2015 Evaluative

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  • Created by: 3sho1416
  • Created on: 02-02-15 14:08
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Capacitor discharge
1 Read information given and setup
circuit as shown.
2 Time value (e.g. 10s) and resistor value
given
3 Draw table for figures found from
Voltmeter (three readings for accuracy +
find an average) n> number of capacitors
(when adding more capacitors add in
series), do 5/6 at least
V> Voltage in Voltmeters(/V)
n V 1/V V 2/V V 3 /V V Avg/V lnV0
1 e.g.2.20 2.20 2.19 2.20 0.788
2
3
4 Draw graph in(V/V) (yaxis) against n(xaxis). + Line of best fit. (graph
should look like this:
5 Determine yintercept of graph drawn = mine 0.860 V
6 Gradient of graph (draw triangle within first and last point = dy/dx) do this twice
then find average, my gradient = 0.0789
hn
V = V
0e
7 Where V 0 is the initial p.d. across the arrangement of capacitors and h is a
constant. Use your values of gradient and yintercept to determine a value
for h and to confirm your value V 0.
(Here rearrange above equation to show equation of line drawn by you from
the experiment that you carried out)
Write out in this layout
hn
V = V0e
lnV=lnV 0 hn
lnV= hn+ lnV 0
Gradient =h Xaxis=n lnV0 =yintercept
Hence initial voltage V0= e(value of yintercept)
0.860
Mine V0= e
V0 = 2.36V (it's never higher than e.m.f value of cell)
8 k= gradient , so determine Capacitance
K=t/CR
C= answer in Farads

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Capacitor discharge
9 Draw worst acceptable line, use this to determine the percentage
uncertainty in the graph.
yx-yx
yx ×100
10Determine uncertainty of C
Work out uncertainty of t, R, k, add them to work put % uncertainty of C.
11Comment on the reliability using table + graph
Scattered values on graph hence inaccurate
Readings of voltmeter are only given to 3s.f.
12Determine % difference between the experimental value of C & manufacture
value
a.…read more

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