Resistance when 10 bulbs are in parallel,R||=R/10
Resistance when 10 bulbs are in series,Rseries=10R
Voltage acros each bulb in first case is V while in second case is V/10. So first circuit has highest voltage across each bulb. But current in second circuit across each bulb is 10 times that flowing across each blb in first case. So
power dissipated is more in second case per bulb. Thus bulbs brighten more in second case.
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