Q# 15 (Past Exam Paper – June 2018 Paper 13 Q30)
A slice of germanium of cross-sectional area 1.0 cm2 carries a current of 56 μA. The number density of charge carriers in the germanium is 2.0 × 1013 cm-3. Each charge carrier has a charge equal to the charge on an electron.
What is the average drift velocity of the charge carriers in the germanium?
A 0.18 m s-1 B 18 m s-1 C 180 m s-1 D 1800 m s-1
Solution:
Answer: A.
I = nqAv
Drift velocity v = I / nqA
We need to convert the quantities given into SI units.
Cross-sectional area A = 1.0 cm2 = 1.0×10-4 m2
Number density n = 2.0×1013 cm-3
That is, in 1 cm3, there are 2.0×1013 charge carriers
1 cm3 = 1×10-6 m3
1 cm3 - - > 2.0×1013 charge carriers
1×10-6 m3 - - > 2.0×1013 charge carriers
1 m3 - - > (2.0×1013) / (1×10-6) = 2.0×1019 charge carriers
So, number density n = 2.0×1013 cm-3 = 2.0×1019 m-3
Drift velocity v = I / nqA
Drift velocity v = (56×10-6) / (2.0×1019 × 1.6×10-19 × 1.0×10-4)
Drift velocity v = 0.175 m s-1 = 0.18 m s-1
Post a Comment for "A slice of germanium of cross-sectional area 1.0 cm2 carries a current of 56 μA. The numbe"