The following questions refer to the circuit shown in the figure, consisting of

Question

The following questions refer to the circuit shown in the figure, consisting of two flashlight batteries and two Nichrome wires of different lengths and different thicknesses as shown (corresponding roughly to your own thick and thin Nichrome wires). The thin wire is 59 cm long, and its diameter is 0.25 mm. The thick wire is 15 cm long, and its diameter is 0.39 mm.

(a) The emf of each flashlight battery is 1.5 volts. Determine the steady-state electric field inside each Nichrome wire. Remember that in the steady state you must satisfy both the current node rule and energy conservation. These two principles give you two equations for the two unknown fields.
E inside thin wire =   V/m
E inside thick wire = V/m

(b) The electron mobility in room-temperature Nichrome is about 7 10-5 (m/s)/(N/C). How long (in minutes) does it take an electron to drift through the two Nichrome wires from location B to location A?
= min

(c) On the other hand, about how long did it take to establish the steady state when the circuit was first assembled? Give an approximate, not precise numerical answer.
= s

(d) There are about 9 1028 mobile electrons per cubic meter in Nichrome. How many electrons cross the junction between the two wires every second?
= electrons/s

Explanation / Answer

From the given question,

thin wire = 59 cm long,

thin wire diameter = 0.25 mm.

The thick wire = 15 cm long,

thick wire diameter = 0.39 mm.

(a) The emf of each flashlight battery is 1.5 volts.

Electric field= voltage/length

Ethin wire=1.5/0.59=2.54 N/C

Ethick wire=1.5/0.15=10 N/C

(b) The figure is not given,

time taken = distance travelled/ mobility

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