Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Very basic Physics questions!

  1. Sep 13, 2010 #1
    Might be some simple questions for you guys but I'm just in grade 9

    1. Do isolating transformers change the voltage in a circuit?

    What I know is that isolating transformers have the same amount of coils because it needs to be safe.

    2. Explain why an isolating transformer is often used in a bathroom shaver circuit.

    3. A transformer has 5000 tunrs on its primary coil, and 8000 tunrs on its secondary coil.
    If the input voltage is 230 V, find the output voltage.

    - Lit
  2. jcsd
  3. Sep 13, 2010 #2


    User Avatar

    Staff: Mentor

    Welcome to the PF.

    You will need to show more of your work on #2 and #3 before we can help you. That's how we handle Homework Help here at the PF.

    For #1, you are mostly correct. In general, an "isolation" transformer will be a 1:1 transformer, with the main talk of galvanically insulating the primary from the secondary. However, an "isolating" transformer just means that the primary is insulated from the secondary, so the turns ratio could be whatever is needed for the application.

    Please give us your thoughts on #2 and #3. For #3, what is the voltage ratio equation for a transformer, in terms of the ratio of the number of turns primary/secondary?
  4. Sep 14, 2010 #3
    My thoughts for #2 is that if its used for a bathroom shaver circuit, it needs to be very safe so that no harm can be procured in our face. Not sure if thats quite the answer though because the question says "explain". This is just 2 sentences.

    #3. I can give you a short summary. If its a step down transformer with a 4 to 1 turns ratio, and the input voltage is 480, the output would be 120. So you're dividing with 4. As you do with the primary and secondary coil. I think a step up transformer would be the other way around. 1 to 4 turns = (1x4 = 4.) 120V and 480V. (120Vx4 = 480V.)

    And for #1, if I understood right, the voltage doesn't change due to safety reasons. You, yourself choose a permanent voltage and change it manually.
  5. Sep 14, 2010 #4


    User Avatar

    Staff: Mentor

    You have the turns ratio equation correct for #3, so now put in the turns numbers that they list, and calculate the output voltage answer for #3.
  6. Sep 15, 2010 #5
    Alright, I'll do that in a min. But is my answers for #1 and #2 correct?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook