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Comparing the effectiveness of ionizing and photoelectric smoke detectors Featured science projectScience project video


The materials required for this science fair project:

-    A photoelectric smoke detector
-    A ionizing smoke detector
-    2 alarms
-    A pack of cigarettes
-    A lighter
-    An ashtray
-    A long ruler
-    A stopwatch


1.    For this science fair project, the independent variable is the type of smoke detector used (photoelectric or ionizing) and the distance of the smoke detector from the source of the smoke. The dependent variable is the time taken for the smoke detector to trigger the alarm. This is determined by checking the time using a stopwatch. The constants (control variables) are the source of the smoke, the sensitivity of the smoke detectors and the temperature of the environment, which will remain at room temperature.

2.    Purchase a photoelectric smoke detector, an ionizing smoke detector and 2 alarms. Connect the alarm to the smoke detectors and test them before starting the experiment.

3.    Light a cigarette and place it on the ashtray. Hold the photoelectric smoke detector 200mm above the cigarette. Start the stopwatch and observe the time taken for the alarm to be triggered. Record the time taken to trigger the alarm in a table, as shown below.

4.    Repeat step 3, holding the ionizing smoke detector at a height of 200mm, and record the time taken for the alarm to trigger in a table, as shown below.

5.    Repeat steps 3 and 4 by holding the smoke detectors at 400mm, 600mm, 800mm and 1000mm above the cigarette. Record the time measured in a table, as shown below.

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Complexity level:
Project cost ($):
Time required:
1 hour for preparation, 2 hours for observation
Material availability:
Easily found at a hobby store
Safety concerns:

Adult supervision required. Take all necessary precautions to ensure fire safety. Be extremely careful when handling fire.