In this case, it is seen that due to the effect of the temperature increase, the temperature is considered as a variable since it is modifying the piston's states. In addition, as long as the piston moved upward owing to the aforesaid temperature increase, the volume is considered as the other variable by cause of its change (when the piston moves upwards the volume increase). In such a way, there are two variables, temperature and volume. Neither pressure nor number of molecules are variable since the piston is a closed system and the piston's movement allows the pressure to keep constant.
Like any wave, a sound wave doesn't just stop when it reaches the end of the medium or when it encounters an obstacle in its path. Rather, a sound wave will undergo certain behaviors when it encounters the end of the medium or an obstacle. Possible behaviors include reflection off the obstacle, diffraction around the obstacle, and transmission (accompanied by refraction) into the obstacle or new medium
when there is a radical in the denominator, we should rationalize (mutiply the denominator and numerator by the radical) to get rid of the radical in the denominator.
With electrical energy, it's helpful to think of an on/off switch. When the switch is off, the electrical energy is stored as potential energy. When the switch is on, electrical energy is being used as kinetic energy.
