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# what tf am i doing wrong in this capacitor - circuit resistance qn???!! watch

1. the capacitors capacitance is 10 µF and the question is "Take readings from the graph to show that the resistance of the electronic circuit
is in the range 1000 Ω to 2000 Ω. "

i converted time from ms to seconds and i tried it with so many values (like 3.5 for V0, and 4.5 for V and 5 ms for the time( but im not getting the answer??? can someone please work it out??? thanks
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2. I used Vo = 5.0V at 3ms and V1=3.5 at 10ms

In otherwords, drops from 5.0 to 3.5 in 7ms and it gave me 1963 Ohms

I'm using V = V0 exp (t/RC)
3. (Original post by phys981)
I used Vo = 5.0V at 3ms and V1=3.5 at 10ms

In otherwords, drops from 5.0 to 3.5 in 7ms and it gave me 1963 Ohms

I'm using V = V0 exp (t/RC)

i did that and got that answer too but the ms says

"R approx 1700 Ω (allow 1600 – 1800)" so 1963 is outside that range....
4. That's purely down to reading the graph.

If you notice, the MS also says Corresponding time interval for a change in V eg 6-7 ms for ∆V = 2V

The method is exactly the same.

If I use 6ms instead of 7 for the same voltage drop, I get 1682 Ohms

If you use the right method and your answer is outside the range, you lose the final mark but get the rest.
5. (Original post by phys981)
That's purely down to reading the graph.

If you notice, the MS also says Corresponding time interval for a change in V eg 6-7 ms for ∆V = 2V

The method is exactly the same.

If I use 6ms instead of 7 for the same voltage drop, I get 1682 Ohms

If you use the right method and your answer is outside the range, you lose the final mark but get the rest.

thank youu could u pls explain the next part to me as well the question us
"Figure shows that the voltage supplied to the electronic circuit still varies.
How could the student make it more constant?" and the answer is use larger capacitor

how does using larger capacitor make it more constant
6. (Original post by lolatmylifeee)
thank youu could u pls explain the next part to me as well the question us
"Figure shows that the voltage supplied to the electronic circuit still varies.
How could the student make it more constant?" and the answer is use larger capacitor

how does using larger capacitor make it more constant
The problem is that the PD decays over time after each peak

for low values of RC (short time constant) it will decay more rapidly than for high values of RC

so you want to increase RC... and the R is fixed

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