An ammeter is used as shown in Figure P2.78. The ammeter model consists of an ideal ammeter in series with a resistance. The ammeter model is placed in the branch as shown in the figure. Find the current through R5 both with and without the ammeter in the circuit for the following values, assuming that RS = 20 ? , R1 = 800 ? , R2 = 600 ? , R3 = 1.2 k? , R4 = 150? , and vS = 24 V.
a. R5 = 1 k?
b. R5 = 100?
c. R5 = 10?
d. R5 = 1?
Known quantities:
Schematic of the circuit shown in Figure P2.78, value of the components.
Find:
The current through both with and without the ammeter, for the following values of the resistor :
a)
b)
c)
d) .
Analysis:
First we should find an expression for the current through in terms of and the meter resistance, . By the voltage divider rule we have:
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