# The internal resistance of battery and dc generator - help, I'm stuck.

Discussion in 'Homework Help' started by Christine Grech, May 31, 2015.

1. ### Christine Grech Thread Starter New Member

May 31, 2015
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0
I need to solve this, but I need help...

'A battery having an emf of 105V and an internal resistance of 1 Ohm is connected in parallel with a d.c generator of emf 110V and internal resistance of 0.5 Ohm to supply a load having a resistance of 8 Ohms. Calculate: a) the currents in the battery, the generator and the load; b) the potential difference across the load.'

For question number a), is it right if I use 'V=Emf-Ir' please?

2. ### LDC3 Active Member

Apr 27, 2013
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161
A good place to start is to draw a diagram with the 2 voltage sources and the 3 resistances.

3. ### shteii01 AAC Fanatic!

Feb 19, 2010
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^ what he said.

4. ### Christine Grech Thread Starter New Member

May 31, 2015
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I did draw it. Can you please tell me if V = Emf - Ir is the right equation to use for question number a)? Thank you.

5. ### LDC3 Active Member

Apr 27, 2013
920
161
If both positive terminals of the voltage sources are connected together, than that equation only tells you the voltage across the battery, not the voltage across the load.

6. ### Christine Grech Thread Starter New Member

May 31, 2015
6
0
Ok so it is wrong, thank you.

Apr 5, 2008
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Hello,

As asked, post your schematic here, so we can have a look you made a correct one.
You can do this using the "Upload a File" button below the reply box.

Bertus

8. ### shteii01 AAC Fanatic!

Feb 19, 2010
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Part a asks you to find 3 things. To find 3 things, you need 3 equations.

9. ### ericgibbs AAC Fanatic!

Jan 29, 2010
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Hi CG,

EMF is the open circuit voltage, so the V will be EMF - Iamp

But more maths are required to solve the problem.
E

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10. ### Lestraveled Well-Known Member

May 19, 2014
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Sounds like a job for Kirchoff's laws.

Feb 19, 2010
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yep

12. ### Christine Grech Thread Starter New Member

May 31, 2015
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Oh, ok so I have to use Kirchoff's law. Thank you all. Also, thank you ericgibbs, for your diagram as I had drawn it in a different way, and did not realise what equation to use.

13. ### shteii01 AAC Fanatic!

Feb 19, 2010
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How do you know that their's is right?

14. ### ericgibbs AAC Fanatic!

Jan 29, 2010
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Who is theirs.???
Mine or the OP's.

My drawing was created from the very clear description posted by the OP.

15. ### shteii01 AAC Fanatic!

Feb 19, 2010
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OP did not post any drawing or schematic.

Jan 29, 2010
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May 31, 2015
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18. ### ericgibbs AAC Fanatic!

Jan 29, 2010
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In the Top menu bar of this page , is an option named Text books, click and find the topic that you need help with.
E

19. ### JoeJester AAC Fanatic!

Apr 26, 2005
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I found it easier to use the Norton equivalent of the two sources and then find the equivalent resistance of the internals and the load.

May 31, 2015
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Thank you.