1. Xtra Edge February 2012 - Career Point

Direction of incident rays is inclined at angle θ with
normal to the plane of ring. Therefore, power
incident on the ring, p = (2πxdx)I cos θ
P cosθx
dx
or p =
2
2r
Since, incident power is in the form of light rays
which are incident at angle θ with normal to the
plate, therefore, net rate of incidence of momentum
on the ring considered
2
P cos θ P cos θ x dx
= =
c
2
2r
c
Since, 70% of the rays are reflected and 30% are
absorbed by the plate, therefore, rate of change of
momentum from the ring considered
1
= [(0.7 p cos θ) × 2 + (0.3 p cos θ)]
c
But it is equal to force dF on the ring.
Pa x dx
∴ dF = 0.85
2 2 2
c(
a + x )
or Total force on the plate,
2 x=
R
0.
85Pa
x dx
F = ∫ 2 2
c ( a + x )
XtraEdge for IIT-JEE 20 FEBRUARY 2012
=
0.
85Pa
2c
2
2
x=
0
⎡ 1
⎢ –
2
⎢⎣
a ( a
2
2
2
1 ⎤
2 ⎥
+ R ) ⎥⎦
0.
85PR
=
= 1 × 10
2 2
2(
a + R ) c
–10 N Ans.
NUCLEAR REACTOR TYPES – ARE THEY REALLY SAFE?
The nuclear power industry along with the reactor technology has been constantly developing for more than five
decades now. Nuclear reactors can be classified based on their nuclear reaction, the moderator material used,
generation of the reactor, fuel phase, fuel type, coolant used, etc. The fission nuclear reactors are mostly dealt with
because the fusion reactors are still in the developing stages and the fission reactors are already being used for the past
six decades.
• Based on nuclear reaction
This type refers to the thermal (slow) reactors and the fast reactors based on the speed of neutrons. Thermal
reactors are the most affordable and common as they use the natural and raw uranium; and the neutrons are
decelerated from their natural speed when emitted from the broken atomic nuclei, and uses a moderating material
in the process. The Fast reactors are very expensive that require more enriched fuel.
• Based on moderator material
Thermal reactors (because of the presence of the moderating material), and Graphite, Normal water and Heavy
water are also used as moderators. The moderating materials in the Graphite and the Heavy water reactors
thermalize the neutrons and keep the natural uranium intact without any enrichment.
• Based on generation
Generation I reactors were the first prototype reactors, Generation II used standard designs till 50s, Generation III
were more modern, lightweighted, more efficient and were used till late 90s, the latest i.e. Generation IV reactors
targeting on economical and minimal waste, are still in the research and development stage which may officially
work until late 2020s.
• Based on fuel phase and fuel type
It is Solid, Liquid or Gas reactor where Solid is most typical. The fuel type reactors also come with fuel phaseuranium
or thorium, which are available in abundant quantities on the land.