Low-Cost Timer to Measure the Terminal Velocity of a Magnet Falling Through a Conducting Pipe

Abstract

D ropping a magnet into a conductive pipe (made up of copper or brass or aluminum) is a very popular demonstration in many physics classrooms and laboratories. In this paper we present an inexpensive timer that can be used to measure the terminal velocity of the magnet falling through a conducting pipe. The timer assembly consists of Hall effect switches connected to a digital stopwatch. The timer assembly was then used to observe the variation in the terminal velocity of the falling magnet with respect to the thickness of the copper pipes.

Discovery of misleading graph titles at many places of the traditional scientific literature

“…Examples of a few graphs, each with a good and proper title have been incorporated as ready reference. Existence of graph titles at many other places of the longrunning literature [7], [8], [13], [14], [16], [18], [20], [25], violating the traditional convention in the said context has been detected and one self-explanatory graph title for each of them has also been proposed. From the view point of clarity of understanding and ensuring quality graphing, getting rid of those misleading graph titles which are not in accordance with the traditional convention of graph drawing is essential and needs immediate attention.…”

“…Although many standard literature [5], [6], [9], [15], [22], [23], [24] follow the rule in respect of assigning a "Title" to a graph or in writing down the "Caption of Figure related to the graph" as has been mentioned earlier, violation of the above rule in respect of assigning the "Title" to a graph or in writing down the "Caption of the Figure related to a graph" has been observed at many other places of the traditional literature [8], [13], [14], [16], [18], [20], [25]. Let us consider first the graph shown in Fig.…”

“…In Fig. 8(b) of [18], Fall time (s) is plotted along X-axis and Magnet vertical distance (cm) is plotted along Y-axis, the caption of Fig. 8(b) being "Graph of fall time against Vertical distance of the falling magnet."…”

Measurement of the thermal coefficient of electrical resistivity of a nonmagnetic metal

“…Thus, the speed of the falling magnet through the tube depends on the electrical resistance of the tube. The electrical resistance of the tube depends on thickness of the tube's walls, [1] correlative diameter of the tube and of the magnet, on the resistivity of the tube material, and also on the temperature. The temperature dependence can be demonstrated by cooling the tube with liquid nitrogen or dry ice.…”

“…It turns out that the velocity of the magnet is lower when the temperature is lower. The speed of the falling magnet is constant except for brief transients when the magnet passes the top end of the tube and when it passes the bottom end of the tube [1]. Let us select a section of the tube where the magnet falls with a constant speed.…”