Robert Cinca - Physics
had been steady for a while. I then measured the size of the maximum surge current
(using the software’s tracer function, which allowed me to look at each recorded
point in detail). Measuring the time taken to reach the maximum surge current was
also done using the tracer function; however, to measure the surge current time I
had to judge where the final steady current was by eye (see below for comment on
precision). By varying the resistance in the variable resistor, I was able to plot results
for many different final currents. I then repeated my experiment with the second
filament bulb I had.
Control Variables
During my experiment, I had to control some variables in order for my experiment not
to be affected. Firstly, I used the same filament bulb for each experiment. In order for
there to be a surge current, I waited two minutes (with the circuit turned off) between
each measurement in order to let the filament bulb cool down. Whilst doing the
experiments, apart from changing the filament bulb (from the 0.15A one to 0.30A
one), I kept the same apparatus throughout.
Comment on Range Used
I used a range of final currents varying from 0.06A to 0.32A. I used the following
range because: on the lower end of my results, the percentage uncertainties were
becoming too great and the current was taking too long to reach a steady level. On
the top end of my results, I was limited by my filament bulbs, which could only take a
maximum potential difference of about 8 volts. Even so, my range was sufficiently
large enough for me to take lots of readings and be able to plot a reliable graph.
Limitations of the experiment
On the whole, the experiment was very precise, helped by the use of data studio
(which let me take readings every millisecond). The uncertainty in the final current is:
±0.01A. To improve this, I would use a more precise ammeter. The uncertainty of the
surge current time was determined by the half range of the experimental results,
which varied between ±0.004s and ±0.03s. Though precise, this could be improved
further by measuring the changing gradient of the surge current with time. The start
of the surge current is determined when the changing gradient of the surge current
with time is zero.
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