# phy 5 question on capacitorsWatch

This discussion is closed.
13 years ago
#41
(Original post by hajira)
talkin abt capacitors, i remember somewhere i was asked wats the reason for havin a resistor in a capacitor charging circuit
might b incredibly dumb, but i cant think of a plausible argument

suggestions?
You need a resistor if you don't have a power pack. Also ff you don't use a resistor the capacitor will charge v.quickly and it will be difficult to take measurements.
0
13 years ago
#42
Experiment
Method 1 (constant current method)
Circuit
For a given V record time to charge capacitor at a constant rate
For a range of values of V
Use Q = It to calculate Q
Plot Q V straight line graph through origin/ sketch graph/ divide Q/V and obtain constant value.

Method 2:
Circuit
For a given value V measure I and t
Plot I t find area under the graph Q
Repeat for a range of values of V
Plot Q V for a straight line graph through origin/ sketch graph/ divide Q/V and obtain constant value.

Method 3 (Joule metre method)
Circuit
Record V and energy stored
For a range of V
Determine Q from Â½ QV or (Q^2)/2C
Plot Q V straight line graph through origin/ sketch graph/ divide Q/V and obtain constant value.

[ Coulomb meter (will not work with this value of capacitor)
Circuit ; record charge Q on Coulomb meter ; for a range of values of V; Plot Q V straight line through origin â€“ Max 3]

this was the mark scheme for this question (jan 2005)
hope it helps
0
13 years ago
#43
(Original post by bassman)
Experiment

this was the mark scheme for this question (jan 2005)
hope it helps
0
13 years ago
#44
(Original post by nas7232)
You need a resistor if you don't have a power pack. Also ff you don't use a resistor the capacitor will charge v.quickly and it will be difficult to take measurements.
thanx
0
13 years ago
#45
yeah sry just realised the coulombmetre is only applicable is the charge is less than a microcoulomb. you want to plot current against time with a resistor in series in the dischargine circuit, but this way youll have to plot lots of graphs and lose accuracy in the area under the curve buisness...

Id prefer the energy method.
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