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    A 6.0V torch battery consists of four 1.5V cells connected in series. It is connected to a bulb rated at 6.0V, 0.5A

    a) calculate the resistance and the power generated in the bulb when it is in normal operation

    b) After a time, each cell develops an internal resistance of 0.15Ω. Show that the p.d. across the bulb falls to about 5.7V, assuming that the resistance remains the same.

    c) To what extent is the assumption in part b reasonable?

    I'm having difficulty with part c of the question, the rest I think I got the right answers to.





    Thanks in advance
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    (Original post by KK.Violinist)

    c) To what extent is the assumption in part b reasonable?

    I'm having difficulty with part c of the question, the rest I think I got the right answers to.
    This is concerned with tacit assumptions made vs the practical limits of reality.

    1) the manufacturer specification for the batteries and lamp, state 'nominal' values which vary in practice. The question assumption is that all the batteries and lamps are identical - they are not. This means the internal resistance and actual terminal p.d. can and will differ between batteries, as will the resistance and hence current drawn by the lamp.

    2) the lamp element has a thermal coefficient and its' resistance will therefore change dependent on the supply voltage.

    Measured results and actual performance will differ from nominal calculations.

    3) the technology of the batteries and torch bulb can be different with implications for both above. e.g. battery composition, incandescent vs semiconductor lamp etc.
 
 
 
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