Please please help me and answer that question.Please answer that question too this is a completion: suppose 15 light bulbs were connected and one...

When all the bulbs are connected or wired in parallel,
burning out of fusing of one of the bulb will not affect any other bulbs. The circuit
for other bulbs will still be closed and they will continue to function normally. In
this case it is easy to spot the defective bulb by just switching on the circuit and
observing all the bulbs to find out which one is not lighting
up.

However, when all the bulbs are connected in series
then burning out of any one bulb will cause the entire circuit to become open. In this
case none of the bulbs will light up in spite of the fact that these are still in
working order. IN this case we will need to examine each of the bulb to find out if it
is burned out. Once we locate the defective bulb we can either replace the bulb with a
good one, or directly connect outgoing wire from previous bulb to the incoming wire of
the next bulb. If there are no other defective bulbs in the circuit all the bulbs will
light up when the circuit is switched on.

The examination
of each bulb to locate the defective bulb may be done in several ways. One way is to
visually examine the filament of the bulb to see if it is burnt out or broken.
Alternatively we can test the continuity of the circuit upto each bulb, we can start
with first bulb in the series after the source of electricity and then continue testing
one additional bulb in each test. When test shows continuity of circuit, all the bulbs
included in the test are OK. When the test shows discontinuity, the last bulb included
in the test is defective.