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Unformatted text preview: R2 (a)
1 kΩ
5 kΩ 2 mA +
vo
− 4 kΩ Figure 2.122
Voltmeter 2.63 (b) Figure 2.120
2.61 For Prob. 2.60. (a) Find the current i in the circuit of Fig. 2.121(a).
(b) An ammeter with an internal resistance of 1 is
inserted in the network to measure i as shown in
Fig. 2.121(b). What is i ?
(c) Calculate the percent error introduced by the
meter as An ammeter model consists of an ideal ammeter in
series with a 20 resistor. It is connected with a
current source and an unknown resistor Rx as shown
in Fig. 2.123. The ammeter reading is noted. When
a potentiometer R is added and adjusted until the
ammeter reading drops to one half its previous
reading, then R = 65 . What is the value of Rx ? Ammeter
model I
Rx 60 Ω Figure 2.123
2.64 v v (a)   R 16 Ω 40 Ω V For Prob. 2.62. A 4V +
− 100 kΩ 20 Ω i−i
× 100%
i
i 60 Ω (b) (d) Find the percent error if the internal resistance
were 36 k . 5 kΩ Ammeter 4V +
− v o − vo
× 100%
vo 2 mA 71 eText Main Menu  Textbook Table of Contents  For Prob. 2.63. The circuit in Fig. 2.124 is to control the speed of a
motor such that the motor draws currents 5 A, 3 A, Problem Solving Workbook Contents 72 PART 1 DC Circuits and 1 A when the switch is at high, medium, and
low positions, respectively. The motor can be
modeled as a load resistance of 20 m . Determine
the series dropping resistances R1 , R2 , and R3 . 2.65 An ohmmeter is constructed with a 2V battery and
0.1mA (fullscale) meter with 100 internal
resistance.
(a) Calculate the resistance of the (variable) resistor
required to be in series with the meter and the
battery.
(b) Determine the unknown resistance across the
terminals of the ohmmeter that will cause the
meter to deﬂect half scale. 2.69 An electric pencil sharpener rated 240 mW, 6 V is
connected to a 9V battery as shown in Fig. 2.126.
Calculate the value of the seriesdropping resistor
Rx needed to power the sharpener. Low
R1 10A, 0.01Ω fuse
Medium
High R2 6V R3
Motor Figure 2.124 For Prob. 2.64...
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This note was uploaded on 07/16/2012 for the course KA KA 2000 taught by Professor Bkav during the Spring '12 term at Cambridge.
 Spring '12
 bkav

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