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This is the circuit: enter image description here

At t=0s, switch is moved to position 1 and the time constant= 1ms

At t=10ms, switch is moved to position 2, it is assumed there is no leakage current

At t=20ms, switch is moved to position 3 and the time constant is 1.5ms

The waveforms of position 1 and 3:

enter image description here

So I understand what's going on before 10ms but what's confusing me is after it, so if the time constant after 10ms(position 3) is 1.5ms then after five time constant where the capacitor is supposed to be fully discharged then must be at 1.5x5 = 17.5ms but on the waveform it looks like it's saying after five time constant, the capacitor is fully discharged at 22.5ms, so what's going on ?

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    \$\begingroup\$ I think there's some confusion with the timing of the switch. it looks to me as though it switches from 1-2 sometime between 5ms and 10ms, and then from 2-3 at 10ms. \$\endgroup\$ – brhans Jan 10 '18 at 23:05
  • \$\begingroup\$ But why the capacitor is discharged at 22.5ms ? five time constant after 10ms must be 17.5ms \$\endgroup\$ – BigRedMachine Jan 10 '18 at 23:09
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The 22.5ms label is wrong, but the rest of the graph is right. There's equal horizontal spacing between 0ms, 5ms, 10ms, and 15ms, with about half as much space between 15ms and the final +5τ' tick. This suggests that the +5τ' tick is actually at 17.5ms, which is the correct answer.

Textbooks sometimes have errata on the publisher's web site. You can check there to see if they've already noticed this error. If not, they should have a way for you to report it.

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  • \$\begingroup\$ Ok thanks, for the past two hours I had been trying to convince myself 22.5ms is correct. \$\endgroup\$ – BigRedMachine Jan 10 '18 at 23:21

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