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Two of the three resistors in FIGURE EX28.22 are unknown but equal. The total resistance between pointsaandbis75Ωis . What is the value of R?

Short Answer

Expert verified

The value of Ris 240Ω

Step by step solution

01

Given Information  

We have to find the value ofR.

02

Simplify 

If two points and there are resistors connected at both ends of the points then it is called the resistors are connected in parallel. This is obvious when the resistors are aligned side by side. The potential difference across the resistors is the same in parallel connection. The equation shows the equivalent resistance for the parallel connection in the form

1Req=1R1+1R2+....+1RN(1)

We have three resistors in parallel where R1=200Ωand other two resistors are Rand . We are given the equivalent circuit by Req=75Ω. By equation (1)

1Req=1R1+1R2+....+1RN1R=1Req-1R1(2)R=11Req-1R1-1

Putting the value for ReqandR1into equationlocalid="1648916142131" (2)to get Rby

R=21Req-1R1-1=2175Ω-12000Ω-1=240Ω

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Most popular questions from this chapter

A battery is a voltage source, always providing the same potential difference regardless of the current. It is possible to make a current source that always provides the same current regardless of the potential difference. The circuit in FIGURE P28.56 is called a current divider. It sends a fraction of the source current to the load. Find an expression for Iloadin terms of R1,R2and Isource.You can assume that the load’s resistance is much less thanR2.

A 12 V car battery dies not so much because its voltage drops but because chemical reactions increase its internal resistance. A good battery connected with jumper cables can both start the engine and recharge the dead battery. Consider the automotive circuit of FIGURE P28.65.

a. How much current could the good battery alone drive through the starter motor?

b. How much current is the dead battery alone able to drive through the starter motor?

c. With the jumper cables attached, how much current passes through the starter motor?

d. With the jumper cables attached, how much current passes through the dead battery, and in which direction?

The capacitor in FIGURE P28.73begins to charge after the switch closes atτ=0s..

a. What is Vc a very long time after the switch has closed?

b. What isQmaxin terms of E,R, and C?

c. In this circuit, does localid="1649091794998" I=+dQ/dtor-dQ/dt? Explain.

d. Find an expression for the current I at time t. Graph I from τ=0to localid="1649091939933" t=5r.

In FIGURE EX28.31, what is the value of the potential at points aandb?

A circuit you’re using discharges a 20μFcapacitor through an unknown resistor. After charging the capacitor, you close a switch at t=0sand then monitor the resistor current with an ammeter. Your data are as follows:

Use an appropriate graph of the data to determine

(a) the resis-tance and

(b) the initial capacitor voltage.

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