IIT JEE , AIEEE Forum - Physics , Optics

iitjee08aspirant

Mirages are observed on some days when
1)Density of air increases with height
2)density of air decreases with height
3)earth acts like a mirror
4)air is dense uniformly
ans given is 1 but i think it shud be 2 plzz correct me

a constant torque acting on a unifrom circular wheel changes its angular momentum from J to 4J in 4 seconds the mag of torque is
1)3/4J
2)4J
3)J
4)12J
ans given is 3 but im gettin 1 am i missing somethin????

an ellipse slides between two straight lines at right angles to each other the locus of its centre is part of
1)auxilliary circle
2)director circle
3)another ellipse
4)parabola

ans given is 3 but i wrote it as 2 wat is wrong???

2 salutes per que assured

rtiit

for 1
i think refractive index is proportional to density
so if density inc
then
critical angle decreases
and TIR can occur easily

iitjee08aspirant

more ans needed

iitjee08aspirant

plzz ppl ans

rtiit

Data are presented on the changes in the room-temperature refractive index and density of a borosilicate crown glass produced by different heat-treatments. Measurements on a large number of samples with widely varying thermal history show that the refractive index is a single-valued function of the density. The increase in refractive index for a given density change is smaller than that calculated by the Lorentz-Lorenz theory; the apparent contribution of the induced polarization to the local electric field is very small. This may be due to a reduction in the ionic polarizabilities that accompany the density increase; alternatively, the Lorentz-Lorenz form of the theory may not be valid in solid materials such as glass. Data of other investigators are shown to agree with the data reported here.

source net

blackjack

for 3-
let 2a and 2b be the length of the major and minor axes. If the ellipse slides betwn two perpendicular lines, the point of intersection P of these lines being the point of intersection of perpendicular tangents lies on the Director circle of the ellipse. This means that the centre of the ellips is always at a const distance rt(a^2+b^2) frm P. Hence locus of center is a director circle.
thus, ans is B

rtiit

hey but ans is 3

iitjee08aspirant

arre yaar yukti hai it can be wrong

iitjee08aspirant

yaar plzz ans its so ezee que just wanna confirm them

spideyunlimited

Mirages are observed on some days when
1)Density of air increases with height
2)density of air decreases with height
3)earth acts like a mirror
4)air is dense uniformly

for a mirage to occur... a light ray must go from denser to rarer medium and undergo Total internal reflection.. and here the air near the ground. which is hot, is rarer..
and density increases upwards.

so option 1 is correct

ashish_banga

answer to first is 1
density of air increases with height
a ray of light coming from a tree towards ground bends away from the normal( denser to rarer)
so TIR occurs
it appears to be coming reflected by water

iitjee08aspirant

wat abt other two guys???

dream

see
for 2: i believe the answer as 3J/4

and for 3: i think the answer shud be ellipse
of u say that it is director circle, then its radius is greater than that of any axes of given ellipse...................which is not possible as the ellipse shud be in between given two axes
see i have not solved it, but i have just used logic out there

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