Aim: To find the half-life of a liquid draining from a burette

1. Ronaldo Degazon Wednesday 13/02/13 Physics Lab #21 Radio-activity 2
Title: Radioactivity 2
Aim: To find the half-life of a liquid draining from a burette
Apparatus: Burette, water, stopwatch, beaker, retort stand
Procedure:
1. The apparatus was set up as shown in the diagram above, with the burette
filled with water slightly above the 50cm mark.
2. The tap was adjusted so that it drained moderately.
3. With the tap open, the stopwatch was started when the water level reached
50cm3.
4. The time – t – was recorded on the stopwatch for every 5cm3 decrease in
volume, using the split time option on the stopwatch.
5. Steps 1-4 were repeated, taking the time as t2.
6. The average time – tA – for each level of water remaining was calculated.
7. The volume of water remaining – v – and the corresponding time – tA – was
used to plot a graph of volume remaining against time.
Results: Below – Table illustrating results recorded
Volume of Water Left /
cm3
Time/s
1 2 Average
50 0 0 0
45 43 44 44
40 92 91 91
35 148 139 143
30 207 190 199
25 275 248 262
20 338 310 324
15 408 374 391
10 487 444 465
5 574 519 546
0 665 611 638
Discussion:
Radioactive decay is the process by which by which an atomic nucleus of an unstable
atom loses energy by emitting ionizing particles.

2. The half-life of a radioactive element is the time it takes for half the original number of
radioactive nuclei to decay. The half life of the water draining from the tap was the average
time it took for the original water level to fall to half.
The volume of water released at a point in time depends on the volume of water in the
burette. The greater the amount of water in the burette (its depth), the more pressure the
water at the bottom will receive because depth is directly proportional to pressure. Hence the
more pressure that the water to the bottom receives, the greater the mass that will flow out
per unit time. The equation for fluid pressure is shown below:
𝑃 𝑎𝑡 + ℎ × 𝑔 × 𝜌
Where Pat = Atmospheric Pressure
h = depth
g = acceleration due to gravity
𝜌 = density of liquid
This systemof water draining from a tap is analogous to the decay process because the
less water there is, the longer it will take for water to leave the tap (decay). Radioactive decay is
a similar process; the more radioactive atoms there are the more radioactive decay that is likely
to occur.
Sources of Error:
1. Parallax error when reading the volume of liquid remaining off the burette.
2. Slow reaction time to press the stopwatch may have reduced accuracy of time
recordings.
3. Zero error; the rate of flow when the tap was just opened may have been slower than
the rate a few seconds after.
4. A faulty stopwatch may have affected the time readings.
5. The extent to which the tap was opened may have been different for the 1st and 2nd set
of readings.
Precautions:
1. The burette was read in such a way so as to reduce parallax error as much as possible.
2. Two sets of readings were taken and the average was found to increase the accuracy of
the results.

3. 3. The burette was filled with slightly more than 50cm3 so that the rate of flow at 50cm3
wasn’t slower than normal (to minimize zero error).
4. It was ensured that the stopwatch was functioning properly.
5. It was ensured that the opening of the tap remained the same for both sets of readings.
Conclusion: The half life of water draining from a tap opening was found to be