EMF = Blv

[matteh]

is this on the course? in the TSFX 2008 they use this, where a plane is traveling through a constant magnetic field at a constant speed, i would have thought a current is only induced for a changing flux?

[cara.mel]

what's the exact question?

if the area of the loop is changing that will induce a current, that could be it.

edit: TSFX are good at including stuff not on the course. I don't remember the VCAA study design any more but I'm leaning towards no its not on it but I'm not confident in my answer

[matteh]

"An aeroplane with a wing span of 25 meters is flying over the south magnetic pole located within the Antartic, at 540 km hr^-1. The magnetic field with this region is vertically orientated and the magnetic field strength is 6.0 x 10^-5 T"

--- "What is the magnitude of the emf induced across the wing tips?"

there's a diagram with a plane and field lines underneath it pointing up towards it, here are the solutions by tsfx..

"velocity = 540 = ms−
emf = Bl v = 6.0 × 10−5 × 25 ×150 = 0.23V (0.225V )"

[ReVeL]

Wtf. Never seen that before.

[champorado]

Oo, there was a question like that on the 2006 paper.

Too long to write, but basically a wire that forms a square with side length 2cm. It travels through a magnetic field at 4cm/s. Find the maximum induced voltage in the loop if the field strength is 3.7 x 10^-3.

You could either use Blv, which is just a simple .02 x .04 x 3.7 x 10^-3, or you could use n(delta)flux / (delta)time. It's a bit more work, but you get the same answer.

Anyway, when the plane enters the pole's field, the flux does change. Most of the questions on induced voltage I've seen use the latter formula, though. Just write it on your formula sheet, it won't take up that much space.

[onlyfknhuman]

Yes blv is in the course,

i find tsfx really insightful lol, and that question is a simple substition of numbers.

Hopefully we dont get something circuit and transformer based, like that tram question in 04 was it, fckn hated that.

[matteh]

ah yea i remember that question, didn't use Blv though. This sort of thing relates to an instantaneous sort of induced emf right? because it doesn't specify that the plane exits the field so it wouldn't be constantly producing an emf correct?

[onlyfknhuman]

Too what i can see, yea its instantaneous.

[mark_alec]

I'll try to offer some explanations for the emf induced across a conductor of length , travelling with velocity through a magnetic field . This is not required knowledge.

The conductor has charges in it, and by travelling through the magnetic field, a force will cause them to travel to one side of the wire. This charge separation in turn, creates an electric field which has a force on the charges . This will happen until an equilibrium is reached when . There is now an electric field across the conductor, and since , where is the distance, it is clear that

Alternatively, using a concept of flux.

[onlyfknhuman]

what the ... i feel stupid

[matteh]

Ah yeah, how would you determine which end the charge builds up on? I don't see how you can do this with RH grip rule?

[onlyfknhuman]

current = flow of positive charge.

hence direction of current is the direction were positive charge are.

And obviously the opposite is were the negative charge are.

[matteh]

yeah but how do you determine that from just the direction of the field?

[mark_alec]

Ah yeah, how would you determine which end the charge builds up on? I don't see how you can do this with RH grip rule?

Right hand slap rule. The force on a positive charge moving with a velocity in the direction of your thumb, through a magnetic field in the direction of your fingers (when out straight), will be perpendicular to your palm (in the direction you would 'slap'.)

[onlyfknhuman]

what?

Right hand slap rule => palm = force / fingers = field / thumb = current . charge flows within a conductor . so no idea what you dont know.