Consider the circuit given below: a)What is the voltage at point A? b)What is th

Question

Consider the circuit given below:

a)What is the voltage at point A?

b)What is the voltage at point B?

c)If I give you that the voltage at point C is 8V, what is the current thorough R1?

d)If I give you that the voltage at point C is 8V, what is the current thorough R2?

e)Given your understanding of the fact that R1 and R2 are in series, does it make sense to you that the voltage at point C is 8V? In other words, would you have agreed with me if I said that voltage at point C is 9V? Justify your answer

Explanation / Answer

(a and b )

all three branches are in parallel .

so Potential difference across each branch will be same.

PD across R1R2 branch = PD across R3R4 branch = 12 V

so Va - Vb = 12 V

suppose lower branch is at zero voltage say Vb = 0

then Va = 12 V

c)PD across R1 = Va - Vc = 12 - 8 = 4 volt

current through R1 = 4 / 10 = 0.4 A

d) PD across R2 = Vc - Vb = 8 - 0 = 8 volt

current through r2 = 8 / 20 = 0.4 A

e) PD across combination of R1 and R2 is 12 V.

current through series element will be same say i1.

then i1R1 + i1R2 = 12

i1 = 12 / (R1 + R2) = 12/30 = 0.4 A

PD across R1 = 0.4 x 10 = 4 V

PD across R2 = 0.4 x 20 = 8 V

b point was at zero (assumed) so Vc = 8 - 0 = 8 v

if Vc = 9 V given

and PD across R2 : Vc - Vb = 8 V

9 - Vb = 8

Vb = 1 V

(initially we assumed that lower branch , point B, was at zero then Vc was 8V)

now if we take Vb = 1 V then Vc will be 9V.

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