- #1
kamhogo
- 86
- 6
Homework Statement
There are 5 identical bulbs. All are glowing. Rank from brightest to dimmest. Some may be equal.
Homework Equations
I= (ΔV)/R
Req = [(1/R1)+ (1/R2) +...]^-1 (Parallel resistors; same delta V)
Req = R1 + R2 + ... ( Series resistors; same current I)
The Attempt at a Solution
Let all the bulbs have resistance R.
A. Combine bulbs R and S ( parallel, same ΔV)
Req = [(1/R)+(1/R)]^-1 = R/2
B. Combine R&S with P and T ( series, same I )
Req = (R/2) + R + R = 2.5 R
C. Combine (R&S, P, T) with Q ( Parallel, same ΔV)
Req = [(1/R)+(1/2.5R)]^-1 = 0.71R
ΔV = ε- - > I = ε/Req = 1.4ε/R
Now decompose to find individual currents:
A. R(Q) = R; ΔV = ε --> I(Q) = ε/R
R(R&S, P, T) = 2.5R --> I (R&S, P, T) = 0.4ε/R
I (P) = I (T) = 0.4ε/R
R(R&S)= R/2
ΔV (R&S) =( 0.4ε/R)*(R/2)= 0.2 ε
ΔV (R) = ΔV (S) = 0.2ε
R (S) = R (R) = R
I (S) = I ( R) = 0.2ε/R
⇒Q >P=T >S =R
This is incorrect t and I'd like to know what I did wrong. thanks in advance for any help.