A capacitor of capacitance 
is connected to a battery of electromotive force (e.m.f.) 
in the circuit shown in the figure below.
The two-way switch S is initially at position X. P and Q are identical long straight wires, each with a resistance of 
. These wires are placed near to, and parallel to, each other. Wire Q is connected to a voltmeter. At time 
, switch S is moved to position Y so that the capacitor discharges through wire P. Calculate the time constant 
of the discharge circuit.
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