4@Sourav : I got the same ans as urs for 2nd But ans given is different :(
1) STATEMENT 1 : A charged particle is accelerated by a potential difference V .
The electron enters perpendicular into a uniform magnetic field.The magnitude of angular
momentum of the electron about centre of trajectory followed by it is L.Now if V is doubled , L is
also doubled
STATEMENT 2 : If pot diff V is doubled , KE is doubled & so L is doubled
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18 Answers
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1@soumik L= \frac{2Vm_{electron}}{B}
L=\frac{2KE.m_{electron}}{qB}
now tell me how wen V is doubled L becomes root2 times
i mean jus seeing the formula abov
and i think i hav found out them correctly[3]
11@ joker.....think of what happens in photo-electric effect!
Vq=1/2mv^2....If V is doubled, v becomes root 2 times, so mvr becomes root 2 times....
1in ur formula only in L =2mV/Bq
KE/q=V
replace V by KE/q
so L is straightaway related to KE
1how can u say it has no relation...
i may be wrong.......but then wat abt this relation L=2Km/Bq
1As KE doubles,velocity increases √2 times.
At the same time,r=mv/qB also increases √2 times.
Now, L=mvr,
here as both v and r increase √2 times, L increases √2*√2=2 times.
So on the whole,as Potential diff V is doubled,L also doubles.
i too wrote A.
cant see why it has been given as B.
1if u try to find L it is
L= \frac{2Vm_{electron}}{B}
L=\frac{2KE.m_{electron}}{qB}
KE=qV
hence we can clearly see that wen V is doubled L is doubled
and wen ke is doubled L is doubled
and i think ans shud be A ...perhas fiitjee ppl my hav gone mad [3]
4@Soumik : 1st qs is inviting different views I request someone to confidently explain
what is corrrect
1k.E=eV velocity will change
r=mv/qB will change
substitute
L=mvr
i marked (a) but answer given is(b)
11How does L double if K.E is doubled?
K.E doubled means velocity increases by \sqrt{2} times.....not 2 times!
3as two wires are of same material on both sides of null point there wil be equal change
1even i had marked A for question 1
for question 2,statement 1 true but statement 2 is false.........i dont remember d answer...is dis d answer given?
42) STATEMENT 1 : In meter bridge, if its wire is replaced by another wire having same length made of same material but having twice the cross sectional area, the null point does not shift.
STATEMENT 2 : If its wire is replaced by another wire of same material, having same cross sectional area but of twice the length, the null point does not shift.
4@ :
Its also given that V doubles in the 2nd statement So that can also suffice as a reason I guess