ? Charge of the electron
= 1.6 × 10−19 C.
Solution :
(a) A rectangular carbon block has dimensions 1.0 cm × 1.0 cm × 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 × 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 of the resistor in this time ? Charge of the electron = 1.6 × 10−19 C.
(b) (i) Q = It = 5 × (4 × 60) = 1200 C
(ii) n = Q/e = 1200 / 1.6 x 10-19
= 75 x 1020
Read article – Units of Resistivity
Visit NCERTworld.com for NCERT solutions and Textbook downloads