i) A 100 W and 60 W bulb are joined in series and connected to the mains. Which bulb will glow brighter? Why? ii) A 100 W and a 60 W bulb ar

Question

i) A 100 W and 60 W bulb are joined in series and connected to the mains. Which bulb will glow brighter? Why? ii) A 100 W and a 60 W bulb are joined in parallel to the mains. Which bulb will glow brighter? Why?

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Thành Đạt 1 month 2021-08-11T09:36:01+00:00 1 Answers 0 views 0

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    2021-08-11T09:37:33+00:00

    Answer:

    i) 60 W

    ii) 100 W

    Explanation:

    In each case, the bulb that dissipates the most power is the bulb that glows brighter.  Power is voltage times current (P = VI).  Using Ohm’s law, we can rewrite this as P = I²R or P = V²/R.

    Bulbs are rated at a certain power for a certain voltage.  P = V²/R, so the bulb with the lower resistance will have the higher power rating.  Therefore, the 100 W bulb has a lower resistance than the 60 W bulb.

    i) They are in series, so they have the same current.  P = I²R, so the bulb with the higher resistance will glow brighter.  That’s the 60 W bulb.

    ii) They are in parallel, so they have the same voltage.  P = V²/R, so the bulb with the lower resistance will glow brighter.  That’s the 100 W bulb.

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