Hi,
I'm having trouble with these two circuit analysis problems.
I understand I need to use KCL, KVL and Ohms law to relate the voltage, amps and resistance in order to solve for the required variables.
However, I can't seem to connect the dots, every equation I write seems to need me to solve another equation first.

Any help would be appreciated. Thanks.

 

I dont know what KCL and KVL are. For the first circuit start by working out the effective resistace across the voltage source from the combination of resistors in serial and parallel. You should be able to continue from there.
For circuit 2 start by calculating the value of R2. The 40 ohm resistor and R2 form a simple potential divider. Then calculate the effective source resistance between a and b. You then have another potential divider formed with the source resistance.

Les.

 

I dont know what KCL and KVL are. For the first circuit start by working out the effective resistace across the voltage source from the combination of resistors in serial and parallel. You should be able to continue from there.
For circuit 2 start by calculating the value of R2. The 40 ohm resistor and R2 form a simple potential divider. Then calculate the effective source resistance between a and b. You then have another potential divider formed with the source resistance.

Les.

KVL = Kirchoff's Voltage Law: The sum of the voltage drops around a closed loop is 0
KCL = Kirchoff's Current Law: The sum of the currents into a node is 0

 

Hi,
I'm having trouble with these two circuit analysis problems.
I understand I need to use KCL, KVL and Ohms law to relate the voltage, amps and resistance in order to solve for the required variables.
However, I can't seem to connect the dots, every equation I write seems to need me to solve another equation first.

Any help would be appreciated. Thanks.

View attachment 132679

It's hard to help you find and get past the trouble you are having until you show your best attempt to work the problems.

 

For the second problem, I realised the 40 ohms resistor had to drop the current by 16 to get 4, allowing me to solve R1 as 10ohms and RL as 8ohms.

I'm still having trouble with problem 1 though. The second voltage is tripping me up.
I tried summing up the equivalent resistance through the 1/(1/R1+1/R2) formula resulting in 37ohms and multiplying by 25A to get voltage.
However this isn't the correct answer. Is that second voltage asking for the voltage absorbed by the 30 and 60 ohm resistors or is it a separate connection in the middle?

For my Req calculation I combined the
parallel 30 + 60 resistors
resulting 20 + 30 series
resulting 50 + 75 parallel
resulting 25 + 12 series

 

Ah. In reading that i realised I calculated 75/2.5 as 25 when it's 30.
42ohms*25Amps = 1050 which is the correct answer. 15Amps*20ohms = 300V for V2

Thanks for the help.

 

For the second problem, I realised the 40 ohms resistor had to drop the current by 16 to get 4, allowing me to solve R1 as 10ohms and RL as 8ohms.

The 40 Ω resistor drops the VOLTAGE by 16 V to leave you with 4 V across R2 (when Rl is removed). It doesn't drop the current.

I'm still having trouble with problem 1 though. The second voltage is tripping me up.
I tried summing up the equivalent resistance through the 1/(1/R1+1/R2) formula resulting in 37ohms and multiplying by 25A to get voltage.
However this isn't the correct answer. Is that second voltage asking for the voltage absorbed by the 30 and 60 ohm resistors or is it a separate connection in the middle?

For my Req calculation I combined the
parallel 30 + 60 resistors
resulting 20 + 30 series
resulting 50 + 75 parallel
resulting 25 + 12 series

Start always asking if the answer makes sense. When you parallel two resistors of equal size, you know that the result is half the resistance. So if you get a result that says that a 50 Ω resistor in parallel with a 75 Ω resistor is 25 Ω, a red flag should go up that something is wrong.

We all make silly math or reasoning mistakes on a pretty frequent basis, so one of the best skills you can develop is the ability to check your work as you go along. It will make both finding and fixing errors a lot easier. You also need to start using and properly tracking your units.