The bit rate of a sound recorder affects the file size by: when the bit rate is higher the sound quality's better but if the bit rate is lower the sound quality is lower as well meaning that the higher quality the higher the file size.
here there is a image of how bit rate works. sound waves or vibrations as i like to call them are how we hear noise. originally these would be curved lines but to make it view able we put lines in it. meaning the more lines the higher the bit rate.