Analyzing Electric Circuits: Homework Help

[MsHomework]

Homework Statement

[attachment]

Homework Equations

I=V/R V=R*I R=V/I R_series = R₁ + R₂ + R₃ ...
1/R_parallel = 1/R₁ + 1/R₂ + 1/R₃ ...
Kirchhoff Law

The Attempt at a Solution

R_source = V_source/I_source
R_source = 50/0.25
R_source = 200Ω

I don't know what to do next!

 

[MsHomework]

Anyone... Please help! I have tried so many times to figure this out but I can't! A hint my teacher gave me is to figure out the R₄

 

[berkeman]

Homework Statement

[attachment]

Homework Equations

I=V/R V=R*I R=V/I R_series = R₁ + R₂ + R₃ ...
1/R_parallel = 1/R₁ + 1/R₂ + 1/R₃ ...
Kirchhoff Law

The Attempt at a Solution

R_source = V_source/I_source
R_source = 50/0.25
R_source = 200Ω

I don't know what to do next!

Ground the bottom of the voltage source and write the KCL at the node between the left resistor and the right parallel resistors. What does that equation do for you?

 

[MsHomework]

How do I ground it! I did not learn that...

 

[berkeman]

How do I ground it! I did not learn that...

It just means draw a little ground symbol on that bottom wire, to indicate that you are considering it to be the zero volts potential for the circuit. That way your voltage source output is the value of the source (since it is referenced to zero volts). You could arbitrarily set the bottom of the voltage source to something else like "10 volts", but that just introduces extra complexity into the KCL.

 

[MsHomework]

64. (a) R4 5 2.50 x 10²
I1 = 0.250 A
I2 = 0.150 A
I4 = 0.100 A
(b) V2 = 16.7 V
V3 = 8.30 V

This is the answer from the back of the textbook... Also my teacher said to use the basics aka... I am not suppose to ground!

 

[berkeman]

64. (a) R4 5 2.50 x 10²
I1 = 0.250 A
I2 = 0.150 A
I4 = 0.100 A
(b) V2 = 16.7 V
V3 = 8.30 V

This is the answer from the back of the textbook... Also my teacher said to use the basics aka... I am not suppose to ground!

Okay, no problemo. Nothing fancy.

Just label that bottom wire with "0 volts", and write the one KCL equation for the top middle node. Simple!

 

[MsHomework]

Can you show me step by step, because I still am confused!

 

[berkeman]

Can you show me step by step, because I still am confused!

No, sorry, that's now how we handle Homework Help at the PF (which you know).

Tell us how to write KCL (Kirchoff's Current Law) equations. Then write the KCL for the node in the middle of the upper branch as I mentioned several times already.

http://www.wiziq.com/tutorial/32583-Solving-problems-using-Kirchoff-s-Law-I

.

 

[MsHomework]

Just a quick question, How come you have to put 0 volts at the bottom in the parallel...

 

[berkeman]

Just a quick question, How come you have to put 0 volts at the bottom in the parallel...

With the KCL, you will write the sum of all currents leaving that central node = 0 (amps or milliamps). When you write the currents as V/R for each branch, the delta-V is the voltage at the node minus the voltage at the node on the other side of the resistance. If you label the bottom wire as 0 volts, then that second voltage in the subtraction goes away in the equation (because it is 0). It's mostly a convenience thing for writing the KCL equations -- pick a logical node to label as 0 volts before starting to write out the KCL equation(s).

If a node is already labeled with a ground symbol in a schematic, you automatically take that node as being at 0 volts.

Can you take a cut at writing the KCL at that node now?

 

[MsHomework]

I am sorry, but I personally feel more confused! I don`t feel that you are helping me as much. Thank you for trying to help!