Help energy physics please

Could someone explain 4dii in simple terms please;

We did this one two weeks ago... https://www.thestudentroom.co.uk/showthread.php?t=5280398&p=76890288#post76890288

We did this one two weeks ago... https://www.thestudentroom.co.uk/showthread.php?t=5280398&p=76890288#post76890288

I feel like this is a similar question: http://pmt.physicsandmathstutor.com/download/Physics/A-level/Topic-Qs/OCR-A/6-Particles-and-Medical-Physics/6.5-Medical-Imaging/Set-M/Medical%20Imaging%201%20QP.pdf

for 1bi they divide the current by the charge of an electron? Which is a bit confusing at Q=IT and you're given the current so in 1 second I guess the charge is 4.8*10^-3 ? and then they divide the total charge by the charge of a single electron to work out number of electrons?

Q=ne

and Q=It

So, ne=It.

You need the number of electrons per unit time = n/t.

Rearranging we find that n/t=I/e.

Q=ne

and Q=It

So, ne=It.

You need the number of electrons per unit time = n/t.

Rearranging we find that n/t=I/e.

Then I just don't fully understand why they multiply by 0.99% - 0.99 or 99% (not both!) - i understand that this is the amount of KE that gets converted into thermal energy (per second) - so does this automatically mean the power is also 0.99% converted? yes

My initial thought was to do eV to work out KE and find 99% of this but this was wrong - is it because we want power? But eV will only give you the KE of one electron. If you multiply this by n/t, you will get the total KE per second (because (neV)/t = IV=P)

99% of the KE gets converted into heat energy.

Since power is the amount of energy transferred per unit time, 99% of the power input (kinetic energy per second) gets converted into heat energy per second.

So 0.99P=mc(θ/t)

There are different ways to find P. The easiest is using P=IV. The other is finding the KE of one electron as you did (eV), then multiply by the number of electrons (n/t) you found earlier. You'll get P=neV/t = (ne/t)V=IV.