Department of Natural Sciences

Clayton College & State University

 

February 10, 2003

 

Physics 1112 – Quiz 3a

 

 

Name  _____SOLUTION________________________________

 

 

  1. The rod is made of two materials. Both have a square cross section of 3.00 mm on a side. The first material has a resistivity of 4.00 x 10-3 W-m and is 25.0 cm long while the second material has a resistivity of 6.00 x 10-3 W-m and is 40.0 cm long.

    1. What is the resistance between the ends of the rod?

 

R = R1 + R2

 

R1 = r1 L2/ A = (4.00 x 10-3 W-m) (0.250 m) / (0.003 m x 0.003 m) = 111 W

 

R2 = r2 L2 / A = (6.00 x 10-3 W-m) (0.400 m) / (0.003 m x 0.003 m) = 267 W

 

R = 111 W + 267 W = 378 W

 

    1. You connect the rod to a 120-V source of emf. How much energy is dissipated in the rod in one second?

 

P = V2/R = (120 V)2 / (378 W) = 38.1 W

 

E = P DT = (38.1 W) (1.00 s) = 38.1 J