Ultrasound is a longitudinal mechanical wave whose frequency is above 20 000 Hz. Although they are outside the range of human hearing, ultrasonic waves are widely used in various fields of human activities such as medicine, industry, technology, and education. This thesis will present one example of the use of ultrasound in physics teaching for gifted students. An experiment in which the unknown concentration of sugar dissolved in distilled water is determined using ultrasonic waves will be described and analyzed. To understand this experiment, it is necessary to know the Debye-Sears effect, which describes the diffraction of light on an optical grating created by the action of ultrasound in distilled water (solution). It can be concluded that increasing the concentration of sugar increases the speed of sound in the solution, while the distance between the diffraction maxima of the same order decreases. Using the calibration curve, which represents the dependence of the mass fraction of sugar on the distance between the maxima of the same order and the measured distance, the unknown sugar concentration is determined. At the end of the paper there is a curriculum so that the mentioned experiment can be realized as a research project that enables gifted students to strengthen existing and develop new skills and interests.