Do the same pickup really sounds different if placed on bridge or neck i heard it does so why or how??

Position does matter however bridge and neck pickups have different outputs. This is from the Seymour Duncan FAQ:

What's the difference between neck, middle and bridge position pickups?
The difference in bridge vs. neck/middle pickups is their output. There is naturally less volume generated from the bridge pickup due to less string movement the closer the pickup is to the bridge. Bridge pickups are usually wound hotter than neck/middle pickups to compensate for the reduced string movement. This produces an even output between all the pickups.

more at
http://www.seymourduncan.com/websit...ridgemiddleneck

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Pickups sound warmer in neck position , just as picking the strings closer to the neck sound warmer than going closer to the bridge.

To overcome the volume difference problem , or making the volume even while you change pickups as you play , some people use different pickups , others use the same pickup and make the bridge pickup higher (closer to the strings) than the neck pickup.