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Calculating "Lost volts"

  1. Mar 20, 2017 #1
    1. The problem statement, all variables and given/known data
    A cell has an e.m.f =1.5v and Internal Resistance = 0.75Ω is connected as shown in the following circuit ( circuit has 3Ω resistor under the battery)

    (I) Calculate the reading on the voltmeter.
    (Ii) what is the value of the "lost volts" in this circuit?

    Can anyone help me? I don't n ow the equation.

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Mar 20, 2017 #2


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    Staff: Mentor

    Hello Ellie4700,

    The forum rules require that you show some attempt at a solution before help can be offered. Look in your course notes and textbook in the relevant section in order to find equations that might pertain to this topic.

    You might also want to upload the image so that the placement of the voltmeter referred to can be seen.
  4. Mar 20, 2017 #3


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    Homework Helper
    Gold Member

    The relevant equation that you are looking for is Ohm's Law. You can treat the internal resistance as an actual resistor which is inside the battery cell. This resistance is in series with the voltage source and the rest of the external circuit. That should help you get started.
  5. Mar 20, 2017 #4
    Thanks for the reply. I had a look and I still can't find any relevant equations to use. If I had an equation I would be able to work it out from there. I tried to upload a photo but it kept denying me.
  6. Mar 20, 2017 #5
    Thanks. I'll give it a try.
  7. Mar 20, 2017 #6


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    Staff: Mentor

    What circuit laws have you studied?

    It may be that you need to accumulate a few more posts before the forum software will let you post images (it's an anti-spam "feature" that's built in). Perhaps your circuit looks something like this:

  8. Mar 20, 2017 #7
    The diagram looks exactly like that. I live in Scotland and the course work is a bit different. I am doing higher physics and the key area is called Electrical Sources and Internal Resistance.
  9. Mar 20, 2017 #8


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    Staff: Mentor

    Okay. You'll want to review/investigate Kirchhoff's circuit laws (KCL and KVL), and Ohm's law. For this problem in particular you can make do with Ohm's law as @scottdave suggested. Start by finding the current ##I##.
  10. Mar 20, 2017 #9
    Thank for the help. I'll give it a try :smile:
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