phy17-2

phy17-2 - For HW you will see a lot of problems with 2 out...

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For HW : you will see a lot of problems with 2 out of I, R, V given all three are known with V=IR A voltage of 120 V is applied to a 100 light bulb. What is the number of electrons going through the light bulb in 5 seconds?

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Different materials have different values of Conductors Aluminum: 2.82 x 10 -8 ( m) Copper: 1.72 x 10 -8 ( m) Indium: 8 x 10 -8 ( m) Gold: 2.44 x 10 -8 ( m) Tungsten: 5.6 x 10 -8 ( m) Semiconductors: Silicon: 20 - 2300 ( m) Insulators: Wood: 3 x 10 10 ( m) 17.5 Temperature Variation of Resistivity
= 0 [1 + (T - T 0 )] : temperature coefficient of resistivity at T and 0 at T 0 If two temperatures are given, take the lower one as T 0 17.5 Temperature Variation of Resistivity Material Resistivity (Ω-m) at 20°C Coefficient Silver 1.59×10 -8 .0038 Copper 1.72×10 -8 .0039 Aluminium 2.82×10 -8 .0039 Tungsten 5.60×10 -8 .0045 Iron 1.0×10 -7 .005 Tin 1.09×10 -7 .0045 Platinum 1.1×10 -7 .00392 Lead 2.2×10 -7 .0039 Manganin 4.82×10 -7 .000002 Constantan 4.9×10 -7 .00001 Mercury 9.8×10 -7 .0009 Nichrome 1.10×10 -6 .0004 Carbon 3.5×10 -5 -.0005 Germanium 4.6×10 -1 -.048 Silicon 6.40×10 2 -.075 In semiconductors and insulators: Resistivity decreases with increasing temperature. Electrons are not able to move freely at T=0 K. The higher the temperature, the more electrons are freed and move. For most metals,

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phy17-2 - For HW you will see a lot of problems with 2 out...

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