What is correct: delta E delta t> h' where h'=h/2π
or,delta E delta t> h'/2

generally ~ sign is written in this expression of uncertainty principle...I want to be sure

I think it is the 2nd which is true.
We know (delta x)(delta p)> h'/2
=>[(delta x)/c][(delta p)c]>h'/2
=> (delta t)(delta E)>h'/2

It really depends on how you define the Fourier transform of the wave function.

Some books will use Planck's constant, h. Some will have h-bar (that is, h divided by 2 pi). Some will have h-bar/2.

If I have to choose, I normally go with h-bar/2, since that is the smallest of all the values.

It really depends on how you define the Fourier transform of the wave function

How?
Is it not introducing a confusion?
If required what formula would you use?
For example:The lifetime of the Z boson in weak interaction is provided by
uncertainty principle:∆t=ћ/(Mc²)

but if you put your preferred formula it comes out as:∆t=ћ/(2Mc²)

I am new to these concepts...so please be patient to answer me.

neelakash---

Most modern books and modern (high energy) physicists use hbar. It turns out to be quite convenient to set hbar = c = 1, which I call God's units. It simplifies the formulae and lets you do unit analysis very easily. For example, the energy relation becomes E = m, and the life-time of the Z-boson becomes

\Gamma \sim \frac{1}{M_Z}.

I agree with you.But My problem is not the so-called natural units.What I am woried about is the correct version of Uncertainty principle.My friends told me that both are equivalent.But if that is the case,the we are to admit that there will be 2 values of minimum lifetmes: one is 1/M and another 1/2M.Where the first comes from ∆t=ћ/(Mc²) and the 2nd comes from
∆t=ћ/(2Mc²)
So, contradiction...
Then what is the correct idea?

I think James is correct---it depends on the conventions.

The conventions that most high energy people use include hbar's, because we then set them to one.

may be.But tell me what is correct?
one is 1/M and another 1/2M.Where the first comes from ∆t=ћ/(Mc²) and the 2nd comes from
∆t=ћ/(2Mc²)
So, contradiction...