An Inexpensive Timer In connection with the laboratory work in physics, chemistry, and physical sciences, many times it is desired to have a timer, which will give a signal to the class, a t a predetermined constant interval of time, to record an event. This is ~articulerlyso in introductory courses, where the emphasis is on qualitative measurement to understand the besic concepts. -such a timer is useful, for example, when the students want to record the temperature every 60 seo or 30 see, to plot a cooling curve. Such a timer is not available a t a reasonable price. We have made a convenient timer by recording on tape the sound of an electric buzzer, operated manually a t an interval of one minute and with the tape speed of 1'h in./sec. When the tape is played back, i t can be used as a timer, giving the sound signal at a n interval of 60 sec, 30 sec, or 15 seo when played a t the speeds of l'/s, 33/r, or 7I/n in./see, respectively.
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Journal of Chemical Education
