Demonstrations of magnetic phenomena: measuring the air permeability using tablets

Abstract

We use a tablet to determine experimentally the dependencies of the magnetic field (B) on the electrical current and on the axial distance from a coil (z). Our data shows a good precision on the inverse cubic dependence of the magnetic field on the axial distance, B ∝ z −3 . We obtain with good accuracy the value of air permeability µair. We also observe the same dependence of B on z when considering a magnet instead of a coil. Although our estimates are obtained through simple data fits, we also perform a more sophisticated error analysis, confirming the result for µair. PACS numbers:The use of tablets and smartphone in science education expands possibilities for approaches that motivate students to understand better several physical phenomena [1][2][3][4]. In particular, tablets were shown as good tools to measure magnetostatic responses in current-carrying wires. This interesting work is about magnetic field sensoring [1]. It reports a simple way of obtaining experimentally the linear dependence between the magnetic field B and the number of turns N in the current-carrying coil using an "app" for iPad [5]. However, additional dependences of B are still not discussed, some of which we show in this paper leading to a wider description of this kind of system.We determine the dependencies of B on the electric current I and on the axial distance z in a coil, in suitably conditions using an iPad and the same free app MagnetMeter [5] (we suggest a similar app for Android [6]). We also perform the similar experiments with a small magnet instead of a coil. For the coil, we also make a good estimate for the magnetic permeability of the air µ air ∼ = µ 0 ≡ 4π × 10 −6 Hm −1 . The demonstration set used is composed by an electrical circuit, a ruler and a book. The circuit is formed by the following components, all of them connected in series: a wirewound potentiometer with resistance up to 30Ω; a resistor with 10Ω; an electrical source from a cell phone (max. output current ∼ 0.9A); a digital multimeter and a coil (internal diameter 2R i = 1.91 cm and external diameter 2R e = 2.42 cm and N = 62 turns).

Magnetic field ‘flyby’ measurement using a smartphone’s magnetometer and accelerometer simultaneously

“…Until now a few smartphone-based experiments focusing on electromagnetism have been proposed in the literature (see for example [7][8][9]). In general, in these experiments the value of the magnetic field is obtained point by point and the distance is measured using a ruler like in traditional approaches.…”

Measurement of the characteristics of the Earth’s magnetic field using a smartphone magnetic sensor

“…In the literature, the smartphone-based acceleration sensor has been employed in a rather quick measurement of the acceleration due to gravity [8] and in analyzing simple pendulum phenomena [9]. In contrast, applications of the magnetic field sensor of the smartphone device are less discussed [10], but recently demonstrated for the measurement of the air permeability [11], the field distribution around small magnets [12], flyby measurements with combined acceleration and magnetic field recording [13], the average angular velocity [14], a magnetic pendulum to measure the acceleration due to gravity [15], and measurement of a spring constant [16].…”

Using smartphone pressure sensors to measure vertical velocities of elevators, stairways, and drones

“…Because of the availability of several sensors in these modern devices (accelerometers, gyroscopes, magnetometer, etc), several experiments can be implemented in laboratories (see past volumes from this journal or the column iPhysicsLab in Physics Teacher). The proposed experiments span a wide range of topics including mechanics [1][2][3][4][5][6][7], oscillations [8], waves [9,10], electricity [11], magnetism [12,13], and modern physics [14]. The most important advantages of using smartphones are both increasing availability among young people and the decreasing cost (in comparison with other sensors which are specifically designed for teaching purposes).…”