The de Broglie wavelength for an electron accelerated through the potential difference of \( V_1 \) volt is \( \lambda_1 \). When the potential difference is changed to \( V_2 \) volt, the associated de Broglie wavelength is increased by \( 50\% \). If \( (V_1/V_2) = (9/\alpha) \), then the value of \( \alpha \) is ________.
