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# Two quick AS-Level questions on electromotive force/potential difference watch

1. Hey,
I'd be grateful if anybody could help me with either of these questions:

1. When an electron is accelerated across a potential difference of about 15V it has enough energy to ionise a nitrogen atom, that is, to remove an electron from an atom by collision with it. How many attojoules, symbol aJ, is this? 1.0aJ = 1.0 x 10-18 J

2. When you collect cells in series you add the e.m.f.s together to find the total e.m.f. of the battery. Prove this statement by answering the following question for three cells of e.m.f. E1, E2, and E3.
The total e.m.f. E is defined as the energy provided by the battery divided by the charge passing. Hence, show that E=E1 + E2 + E3.

Thanks
2. To answer 1 you need to know the binding energy of an electron in Nitrogen. Assuming its a core electron, this will be 410eV (See here: http://www.webelements.com/nitrogen/...roperties.html)

To convert from eV (electronvolts) to aJ, use

One thing though: if the electron has been accellerated over 15V, its gained 15eV of energy. The question doesn't make complete sense to me though as this isn't enough to ionise nitrogen; barely enough to ionise hydrogen, which has an ionisation energy of 13.6eV.

Not sure about Q2, something about a series circuit having the same current at all points perhaps?
3. To answer 1 you need to know the binding energy of an electron in Nitrogen. Assuming its a core electron, this will be 410eV (See here: http://www.webelements.com/nitrogen/...roperties.html)

To convert from eV (electronvolts) to aJ, use

1eV = 1.6\times10^{-19}J = 0.16aJ

One thing though: if the electron has been accellerated over 15V, its gained 15eV of energy. The question doesn't make complete sense to me though as this isn't enough to ionise nitrogen; barely enough to ionise hydrogen, which has an ionisation energy of 13.6eV.
The answer in the back of the book says 2.2aJ if that helps?
4. The answer in the back of the book says 2.2aJ if that helps?
Still confused as I would make the answer either if we're talking about ionising a core (1s) electron or

if its a 2s electron. But 15eV in attojoules is 2.4aJ, so maybe thats what the book means? It does say 'about 15eV' in the question...

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