physics mcq help needed! urgent!

[ifraha18]

oct nv 2007 20..
strain energy is 1/2 *f*l

here the graph is btween l and f..so energy is area above the line...

tht is 1/2*(.4_.2)*25

tht is 2.5J

[ifraha18]

no the resitance decreases as lyt intensity increases

[ifraha18]

nov 2007..25

dsin thetha=n lambda
d sin45=3lambda
d=3lambda/sin45
d=3root2 lambda
the maximum value of sinetheha is 1
so fr highest order...nlamda/d<=sinthetha
                            nlamda/3root2lambda <=1
                            n/3root2<=1
                            n<=3root2
                            n<=4.24


so highest order is 4  

[ifraha18]

nov 2007 37..its a fact given in book

[neno]

q 4,32 of nov 2008?>>>

for 4 i have no clue but 32 i can solve
1 copper wire has resistance 10 length 1000m
resistance =length /area
10=1000/area
area=1000/10
therefore area =100
6 wires so area 600
length the same so therefore 1000/600
which is equal to 1.6

[neno]

Q40 mayjune 2007??

[neno]

Q3,Q21(oct/nov 2006)
Q9(mayjune 2004)

[cashem'up]

Q40 mayjune 2007??

 we know that E = V/d and E= F/q
qE=F , ma=qE , a=qe/m now when we want lowest speed acceleration should be least
so take particle with smallest charge to mass ratio......take E constant here as field will be same......
 

[cashem'up]

Q3,Q21(oct/nov 2006)
Q9(mayjune 2004)

q3 o/no6
we have to use base units
so elecitric field strength = F/Q
so ma/q now m is kg a is m/s² and Q is C
so in this equation we get kgms^-2C^-1

Q9
lets look first at vertical u=0 g=10 s=1.25 t=?
so 1.25=0.5at²
2.5/10=t²
0.25=t²
t=0.5

then applying to horizontal
s=10 u=? t=0.5 a=0
s=ut
u=10/0.5
u=20

[sabrina]

hi guys
my doubt is on oct\nov 2007 Q7. why it cant be A?

[halosh92]

for 4 i have no clue but 32 i can solve
1 copper wire has resistance 10 length 1000m
resistance =length /area
10=1000/area
area=1000/10
therefore area =100
6 wires so area 600
length the same so therefore 1000/600
which is equal to 1.6

Q4:
(2.02+1.98)/2
to get the current value
answer = 2
(1/100)*2=0.02
then because u added in the beginning then u have 2 add uncertainty, this is the rule,
0.02+0.02=0.04
so ans is D

[halosh92]

for 4 i have no clue but 32 i can solve
1 copper wire has resistance 10 length 1000m
resistance =length /area
10=1000/area
area=1000/10
therefore area =100
6 wires so area 600
length the same so therefore 1000/600
which is equal to 1.6

for question 32.....dont u consider the steel core resistance???

[cashem'up]

well yea actually i think  u do it in a slightly different way......THE MAIN THING HERE IS THE WIRES ARE PARALLEL...................
so
1/r= 1/10 + 1/10 + 1/10 + 1/10 + 1/10 + 1/10 + 1/100
so R=1.64
so R=1.6
then

[halosh92]

well yea actually i think  u do it in a slightly different way......THE MAIN THING HERE IS THE WIRES ARE PARALLEL...................
so
1/r= 1/10 + 1/10 + 1/10 + 1/10 + 1/10 + 1/10 + 1/100
so R=1.64
so R=1.6
then

MUCH EASIER
THS

[da_rockstar]

hm....but can you please explain why you took those wires as parralel??
i have a quetion....when we talk about the kinetic energy of a electron in a electric field is there a formula stating that:
  kinetic energy=potential difference across the plates * charge of the electron.

another question which  i wanted to clear was that for example i saw a question that like a specific amount of electrons and protons were moving in oppisite directions in the same wire. they asked about the total charge on it.
so can you explain whether we subtract the charges or do we add them up....

thanks.