Direct-current circuit/Kirchhoff's law problem

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SUMMARY

The discussion focuses on solving a direct-current circuit problem using Kirchhoff's laws. The circuit parameters include an electromotive force (emf) of ε1 = 27.0 V, resistances R1 = 6.00 Ω and R2 = 3.00 Ω. The correct answers for the questions posed are: the current in resistor R is 2 A, the resistance R is 4.5 Ω, and the unknown emf ε is 42 V. When the circuit is broken at point x, the current in resistor R changes, necessitating a reevaluation of the circuit to determine the new current distribution.

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Homework Statement


"In the circuit shown in the figure below, ε1 = 27.0 V, R1 = 6.00 Ω, and R2 = 3.00 Ω."
https://www.webassign.net/yf/27-29alt.gif

(a) Find the current in resistor R.
(b) Find the resistance R.
(c) Find the unknown emf ε.
(d) If the circuit is broken at point x, what is the current in resistor R?

I need help with understanding part d, please!

Homework Equations


I = V/R

The Attempt at a Solution


I1 + I2 - I3 = 0

ε - I2R2 - I1R2 = 0
ε1 - ε + I1R1 - I3R3 = 0

(a) Find the current in resistor R.
2 A
(b) Find the resistance R.
4.5 Ω
(c) Find the unknown emf ε.
42 V
(d) If the circuit is broken at point x, what is the current in resistor R?
2 A (wrong)

What am I doing wrong? Wouldn't the current in resistor R then be 9 V/4.5 Ω = 2 A?
 
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When you break the circuit at x it removes that branch from the circuit. It will no longer conduct current. This will change the distribution of currents and voltages in the remainder of the circuit.

Assume that component values don't change, so the value of R that you found previously remains the same. Draw the "new" circuit accordingly and determine the current.
 

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