Alaser pulse with wavelength 550 nm contains 4.40 mj of energy. how many photons are in the laser pulse?

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Solution:- First of we calculate the energy of the laser pulse for it's given wavelength which actually the energy in joule per photon. After this the given energy value is divided by the calculated energy to find out the number of photons.

The calculations are done as:

For energy calculations the equation used is:

where, E is energy, h is planck's constant and is the wavelength.

The values of the constants are as follows:

wavelength is given as 550 nm. We need to convert it to m.

Let's plug in the values in the equation to calculate E:

This is the energy for one photon. The given energy value is 4.40 mJ that is .

let's divide this value by the calculated value to get the number of photons as:

=

So, there would be photons in the laser pulse.

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)