a potential difference of 2.5 V is applied across the faces of a germanium crystal plate. The face area of the crystal is 1 cm2 and it's thickness is 1.0 mm. The free electron conc. in germanium is 210 19 /m3 and the electron and holes mobilities are 0.33 m2/Vs and 0.17 m2/Vs respectively . The current across the plate will be.

The volume of germanium plate=Area×thickness=1×10-4×1×10-3=1×10-7mTherefore total number of free electrons in the plate=2×1019×10-7=2×1012Thus  charge on these electrons=ne=2×1012×1.6×10-19=2×10-7CThe resistivity ρ=1neμe+μh=13.2×10-70.33+0.17=1071.6=0.625×107ohm-metreThe resistance R=ρlA=0.625×107×10-310-4=0.625×108ohmSo the current through the germanium plate I=VR=2.50.625×108=4×10-7A

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