初中物理电路图题大全

Question

如题所述

Answer 1

当开关s1、s2都闭合时，r1、r2、l并联，灯正常发光得
u=ul
当开关s1、s2都断开时，r1、r2、l串联
u^2/r1=16w
ul’^2/rl：u^2/rl=1：4
(ul'/u)^2=4
ul'/u=2
ul'=0.5u
u1+u2=u-ul'=u-0.5u=0.5u
r1+r2=(u1+u2)/i=0.5u/i
rl=ul'/i=0.5u/i
所以
rl=r1+r2
r串=r1+r2+rl=2rl
u^2/r1=16w
①式
(u/r串)^2r1=1w
u^2r1/4rl^2=1w
②式
①式/②式得
4rl^2/r1^2=16
(rl/r1)^2=4
rl/r1=2
rl=2r1
r2=rl-r1=2r1-r1=r1
即
r1=r2
u^2/r1=16w
u^2/(0.5rl)=16w
pl=i^2rl=i^2×2r2=2i^2r2=2×1w=
2w
p额=4pl=
8w
选ad