Three bulbs The figure is a top view of a circuit containing three identical lig

Question

Three bulbs
The figure is a top view of a circuit containing three identical light bulbs (the rest of the circuit including the batteries is not shown). The direction of the North pole is toward the right. The connecting wires are made of copper.

http://www.webassign.net/mi3/19-073-PROB3roundwithcompass.jpg

(b) In the steady state, 5 1018 electrons pass location P1 every second. How many electrons pass location P2every second?

=2.5e18

(d) There are 6.3 1028 mobile electrons per cubic meter in tungsten. The cross-sectional area of the tungsten filament in bulb B1 is 0.01 mm2 (1 mm2 = 1 10-6 m2). The electron mobility in hot tungsten is 1.2 10-4(m/s)/(N/C). Calculate the magnitude of the electric field inside the tungsten filament in bulb B1.

I got the answer to B) but I need help with D)

Explanation / Answer

Given,

Three identicals bulbs are connected in a circuit.

(b)N(P1) = 5 x 1018

The number of electrons passing through P2 will be half of that passing through P1.

N(p2) = 5 x 1018 / 2 = = 2.5 x 1018

Hence, N(P2) = = 2.5 x 1018

This is because, the bulbs are identical ans has got the same resistance.

(d) N = = 6.3 x 1028

A1 = 0.01 mm2 = 1 x 10-8 m2

u = 1.2 x 10-4 m/s /N/C

We need to find the electric field inside the tungsten filament. Let it be E.

We know that,

i = N A u E

E = i / N A u = = 5 x 1018 / (6.3 x 1028) x (1 x 10-8 )x (1.2 x 10-4 ) = 66.14 N/C

Hence, E = 66.14 N/C.

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