Solve Combination Circuit Homework: Req, IT, Current & Voltage

In summary, the problem involves determining Req, IT, and the current and voltage across each resistor in a circuit. The aim is to collapse the multiple drawings into one resistor that equals Req and find the total power used by the circuit. The equations used are Req = R1+R2+R3..., 1/Req = 1/R1+1/R2+1/R3..., V = IR, and P = IV. The solution involves combining resistors BC and EFG in parallel, and then dealing with a few series resistors A and D. The mistake was treating BC and F as parallel resistors instead of combining E, F, and G in series.
  • #1
dropgigawatt
10
0

Homework Statement



Determine the Req, IT, and the current and voltage across each resistor. Collapse each drawing into one resistor that equals Req. Find the total power used by the circuit. Also determine the voltage, current, and power for each individual resistor.

The one I'm having trouble with:
pAfgQsr.jpg


Homework Equations



Req = R1+R2+R3...
1/Req = 1/R1+1/R2+1/R3...
V = IR
P = IV

The Attempt at a Solution



I combined B and C into BC (4 Ω) and then combined that with F to make BCF (2 Ω). This would give me the following resistances: RA = 2 Ω, RE = 6 Ω, RBCF = 2 Ω, RG = 2 Ω, and RD = 5 Ω. That would make Req = 17 Ω since all these are now in series.

When trying to calculate the current of the whole circuit... I = V/Req = 40/17 = 2.35 A

My teacher posted that the total current should be 4 A. I'm not sure where I messed up.
 
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  • #2
dropgigawatt said:

Homework Statement



Determine the Req, IT, and the current and voltage across each resistor. Collapse each drawing into one resistor that equals Req. Find the total power used by the circuit. Also determine the voltage, current, and power for each individual resistor.

The one I'm having trouble with:
pAfgQsr.jpg


Homework Equations



Req = R1+R2+R3...
1/Req = 1/R1+1/R2+1/R3...
V = IR
P = IV

The Attempt at a Solution



I combined B and C into BC (4 Ω)
That's a fair start. :approve:

and then combined that with F to make BCF (2 Ω).
There is where the problem is!

You can't treat BC and F as being parallel with each other. There are resistors E and G in the way which prohibit that!

However, what you can do is combine E, F and G, all in series.

After that, you have parallel resistors that you can combine: BC and EFG. (And then deal with a couple more series resistors A and D even after that.)
 
  • #3
AH! That makes so much sense! Thanks!
 

1. What is Req in a combination circuit?

Req, or equivalent resistance, is the single resistance value that could replace all the resistors in a combination circuit while maintaining the same current and voltage values. It is calculated using the formula 1/Req = 1/R1 + 1/R2 + 1/R3 + ..., where R1, R2, R3, etc. are the individual resistances in the circuit.

2. How do you calculate the total current in a combination circuit?

The total current in a combination circuit is equal to the sum of the individual branch currents. This can be calculated using Ohm's Law, where current (I) is equal to voltage (V) divided by resistance (R), or I = V/R.

3. What is the relationship between voltage and resistance in a combination circuit?

In a combination circuit, the voltage across each resistor is equal to the total voltage of the circuit. The relationship between voltage and resistance is directly proportional, meaning that as resistance increases, voltage decreases, and vice versa.

4. How can you simplify a combination circuit?

A combination circuit can be simplified by using equivalent resistance (Req) and applying series and parallel circuit rules. Start by replacing any series or parallel resistors with their equivalent value, then use the equivalent resistance to calculate the total current and voltage in the circuit.

5. What is the difference between series and parallel circuits?

In a series circuit, all components are connected one after the other, creating a single pathway for current to flow through. In a parallel circuit, the components are connected in separate branches, providing multiple pathways for current to flow. This results in different voltage and current values in each type of circuit.

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