图甲电路闭合开关,电流表$A_{1}$的示数为$0.5A$,电流表$A_{2}$的示数为$0.3A$,则灯$L_{1}$、$L_{2}$的电阻之比为______.图乙电路闭合开关,$V_{1}$的示数为$2.5V$,$V$的示数为$6V$,则灯$L_{1}$、$L_{2}$的电阻之比为______；若灯$L_{2}$突然烧断了灯丝而熄灭,则$V_{2}$的示数为______$V$.