DC circuits problem: I am having trouble solving for part (b). Step by step expl

Question

DC circuits problem:

I am having trouble solving for part (b).

Step by step explanation would be helpful.

6. A gasoline gauge for an automobile is shown schematically in Fig. 31-26. The indicator (on the dashboard) has a resistance of 10 . The tank unit is simply a float connected to a resistor that has a resistance of 140 when the tank is empty, 20 when it is full, and varies linearly with the volume of gaso- line. Find the current in the circuit when the tank is (a) empty (b) half full, and (c) full. Rindicator 12 V Connected through chassis Rank FIGURE 31-26. Exercise 6.

Explanation / Answer

Given,

Ri = 10 Ohm ; V = 12 V

a)When empty Rtank = 140

Req = Ri + Rtank

Req = 10 + 140 = 150 Ohm

I = V/R = 12/140 = 0.086 A

Hence, I = 0.086 A

b)when half

Rt = (140 - 20)/2 = 60 Ohm

Req = 10 + 60 = 70 Ohm

I = 12/70 =0.171 A

Hence, I = 0.171 A

c)when full

Req = 10 + 20 = 30 Ohm

I = 12/30 = 0.4 A

Hence, I = 0.4 A

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