電學1問(10分)

禁似我份eep test1- -.....你又係讀EE?唔識sn信比我
用返你個答法[]<---錯的
a)
R(總)=R(左)+R(右)
=25//15+10//10//20
=75/8+4
=13.375(OHM)
I(總)=V/R(總)
=20/13.375
=1.495A
[[[the current through 25R = V/25=0.8A (#1)]]]
>>(1.495)x9.375/25=0.561A <---------- Current Divider(9.375=25//15)
[[[the current through 15R = V/15=1.33A (#1)]]]
>>(1.495)x9.375/15=0.935A <---------- Current Divider
[[[the current through 10R = V/10=2A (#1)]]]
>>(1.495)X4/10=0.598A <---------- Current Divider
[[[the current through 20R = V/20=1A (#1)]]]
>>(1.495)X4/20 =0.299A <---------- Current Divider

b)
[[[[the p.d across resistor 25R=I(總)x25=37.325V (#2)
the p.d across resistor 15R=I(總)x15=22.425V (#2)]]]]
the p.d across resistor 15R=the p.d across resistor 25R ( in paralle so V一樣)
1.495x9.375=14.02V
[[[[the p.d across resistor 10R=I(總)x15=14.95V (#2)
the p.d across resistor 20R=I(總)x15=29.9V (#2]]]]
the p.d across resistor 20R=the p.d across resistor 10R ( in paralle so V一樣)
1.495x4=5.98V
c)
P=IV
=0.299A X 5.98V
=1.79W

Last::
睇下 Current divider....好好用
#1記得有paralle唔可以用總V直接放入去計....如要放V入去......你當左邊R吸左14.02V 禁先計左邊果2個.....
#2 ..I 係paralle 果時會分流......電阻(R)大會少D電流所以唔可以又用總果個

25R係咪表示25 ohm呢
如果唔係的話答案就要用R表示了
下面的會用R來表示
如果R係ohm咁解
將d R代哂做1就ok了

為左容易d表達你知
我設左上25R為R1, 左下15R為R2
右上10R為R3, 右中10R為R4, 右下20R為R5
(a)
Let R_lhs and R_rhs be the total resistance of LHS and RHS respectively
1 / R_lhs = 1 / 15R + 1 / 25R
1 / R_lhs = 40 / 375R
　 R_lhs = 75R / 8
1 / R_rhs = 1 / 10R + 1 / 10R + 1 / 20R
1 / R_rhs = 5 / 20R
　 R_rhs = 4R
Total resistance of whole circuit = R_lhs + R_rhs = 107R / 8
By V = IR,
(2 0) = Ｉ(107R / 8)
　Ｉ = (160 / 107R) A　　　[OR (1.495/R) A]

For R1 and R2
　　　V1 = V2
　Ｉ1 R1 = Ｉ2 R2
Ｉ1 (25R) = Ｉ2 (15R)
Ｉ1 :Ｉ2 = 3 : 5

Ｉ1 = (160 / 107R) x 3/8 = (60 / 107R) A　　　 [OR (0.561/R) A]
Ｉ2 = (160 / 107R) x 5/8 = (100 / 107R) A　　　[OR (0.934/R) A]

For R3, R4 and R5
　　　V3 = 　 V4 　 = V5
　Ｉ3 R3 =　Ｉ4 R4　= Ｉ5 R5
Ｉ3 (10R) = Ｉ4 (10R) = Ｉ5 (20R)
Ｉ3 :Ｉ4 : Ｉ5 = 2 : 2 : 1

Ｉ3 = Ｉ4 = (160 / 107R) x 2/5 = (64 / 107R) A　　　[OR (0.598/R) A]
Ｉ5 = (160 / 107R) x 1/5 = (32 / 107R) A　　　　　　[OR (0.299/R) A]

(b)
For R1 and R2
　V1
= Ｉ1 R1
= (60 / 107R) (25R)
= 1500/107 V　　　　　　　[OR 14.0 V]
V1 = V2 = 1500/107 V　　　[OR 14.0 V]

For R3, R4 and R5
V3 = V4 = V5 = (20 - 1500/107)V = 640/107 V　　　　　　　[OR 5.98 V]

(c)
For R5 (20R)
I5 = (32 / 107R) A
V5 = 640/107 V
By P = IV
P = (32 / 107R) (640/107)
　= (20480 / 11449R) W　　　　　　　[OR (1.79/R) W]

#2係對的
只係佢計左(b) part先計(a) part
不過唔知點解佢多左個30R出黎