# HSC Physics Marathon 2016 (1 Viewer)

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#### Nailgun

##### Cole World
Quick question:

There's a question that needs to use the Earth's orbital period.

I used the orbital period of 23h56mins (converted to seconds), however the sample answer used 24h.

Would I lose a mark? Because Earth's orbital period is actually 23h56mins?
You over estimate the HSC lol.

#### Jeff_

##### Member
You over estimate the HSC lol.
Well I think the textbooks say it's 23h56m.

I think the better way of asking the question was if it's better to use the exact or 24h.

Some schools can be very pedantic about stuff like these and of the marking criteria says no then there's no point arguing haha!

#### loje

##### New Member

Hi, can someone explain why this graph shows that it could be both AC and DC? Maybe a trick in the wording of the question (as I thought DC only produces positive emf?)

This is from the Independent 2013 btw.

Thanks

#### Crokes98

##### New Member
You're right about DC only producing positive EMF, I have no idea...
What does the marking criteria say?

#### Fizzy_Cyst

##### Well-Known Member

Hi, can someone explain why this graph shows that it could be both AC and DC? Maybe a trick in the wording of the question (as I thought DC only produces positive emf?)

This is from the Independent 2013 btw.

Thanks
Both AC and DC generators produce AC in the coil! Think about it, 2 identical coils, rotating at identical speeds in an identical magnetic field -- should produce identical EMF (AND THEY DO!)

AC gets changed into DC via the split ring commutator as it moves from the coil into the external circuit

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#### UnbiasedProductivity

##### The lurker.

Hi, can someone explain why this graph shows that it could be both AC and DC? Maybe a trick in the wording of the question (as I thought DC only produces positive emf?)

This is from the Independent 2013 btw.

Thanks
Because it's a generator. All generators produce AC. DC generators use split ring commutators, to change it into DC. I think. I maybe completely wrong.

#### UnbiasedProductivity

##### The lurker.
Oh lol. I was right. Now I don't have to worry about my ego being destroyed.

#### dan964

##### MOD
Moderator
Thread will be closed. The 2017 marathon is now sticked for easy access.

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