# Voltage and current calculation of circuit

• Engineering
• PhysicsTest
In summary: I3)*1500- (I2-I3)*2200=0-15000+1500*I3-2200*I2+2200*I3=0-15000-2200*I2+3700*I3=0In summary, the current source is turned around so the loop current flows in the opposite direction.

#### PhysicsTest

Homework Statement
Need to calculate the voltage and current for a circuit
Relevant Equations
KCL and KVL equations , V=IR
I am trying to find voltages and currents of the below circuit,

3.3 -22000*I2 - 2200(I2-I3) = 0
3.3 -24200*I2 + 2200*I3 = 0 -> eq1

-(10 - I3)*1500 - (I2 - I3)*2200 = 0
-15000 + 1500*I3 - 2200*I2 + 2200*I3=0
-15000 - 2200*I2 + 3700*I3=0 -> eq2

Solving equations 1 and 2 i get I2=0.38 Amps and I3 = 4.28 Amps

I assume i have completely gone wrong in calculations, can current I3 flow into the source. Please help.

#### Attachments

• cur2.txt
1.1 KB · Views: 60
If current 10 Amps flows through R3 then the voltage at vout1 shall be 1.5K*10 Volts = 15K volts, but if i see the simulation results it shows 20K Volts

It is all confusion.

Replace your .Transient analysis with a .DC operating point analysis. That will give you the voltages at all nodes and the currents in all components.

You may have to turn a passive component around to get that loop current flowing with the correct sign in the .DC report.

The arrow on the current source is conventional current. Your I3 arrow is in the opposite direction, which makes visualisation of the current flow more difficult.

You can replace R3 with a short circuit because it is in series with a current source.

Baluncore said:
You can replace R3 with a short circuit because it is in series with a current source.
This helped me to solve the problem
The updated circuit is

3.3 - 22000*I2 -2200*(10+I2) = 0
solving I2 = -0.90 Amps
Vout1=20K Volts it matches with the simulation results
--- Operating Point ---

V(n001): 3.3 voltage
V(vout1): 20000.3 voltage
I(I1): 10 device_current
I(R2): 9.09105 device_current
I(R1): -0.908955 device_current
I(V1): 0.908955 device_current

Still my question is why do i need to remove R3 to get result?

PhysicsTest said:
If current 10 Amps flows through R3 then the voltage at vout1 shall be 1.5K*10 Volts = 15K volts, but if i see the simulation results it shows 20K Volts
I think you were assuming the voltage across the current source was zero.
You were looking at the 10 amp through the 1k5 when it actually flows through the Thevenin resistance of Vout.

Another way to analyse it:
Node(2) has Thevenin resistance; Rth = (22k//2k2) = 2k000
3.3V * 2k2 / ( 22k + 2k2 ) = +0.300 volt;
Then add the (10A * 2k000) = 2000V;
To get node(Vout1), V(out) = +2000.300 V.

PhysicsTest
If you would change your sign for loop2 like Baluncore wrote, I think you would arrive at the solution. The current source being in the positive direction.

(10-I3)*1500 + (I2-I3)*2200=0

## 1. What is the relationship between voltage and current in a circuit?

The relationship between voltage and current in a circuit is described by Ohm's Law, which states that the current flowing through a circuit is directly proportional to the voltage and inversely proportional to the resistance. This can be expressed as I = V/R, where I is the current in amperes, V is the voltage in volts, and R is the resistance in ohms.

## 2. How do you calculate the voltage in a circuit?

To calculate the voltage in a circuit, you can use Ohm's Law and rearrange the equation to solve for voltage. This would be expressed as V = IR, where V is the voltage, I is the current, and R is the resistance. You can also use Kirchhoff's Voltage Law, which states that the sum of all voltage drops in a closed loop circuit is equal to the sum of all voltage sources.

## 3. How do you calculate the current in a circuit?

The current in a circuit can be calculated using Ohm's Law, which states that the current is equal to the voltage divided by the resistance. This can be expressed as I = V/R, where I is the current, V is the voltage, and R is the resistance. You can also use Kirchhoff's Current Law, which states that the sum of all currents entering a node in a circuit is equal to the sum of all currents leaving that node.

## 4. How does the resistance affect the voltage and current in a circuit?

The resistance in a circuit affects the voltage and current by limiting the flow of electrons. A higher resistance will result in a lower current, as there is more resistance for the electrons to overcome. This also means that the voltage will be higher, as the electrons have to work harder to overcome the resistance. On the other hand, a lower resistance will result in a higher current and a lower voltage.

## 5. How do you calculate the power in a circuit?

The power in a circuit can be calculated using the formula P = VI, where P is the power in watts, V is the voltage in volts, and I is the current in amperes. This formula can also be expressed as P = I^2 * R or P = V^2 / R, depending on the given values. Power is a measure of the rate at which energy is being transferred in a circuit.