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# Circuit table calculations question watch

1. I received homework to complete 4 tables, Ive already done 3 but got stuck on this one. I have no clue what to do: http://imgur.com/KhixzAF
2. (Original post by LPLunaticFringe)
I received homework to complete 4 tables, Ive already done 3 but got stuck on this one. I have no clue what to do: http://imgur.com/KhixzAF
Can't see which is V1 and V2 in the diagram...

it looks like I3 should be equal to I1+I2 due to Kirchoff's current law, which unfortunately mean you need to have another look at that tho.

there seems to be enough to go on e.g. Row 5 gives you a value for the resistance of R2+R3 combined and R3 separately... the value of R2 can't be a secret for long.
3. (Original post by Joinedup)
Can't see which is V1 and V2 in the diagram...

it looks like I3 should be equal to I1+I2 due to Kirchoff's current law, which unfortunately mean you need to have another look at that tho.

there seems to be enough to go on e.g. Row 5 gives you a value for the resistance of R2+R3 combined and R3 separately... the value of R2 can't be a secret for long.
Sorry that it took so long. This is how the circuit looks like and I have edited the table to follow Kirchoff's law of I1 + I2 = I3 for the known values.
4. (Original post by LPLunaticFringe)
Sorry that it took so long. This is how the circuit looks like and I have edited the table to follow Kirchoff's law of I1 + I2 = I3 for the known values.

Look at the first line of the table:

Correct:

The total voltage of V1 + V2 = 2 + 2 = 4V is applied across R1 = 20 ohms which you correctly calculated the current I1 as 0.2A.

The series combination of R2 and R3 (series resistances sum) = 10 + 10 = 20 ohms, which is also correct.

Mistake:

Notice though, that the total voltage (4V) is also applied to the series combination of R2 + R3 = 20 ohms.

I2 must flow through both of these components. Hence the current I2 = Vtotal/Rseries = (2 + 2)/(10 + 10) = 4/20 = 0.2A

Which makes the current I3 = I1 + I2 = 0.2 + 0.3 = 0.4A

You have made similar errors in the next two rows.

The fourth row is correct so far, you can now easily fill in the value of I3

The fifth row is correct so far.

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