This study demonstrated that the constant average speed of a dynamic car could be measured and calculated using the smartphone magnetometer. The apparatus setup was built using a dynamic car, a linear track up to 1.50 m, a bunch of magnets, and a smartphone magnetometer application. The smartphone magnetometer application, ‘Physics Toolbox Suite’, was free for the experiment. The magnet and smartphone magnetometer were attached on a linear track and dynamic car, respectively. When the dynamic car are moving on the car track, the smartphone magnetometer will measure the magnetic field value versus the time relation. The magnetic field value will fluctuate, increasing when close to the magnet or decrease when the distance from the magnet increases. The magnetic field properties (peaks time) versus the magnet distance position were analyzed using linear fitting, and we find the average speed of the dynamic car. We hope that this magnetometer experiment will be valuably used in general physics laboratories.

In this paper, we report on a homemade optical spectrometer using diffraction grating and image processing techniques. This device was designed to produce spectral images that could then be processed by measuring signal strength (pixel intensity) to obtain the light source, transmittance, and absorbance spectra of the liquid sample. The homemade optical spectrometer consisted of: (i) a white LED as a light source, (ii) a cuvette or sample holder, (iii) a slit, (iv) a diffraction grating, and (v) a CMOS camera (webcam). In this study, various concentrations of a carbon nanoparticle (CNP) colloid were used in the particle size sample test. Additionally, a commercial optical spectrometer and tunneling electron microscope (TEM) were used to characterize the optical properties and morphology of the CNPs, respectively. The data obtained using the homemade optical spectrometer, commercial optical spectrometer, and TEM showed similar results and trends. Lastly, the calculation and measurement of CNP size were performed using the effective mass approximation (EMA) and TEM. These data showed that the average nanoparticle sizes were approximately 2.4 nm and 2.5 ± 0.3 nm, respectively. This research provides new insights into the development of a portable, simple, and low-cost optical spectrometer that can be used in nanomaterial characterization for physics undergraduate instruction.

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