Using complex numbers to solve for a current in this circuit

[GJ1]

This was not a homework assignment, it's not necessary to understand the equation for this course, I was just interested in how they derived their answer.

 

[FactChecker]

This was not a homework assignment, it's not necessary to understand the equation for this course, I was just interested in how they derived their answer.

I should have said that we are only supposed to give hints and directions in a homework type of question. I think you should give it another try using the hint in my post #30 above.

 

[Mark44]

50/[(4+3j)x50+100]x150=20-10j

Although you have parentheses and brackets in your work, you don't have enough of them.

50/[(4+3j)x50+100]x150 means this:
$$\frac{50}{(4 + 3j) \cdot 50 + 100} \cdot 150$$
The above equals $$\frac {7500}{(4 + 3j) \cdot 50 + 100}$$
and does not equal 20 - 10j.

 

[PeroK]

50/[(4+3j)x50+100]x150 means this:
$$\frac{50}{(4 + 3j) \cdot 50 + 100} \cdot 150$$
The above equals $$\frac {7500}{(4 + 3j) \cdot 50 + 100}$$
and does not equal 20 - 10j.

And yet:
$$\bigg [\frac{50}{(4 + j3)(50) + 100} \bigg ] \times 150 = \frac{150}{(4 + j3) + 2}= \frac{50}{2+ j} = \frac{(50)(2 - j)}{5} = 20 - j10 $$

 

[GJ1]

Can you just explain how you get 50/2+j from 150/(4+j)+2

 

[FactChecker]

Can you just explain how you get 50/2+j from 150/(4+j)+2

He doesn't. He gets 50/(2+j) from 150/( (4+j3)+2 ).
Please use parenthesis to make your math expressions clear.

This is not just a picky complaint. In these days of computers and calculators, they will always give you the wrong answer if the parenthesis are wrong.

 

[GJ1]

Just got it. Thanks for explaining it with your example. Greatly appreciated!!!!!

 

[Mark44]

And yet:
$$\bigg [\frac{50}{(4 + j3)(50) + 100} \bigg ] \times 150 = \frac{150}{(4 + j3) + 2}= \frac{50}{2+ j} = \frac{(50)(2 - j)}{5} = 20 - j10 $$

I stand corrected.

 

[GJ1]

He doesn't. He gets 50/(2+j) from 150/( (4+j3)+2 ).
Please use parenthesis to make your math expressions clear.

This is not just a picky complaint. In these days of computers and calculators, they will always give you the wrong answer if the parenthesis are wrong.

Understood

 

[PeroK]

I stand corrected.

And now the OP has what he wanted. A solution on a plate!

 

[FactChecker]

And now the OP has what he wanted. A solution on a plate!

Right. But it won't go very far unless the OP has learned from this thread. Still, we should be careful to not give in to frustration and just give the answer.

 

[berkeman]

Right. But it won't go very far unless the OP has learned from this thread.

We could give them a similar complex number manipulation question to test their understanding. Any volunteers?

 

[scottdave]

It's (50/(4+j3)(50)

Those parentheses do not match up. You are missing a "closing paren" somewhere. I'm having a little trouble guessing what the 50 over (4+j3) represents. What about the second 50? Some units would be nice.