Department of Natural Sciences

Clayton College & State University

 

February 10, 2003

 

Physics 1112 – Quiz 4b

 

 

Name  ____SOLUTION_________________________________

 

 

  1. A block of carbon is 3.00 cm long and has a square cross-sectional area with sides of 0.500 cm. A potential difference of 8.40 V is maintained across its length. The resistivity of carbon is 3500 x 10-8 W-m.

 

    1. What is the resistance of the block?

 

 

R = r L/ A = (3500 x 10-8 W-m) (0.0300 m) / (0.005 m x 0.005 m) = 0.0420 W

 

    1. What is the current in this resistor?

 

I = DV/R = (8.40 V) / (0.0420  W) = 200A

 

 

    1. How much energy is dissipated in the block in one second?

 

P = I DV = (200 A) (8.40 V) = 1680 W

E = P DT = (168 W) (1.00 s) = 1680 J