# Help energy physics please

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Could someone explain 4dii in simple terms please;

http://pmt.physicsandmathstutor.com/...%20Imaging.pdf

MS: http://pmt.physicsandmathstutor.com/...aging%20MS.pdf

In the previous part we worked out the power to be 12,000W.

So I thought that since we're giving a time... P*t= E of electrons so I did 12,000 * (7.5*10^13) and equalled this to 1/2mv^2 but this was wrong - why does the markscheme divide the P/t ??

http://pmt.physicsandmathstutor.com/...%20Imaging.pdf

MS: http://pmt.physicsandmathstutor.com/...aging%20MS.pdf

In the previous part we worked out the power to be 12,000W.

So I thought that since we're giving a time... P*t= E of electrons so I did 12,000 * (7.5*10^13) and equalled this to 1/2mv^2 but this was wrong - why does the markscheme divide the P/t ??

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(Original post by

Could someone explain 4dii in simple terms please;

**MrToodles4**)Could someone explain 4dii in simple terms please;

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(Original post by

We did this one two weeks ago... https://www.thestudentroom.co.uk/sho...8#post76890288

**Pangol**)We did this one two weeks ago... https://www.thestudentroom.co.uk/sho...8#post76890288

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**Pangol**)

We did this one two weeks ago... https://www.thestudentroom.co.uk/sho...8#post76890288

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?

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(Original post by

I feel like this is a similar question: http://pmt.physicsandmathstutor.com/...g%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?

**MrToodles4**)I feel like this is a similar question: http://pmt.physicsandmathstutor.com/...g%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?

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.

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(Original post by

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.

**BobbJo**)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.

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**BobbJo**)

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.

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?

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(Original post by

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)

**MrToodles4**)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)

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.

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(Original post by

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.

**BobbJo**)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.

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