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799_Physics ProblemsTechnical Physics

# 799_Physics ProblemsTechnical Physics - Chapter 28 139(e...

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Chapter 28 139 (e) Increasing resistor 3 increases the equivalent resistance of the entire circuit. The current in the circuit, which is the current through resistor 1, decreases. This decreases the potential difference across resistor 1, increasing the potential difference across the parallel combination. With a larger potential difference the current through resistor 4 is increased. With more current through 4, and less in the circuit to start with, the current through resistors 2 and 3 must decrease. To summarize, II I I 41 2 3 increases and and decrease ,, . (f) If resistor 3 has an infinite resistance it blocks any current from passing through that branch, and the circuit effectively is just resistor 1 and resistor 4 in series with the battery. The circuit now has an equivalent resistance of 4 R . The current in the circuit drops to 3 4 of the original current because the resistance has increased by 4 3 . All this current passes through resistors 1 and 4, and none passes through 2 or 3. Therefore I I I I 12 3 4 3 4 0 3 4 == = = . Section 28.3 Kirchhoff’s Rules P28.20 +− = 15 0 7 00 2 00 5 00 0 1 .. afaf af I 500 700 1 = I
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