PHY301-GDB-opened from 4th February 2016 at 12:00am

[Abdur BSCS]

The topic is:

 “You have two materials, one is Metal and other is semiconductor. How the decrease in temperature affects the Metal conductivity and increase of temperature effects the conductivity of semiconductor.  Tell the scientific reason behind this effect of conductivity”

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[Abdur BSCS]

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[Abdur BSCS]

The band gap in the metal is small and thus the electrons can easily take a leap to conduction band and conduct electricity but with increase in temperature, the thermal motion makes the electrons to collide and disturb the free flow. Thus, conductivity is decreased. However, with decrease in temperature, the thermal effect is nullified and the electrons can flow smoothly without hindrance and thus conductivity increases.
In semi conductors, the band gap is big but small enough for few electrons to take a leap to the conduction band and conduct electricity to some extent. However with increase in temperature they get charged with thermal energy which is sufficient to overcome the energy barrier and leap to the conduction band and thus, their conductivity increases.

[Abdur BSCS]

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[Abdur BSCS]

conductivity of a material depends directly both on the number n of free electrons per unit volume and on the average time τ between collisions. As we increase temperature, average speed of the electrons, which act as the carriers of current, increases resulting in more frequent collisions. The average time of collisions τ, thus decreases with temperature which decreases conductivity of metals. In semiconductors the number of free electrons increases with increasing tempreture,thus increasing conductivity.

[+ M.Tariq Malik]

PHY301 - Circuit Theory GDB No. 1 Solution Fall 2015 Due Date Feb 04, 2016

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[Abdur BSCS]

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