Physics 212 Question Bank III 2011 Part II Problems A strip of potassium 2.0 cm

Question

Physics 212 Question Bank III 2011 Part II Problems A strip of potassium 2.0 cm wide and Imm thick carrying a current of 100 A produces a Hall emf with magnitude 223 v in a magnetic field of 5.00 T. (a) What is the density n of free electrons in potassium? (b) What is the magnitude of the drift velocity of the electrons? If the magnetic field is then decreased to 2.50 T (c) What is the Hall emf? (d) What is the density n of free electrons in potassium? rrelrrating potential of 80 kV (of appropriate polarity for positive or

Explanation / Answer

given

w = 2 cm = 0.02 m

t = 1mm = 0.001 m

i = 100 A

Vh = 223*10^-6 V

B = 5 T

a. Vh = i*B/n*e*t

e = 1.6*10^-19 C

hence

n = 1.4013*10^28 electrons / m^3

b. vd = i/n*e*A = i/n*e*w*t

vd = 0.00223 m/s

c. B' = 2.5 T

Vh = i*B/n*e*t

hence Vh = 111.5*10^-6 V

d. n = 1.4013*10^28 electrons / m^3

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