Question

holiday lights are often connected in series and use special lamps that short out when the potential difference across a lamp increases to the line voltage. generate an explanation why and explain why these light sets might blow their fuses after many bulb

Answer 1

Explanation:

If there isn't the shorting mechanism, the whole set will be blown if anyhow one lamp burns out. Since having blown out several lamps and then shorted, the overall resistance of the remaining operating lamps will be decreased  resulting in an increased working current that is adequate to blast the fuse.