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Physics Problem

  • 27-10-2013 3:19pm
    #1
    Shade Of Wolf
    Registered Users, Registered Users 2 Posts: 2 ✭


    Hi all!! We have to sort out this Physics Problem in college, and while I've done a lot of work on it, I only have bits and pieces. To be honest, it's driving me a bit crazy. Any help would be greatly appreciated!:


    The Shoddy Wiring Company





    You are an electrician called intoinvestigate the wiring a house which has been done by an apprentice who is onwork placement with the Shoddy Wiring Company. At the moment there are the following items connected to the housewiring: a 100 W toaster, a 750 W microwave, a 75W light bulb, a 60W light bulb,a 800 W washing machine, and a stereo with two 50 W speakers.

    You do a number of tests and findthe following.



    · You switch on only the 75Wlight bulb and find it works properly.

    · You switch on the 75W and60W light bulbs and find that they emit together about as much light as a 33 Wbulb on its own.

    · You switch on the toasterand the 75W bulb and find that they work properly.

    · The stereo works properlywhen the 75 W bulb is on but not if the 60 W bulb is on.

    · You switch on the washingmachine and the 60W bulb and find that they work properly.

    · You switch on the toaster, microwave,and washing machine together and find that none works properly.





    Determine and sketch thecircuit which the apprentice has set up.

    Sketch the circuit whichshould have been set up.

    The main supply is 230 V rms.

    · Determine the resistance ofthe filaments in the light bulbs.

    · If only the 75 W bulb isswitch on how much current flows through it.

    · If the toaster, the stereoand both light bulbs are switched on, what is the current flowing through andthe voltage drop across each.


Comments

  • #2
    whizbang
    Registered Users, Registered Users 2 Posts: 1,974 ✭✭✭whizbang


    It seems the 60W bulb is common to a lot of these, so maybe its in series, with a switch across it?

    you should post this in the Electrical forum, the lads there will suss it


  • #3
    clartharlear
    Registered Users, Registered Users 2 Posts: 489 ✭✭clartharlear


    That's a fun problem!

    If things work properly, then they're getting full voltage from the source so they must be on parallel branches. If they don't work properly when on at the same time, they must be in series with each other.
    e.g. the two bulbs must be in series with each other, but the stereo must be connected in parallel across the 75 W and not to the 60 W.

    Are the following questions about the shoddy circuit or the one that *should* have been set up?

    Use P = V^2/R for the resistance of the light bulbs and P = IV for the current.


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