Need help with 1 and 2 12 points MI4 102.045 (a) In gold at room temperature, th

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Need help with 1 and 2 12 points MI4 102.045 (a) In gold at room temperature, the mobility of mobile electrons is about 4.3 x 103 (m/s)V/m), and there are about 5.9 x 1028 mobile the mobility u from this measurement. electrons per m, calculate the conductivity . In actual practice, it is usually easier to measure the conductivity and deduce (b) what are the correct units for ? (A*m)/V 0 (A/m2/(V/m (Arm)/(V/m2) O (m/A)/(V/m3) Additional Materials Section 19.2 2 O -12 points MI4 10.2.040 My Notes A carbon resistor is 7 mm long and has a constant cross section of 0.5 mm2. The conductivity of carbon at room tempe × 104 per ohm-m. In a circuit its 15 volts. Calculate the resistance R and the current I rature is -3 potential at one end of the resistor is 12 volts relative to ground, and at the other end the potential is amperes Additional Materials DSection 192

Explanation / Answer

Conductivity of gold is given by:

sigma = q*n*u

q = charge on electron = 1.6*10^-19

u = mobility of electrons = 0.0043 (m/s)/(V/m)

n = density of electrons = 5.9*10^28 electrons/m^3

Now using these values:

sigma = (1.6*10^-19 C)*(5.9*10^28 m^-3)*(0.0043 (m/s)/(V/m))

sigma = 4.06*10^7 (A/m)/V

Correct unit = (A/m)/V = (A/m^2)/(V/m) (OPTION B)

2.

Resistance is given by:

R = L/(sigma*A)

Using given values:

R = 7*10^-3/(3*10^4*0.5*10^-6)

R = 0.467 ohm

Now using ohm's law:

V = i*R

V = Voltage drop between resistor = 15 - 12 = 3 V

i = V/R = 3/0.467

i = 6.42 Amperes

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