Electric Circuit Help (Emf and Internal Resistance)

  • #1
1. Find the current in, and the potential difference across, each resistor in the circuit shown below:

The circuit is a simple parallel circuit with 2.0 ohms at the first resistor, 10.0 ohms at the second, and 20.0 ohms at the third

The problem also gives you Emf which is 12.0 V and the internal resistance "r" which is 0 ohms




2. Voltage = Current*Resistance
Possibly: Voltage = Emf - Current*Resistance
Req (total resistance) = [(1/Resistance 1) + (1/Resistance 2) + (1/Resistance 3)]-1




3. I would attempt the problem but I've tried so many times and I'm just lost. I was absent the day this question was answered in class.

I thought you were supposed to find the Req first then use the voltage given to find the current in the system, but thats not helping me at all. I don't understand Emf or internal resistance so I'm not sure of its purpose.


I hope this helps. I'm on a laptop so I can't scan any images at all.
 

Answers and Replies

  • #2
stewartcs
Science Advisor
2,177
3
In parallel circuits the voltage through each branch is the same. Use Ohm's Law to find the current.
 
  • #3
338
0
2. Voltage = Current*Resistance
Possibly: Voltage = Emf - Current*Resistance
Req (total resistance) = [(1/Resistance 1) + (1/Resistance 2) + (1/Resistance 3)]-1
I don't believe that's correct.

[tex]\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_2}[/tex]

[tex]R_{eq}=\frac{R_1 R_2 R_3}{R_1 R_2 + R_1 R_3 + R_2 R_3}[/tex]

This isn't really needed to find the current through each resistor.

Ohm's law, applied in this case:

[tex]V = I_1 R_1 = I_2 R_2 = I_3 R_3[/tex]

Therefore...

[tex]I_1=\frac{V}{R_1}[/tex]
[tex]I_2=\frac{V}{R_2}[/tex]
[tex]I_3=\frac{V}{R_3}[/tex]

You can use [tex]R_{eq}[/tex] to see if you got it right...

[tex]V=I R_{eq}[/tex]
[tex]I=\frac{V}{R_{eq}}=V\frac{R_1 R_2 + R_1 R_3 + R_2 R_3}{R_1 R_2 R_3}[/tex]

and...

[tex]I = I_1 + I_2 + I_3[/tex]
 
Last edited:

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