Hello student yes PhD is very useful and rather than useful it's very valuable and informative if you do PhD then you must know what's your value after PhD. To become a lecturer in any government college the minimum eligibility is PhD. PhD is not just a course its an end of academic course this is why it's very valuable. And after B.tech degree usually students prefer for a doctorate degree because after doctorate degree the placement are is very high and good.
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Good luck
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