.

[clıppy]

Guessing he got it from reddit, before it ended up on that page (I'd find the link, but ceebs)

EDIT: There we go: http://www.reddit.com/r/funny/comments/1n6t00/my_professor_said_i_could_only_use_one_notecard/

Doing the Repost God's work.

[PB]

Hey Social Rhubarb,
I still don't quite understand how the Back EMF concept works? I am just thinking - if the secondary coil circuit has no load, the primary current will just keep circulating wouldn't it? What is this back EMF and where on earth does it come from??
Doesn't the transformer then just work like a normal solenoid with an iron core? (lel, i am part of that majority that don't know my shit..)

[lzxnl]

Hey Social Rhubarb,
I still don't quite understand how the Back EMF concept works? I am just thinking - if the secondary coil circuit has no load, the primary current will just keep circulating wouldn't it? What is this back EMF and where on earth does it come from??
Doesn't the transformer then just work like a normal solenoid with an iron core? (lel, i am part of that majority that don't know my shit..)

I'm not SocialRhubarb

If the secondary coil circuit has no load, the primary coil can still induce an emf and current to oppose the changing magnetic flux through it. If your primary coil had a constant current, then yes it would keep going, but your transformer wouldn't work. Note that as your secondary coil circuit is empty, it's effectively not there as a current can't be induced.

If your secondary coil does have a load, a current is induced in the secondary coil in the same direction as the back emf in the primary coil. This induced current itself also generates a changing magnetic field which induces another current in the primary to oppose the induced current. This second induced current in the primary is of opposite sign to the induced current in the secondary, which is of the opposite sign to the original current. Therefore the second induced current in the primary coil SUPPORTS the original current and emf. Thus having a load in the secondary coil makes a world of difference.

[Stevensmay]

So this year we are allowed to bring in 2 double sides a4 sheets of paper?
It's the same size as A3 I personally feel splitting unit 3 to one sheet and unit 4 to the other is more logical

But they must be bound together with tape so you might as well bring in an A3 sheet.

[SocialRhubarb]

Yep, basically what nliu1995 said.

It's interesting though that solenoids by themselves actually experience this too, and solenoids without a load do not, as some would predict, have huge currents passing through them when a voltage is applied, but instead reach a modest current, with the scale of the current depending on the nature of your solenoid, and how close it is to ideal.

[PB]

Lol, ok so to reiterate. The AC current in the primary coil creates a changing magnetic field which is basically counterproductive for itself as the very same primary coil will try to offset this changing magnetic flux with a "Back EMF" - so no current.
However, with a load in the secondary coil, the AC current can flow in the secondary coil, which basically negates that Back EMF, so its all good and the current keeps circulating?

[lzxnl]

Not really negate...but you have the basic idea.

I'd prefer "an AC current" rather than "the AC current" as we're not speaking about only one possible current.
But yeah, it's like we've induced two current from the initial AC currents and the second induced current partially offsets the back EMF.

[#1procrastinator]

wtf, double-sided A3?!

[PB]

Righto, although I think it should be just an AC (cus AC stands for alternating current) - AC current would mean alternating current current, a bit redundant

[Twanny666]

Is a laminated cheat sheet allowed?

[Damoz.G]

Is a laminated cheat sheet allowed?

Even though its not stated whether or not you are allowed, I'd say probably not. I wouldn't take the risk.

May be ask your VCE Coordinator or Physics teacher?