Hey dudes ####### (1 Viewer)

[CrashOveride]

hey just something quick

in last years question with the flexible wire loop on the frictionless table, current running thru it.....

why wud it even change shape?? theres no magnetic field so what force is being exerted upon it?

thanks

 

[jumb]

Which question?

nm 10?

Edit: oh crap what the fuck does that mean?

 

[gordo]

there is a curren running through it, so it sets up its onw magnetic field, taht influences other bits of the wire which are parallell to it at those 4 points, since the currents are travelling in opposite directions they repell (opposite currents repel) so the wire widens to a loop

i doubt they willl ask it again this yr though

 

[jumb]

So its like, the circle?

 

[gordo]

indeed it is

 

[gordo]

at all directly opposite points on the circle the currents are flowing in opposite directions thus repelling each other

therefore the circle

 

[CrashOveride]

also hmm for the one with the orbits, X has radius r Y has radius 4r
i used keplers law

r^3/(T_1)^2 = (4r)^3/(T_2)^2
where T_1 is the period of orbit for X, T2 period orbit for Y

and i get that Ty=2Tx, so that in one period of X we have half period of Y? :S

 

[jumb]

While we're on that paper, how do you do 15?

 

[jumb]

also hmm for the one with the orbits, X has radius r Y has radius 4r
i used keplers law

r^3/(T_1)^2 = (4r)^3/(T_2)^2
where T_1 is the period of orbit for X, T2 period orbit for Y

and i get that Ty=2Tx, so that in one period of X we have half period of Y? :S

Yeah, that maeks sense, its b.

 

[CrashOveride]

they say its 1/8 not 1/2 revolutions that Y makes in the time X makes one complete rev.

 

[jumb]

yeah, you didnt cube the 4

(I worked it out) so its a

 

[CrashOveride]

feck @@$@$#$$
thanks dude

also, whats the deal with the glass in hert'z experiment? did he actualy use it?
how does it make the sparks lower?

 

[CrashOveride]

the hertz thing was q14 last year. do you need explanation for 15?

 

[CrashOveride]

for 15, the magnetic force and electric force balance out. So equte F=qE with F=qvB
you get that B=E/v , which u sub in values and u get 0.8T

then u can see thats the magnetic force is making it go up, thus electric force must make it go down so that its undeflected, this meants that the bottom one is -ve and so the top is +ve

 

[CrashOveride]

Does anyone know why glass being placed in between the receiver and tranismitter in Herz's experimemt means that the spark induced will be shorter???

 

[smallcattle]

radiowaves can be reflected, therefore by placing a metal sheet in between means less signal received by the receiver i guess