Help with Electricity Assignment: Vt, It, I1, I2

[jam7cacci]

[SOLVED] Electricity - i need help

hi! I need some assistance regarding my assignment. hope there's anyone who could help me out. the questions are:

1.a. a 12 ohms resistor is connected in parallel with a series combination of resistors of 8 ohms and 16 ohms. if voltage drop across the 8 ohms resistor, is 48 volts. Determine the total impressed voltage and total current. Vt=? It=?



1.b. Relevant equations
V = IR; I=V/R



1.c. The attempt at a solution
so... first i have to get the total resistance to get the total current and voltage right? (Please correct me if I'm wrong. thanks! :D)

R12 = 8ohms + 16ohms = 24ohms

1/RT = 1/R12 + 1/R3
1/RT = 1/24 + 1/12ohms
1/RT = 1/8 ohms

Rt = 8 ohms


<i> here's the part where I'm totally confused </i>
It = Vt/Rt
It = 48Volts / 8 ohms
It = 6 A

Vt = 48? (i really don't know how to solve for the total voltage)



2.a. 2 resistors 1.95ohms and 0.05ohms are connected in parallel and takes a total current of 50V. What is the current in each resistor?



2.b. Relevant equations
I1 = It

I1 = V1/R1



2.c. The attempt at a solution

I1 = 50V / 1.95ohms
I1 = 25.64 A

I2 = 50V / 0.05ohms
I2 = 1000 A

 

[Hootenanny]

With regards to the first question all you need to do is apply Kirchoff's laws.

 

[malty]

hi! I need some assistance regarding my assignment. hope there's anyone who could help me out. the questions are:

1.a. a 12 ohms resistor is connected in parallel with a series combination of resistors of 8 ohms and 16 ohms. if voltage drop across the 8 ohms resistor, is 48 volts. Determine the total impressed voltage and total current. Vt=? It=?



1.b. Relevant equations
V = IR; I=V/R



1.c. The attempt at a solution
so... first i have to get the total resistance to get the total current and voltage right? (Please correct me if I'm wrong. thanks! :D)

R12 = 8ohms + 16ohms = 24ohms

1/RT = 1/R12 + 1/R3
1/RT = 1/24 + 1/12ohms
1/RT = 1/8 ohms

Rt = 8 ohms

That looks Right
<i> here's the part where I'm totally confused </i>
It = Vt/Rt If you're t subscript is referring to the total current/voltage then this is wrong
It = 48Volts / 8 ohms
It = 6 A

Vt = 48? (i really don't know how to solve for the total voltage)



2.a. 2 resistors 1.95ohms and 0.05ohms are connected in parallel and takes a total current of 50V. What is the current in each resistor?

This part looks fine

2.b. Relevant equations
I1 = It

I1 = V1/R1



2.c. The attempt at a solution

I1 = 50V / 1.95ohms
I1 = 25.64 A

I2 = 50V / 0.05ohms
I2 = 1000 A

For part (a) you are giving the voltage across one resistor, that is in series with another resistor.. what can you say about the current through both resistors??

 

[jam7cacci]

For part (a) you are giving the voltage across one resistor, that is in series with another resistor.. what can you say about the current through both resistors??

first of all, i want to say thank you for helping me out. but honestly, I'm really am having big problems when it comes to getting the total current or total voltage...

with regards to your question... hmmm...

current through the both resistor in question 1.a

the one that is in series which is the 8 and 16 their current is 2A

and the one that is in parallel which is 12 ohms is 4A

i used the formula I = E/R

whew... i hope this is right...

 

[malty]

first of all, i want to say thank you for helping me out. but honestly, I'm really am having big problems when it comes to getting the total current or total voltage...

with regards to your question... hmmm...

current through the both resistor in question 1.a

the one that is in series which is the 8 and 16 their current is 2A

and the one that is in parallel which is 12 ohms is 4A

i used the formula I = E/R

whew... i hope this is right...

No I don't think it is, sorry.


Hootenanny mention Kirchoff Laws, one of them states that the sum of the currents entering a node MUST equal the sum of the currents exiting the node... so in your answer you're saying that the current through the series (8ohm and 16 ohm) part is 2A, yet in you're first attempt you said the current through the (8 Ohm) resistor was 6A.. hopefully you see something wrong with this!

If you wouldn't mind showing us how you calculated the 2A and 4A values. .

Remember the 48V is supplied across the 8ohm resistor in the series, this is NOT the total voltage across the entire circuit!

 

[jam7cacci]

No I don't think it is, sorry.


Hootenanny mention Kirchoff Laws, one of them states that the sum of the currents entering a node MUST equal the sum of the currents exiting the node... so in your answer you're saying that the current through the series (8ohm and 16 ohm) part is 2A, yet in you're first attempt you said the current through the (8 Ohm) resistor was 6A.. hopefully you see something wrong with this!

If you wouldn't mind showing us how you calculated the 2A and 4A values. .

Remember the 48V is supplied across the 8ohm resistor in the series, this is NOT the total voltage across the entire circuit!

whew... just like what i posted before I'm really am having a hard time understanding this that's why i have to repeat this subject

anywayz... here's how i calculated it

48V / 12ohms = 4A

i really can't solve it... i don't know how i got the 2A anymore... sorry... I'm really am a slow learner when it comes to physics. its like the subject hates me. sorry...

 

[Hootenanny]

Firstly, can you calculate the current through the 8ohm resistor and secondly, what do you know about the current through two resistors in series? [You must have learn this result in class]

 

[jam7cacci]

Firstly, can you calculate the current through the 8ohm resistor and secondly, what do you know about the current through two resistors in series? [You must have learn this result in class]

this is what i know...

first i have to get the total resistance...
so in series i just have to add them up. with parallel i add them like this 1/R1 + ...+1/Rn

then the total current...
which is It = Vt / Rt

getting the current one by one is the one i really don't understand at all. Anywayz, i have passed my assignment already... so i can't undo it anymore...

thanks for all the help... i tried to attempt to do what you've told me to do but i just don't understand it. i tried to check some in the net but it made me more confused...

i just hope that my prof will just passed me by being a good kid. hahaha... since Christmas is near.

 

[Hootenanny]

Passing the course isn't everything. Just encase you want to work through the problem, the current through both of the resistors will be the same.

 

[bsimmo]

Draw the circuit and put the values in

---\/\8/\-----\/\16\/\-----
 |                     |
  -------\/\12/\--------

Work out the current through the 8Ω first.
You are given the voltage (48V) that this uses. So your answer to I=V/R is the current through this resistor alone.

Then you need to work out (maybe you already have this answer... in front of you) what current goes through the 16Ω resistor, one you have that you can work out the voltage it uses.
Then you need figure out how to work out the voltage through the 12Ω... to get the current through the 12Ω resistor.
Then lastley get total voltage and total current...
(hint if you have 3 wires a,b,c all connected together at one point. Ia + Ib = Ic)