14. You are given a copper bar of dimensions 1cm x 3 cm x 6 cm and asked to atta

Question

14. You are given a copper bar of dimensions 1cm x 3 cm x 6 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the smallest possible resistance, you should attach the leads to the opposite faces that measure a. 3 cm x 6 cm. b, 1 cm × 3 cm. c, 1 cm × 6 cm. d. Any pair of faces produces the same resistance. 15. The potential difference between the ends of a resistor is 20 V when a current of 5 A flows through it. What is the resistance of that resistor? a. 100 b. 15 c. 4 m. 3 x 10-3 m and its length is 6 m, what is its resistance? a. 152

Explanation / Answer

resistance R = rho*L/A

a) R1 = rho*1/(3*6) = rho/18

b) R2 = rho*6/(1*3) = rho*2

c) R3 = rho*3/(1*6) = rho/2

R is smallest

OPTIOn (a) <<<<----------ANSWER

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15)

from ohms law

V = I*R

resistance R = V/I = 20/5 = 4 ohms

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16)

resistance = resistivity*L/A

A = area of cross section = pi*r^2

r = radius = 1.5*10^-3 m

R = 4*10^-8*6/(pi*(1.5*10^-3)^2)

R = 0.034 ohm

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