Class Activity (week 1)

Figure 1

1) What will happen when the switch is turned on (Fig 1)?

If V1 = V2 and R1 = R2 so Va = Vb. So if the switch turn on or turn of there is no current in light bulb 3. Therefore, the bright of two light bulbs do not change.

I = (V1 + V2)/(R1 + R2) , Va + V1 - R1*I = Vb , If V1 = V2
so V1 - R1*I = 0
Then Va = Vb











2) What will happen when the switch is turn on (Fig 2)?

Suppose V1 = V2 = V3 and R1 = R2
When switch is open:
I = (V1 + V2)/(R1 + R2) , I = V1/R1 , Also Vab = R1*I , so Vab = R1*(V1/R1) = V1
Similarly Vbc = R2*I = V1.
If switch turn on V3 will be parallel with light bulb 1 and V3 is equal V1. Therefore, the bright of two light bulb 1 and 2 do not change.

Figure 2