
Case – I: When n1 = n2 = n, then equivalent focal length of lens is f0.
Case – II: When n1 = n, n2 = n + Δn, then equivalent focal length of lens is f= f0 + Δf0 . Then correct options are:
a) If Δn/n > 0, then Δf0/f0 < 0
b) |Δf0/f0| < |Δn/n|
c) If n = 1.5, Δn = 10-3 and f0 = 20 cm then |Δf0= 0.02 cm
d) If Δn/n < 0, then Δf0/f0 > 0
=
Answer: A and C

If S1S2 = 3mm, OP = 11 mm then
a) If α = 0.36/π degree then destructive interfaces at point P.
b) If α = 0.36/π degree then constructive interfaces at point O.
c) If α = 0 then constructive interfaces at O
d) Fringe width depends an α
Δx = d sin α + d sin θ
= dα + dy/D
(A)
3900 = (2n – 1) λ/2 => n = 7 dest
(B) Δx = 3mm (.36/π) (π/180) = 600 nm
600nm = n600nm
=>n = 1 const
(C) α = 0, Δx = 0
So constructive interference
(D) Fringe width does not depend on alpha;.
Answer: a::b::c
Question 3: A uniform rigid rod of mass m & length l is released from vertical position on rough surface with sufficient friction for lower end not to slip as shown in figure. When rod makes angle 60° with vertical then find correct alternatives
a)
b)
c) N = mg/16
d) aradical = 3g/4


mg – N = mav
N = mg/16
Answer: b::c::d
a)
b) Final pressure is between 9P0 and 10P0
c) |W.D.| = 13 RT0
d) Average Translational kinetic energy
W = [P1V1 – P2V2]/[V-1]
P0V08/5 = P2 (V0/9)8/5
P2 = 9.2 P0
Answer: a::b::c

Make the correct options
a) a2 – a1 = a1 – a3
b) x0 = 4mg/3k
c)
d) Acceleration a1 at x0/4 is 3kx0/42m
2a1 = a2 + a3
a1 – a3 = a2 – a1
When we use m equivalent (for other opitions)
T/g’ = 2(2m)m/(2m+m) = 4m/3
2T/g’ = 8m/3
meq. = 8m2/[m+2m] = 8m/3
(1/2) kx02 = 8mgx0/3
x0 = 16mg/3k
Vx0/2 = Vmax = x0w/2
=
ax0/4 = x0w2/4 = x0/4 * 3k/14m = 3kx0/42m
Answer: a::c::d

a) Net electric field at point A is 3E0
b) Net electric field at point B is Zero
c) Radius of equatorial surface R = (kp0/E0)1/3
d) Radius of equatorial surface R = (√2kp0/E0)1/3

P = (P0/√2) (x + 1)
KP0/r3 = E0
(EA)net = 2KP0/r3 + E0 = 3E0
(EA)net = 0
Answer: b
Which of the following is correct
a) m = 2
b) ΔPa/Pe = 1/2
c) λe = 418 nm
d) Ratio of K.E. of electron in the state n = m to n = 1 is ¼.
Answer: a::d
correct (Assume v <<<< v0 Δl/l ) and collision is elastic)
a) change in speed after collision is 2V
b) change is speed after collision is 2 v0 Δl/l
c) rate of collision is V/l
d) When piston is at l/2 its kinetic energy will be four times.
Change in speed is (2V + V0 – V0) = 2V
Answer: a
Question 9: Calculate the work done if a particle is moved along a path AB−BC−CD−DE−EF−FA, as shown in the figure in presence of a force
dω = αy dx + 2αx dx
E → F, y = 0, dy = 0, W<sub>EF</sub> = 0
F → A, x = 0, dx = 0, W<sub>F → A</sub> = 0
∴ w = α − α − α / 4 − α / 2 = -3α / 4
Given α = −1
⇒ W = + 3/4 J = 0.75 J.
Answer: 0.75 J

e = (V x B) dl = 10-3 v df
i = 10-3(1 – e-1)
i = 0.63 mA
Answer: 0.63 mA



Answer: 1.5

Photons are reflected
MV = 2Nh/λ [mean]
Vmean = αA
A = 1 min
N =
N = 4Mπα/h x 10-12
1024 x 10-12
1 x 10-12
Therefore, X = 1

(P) W1->2 = 1/3 RT0 (Q) Q1->2->3 = 11/6 RT0 (R) U1->2 = RT0/2 (S) W1->2->3 = 1/3 RT0
Which of the following options are correct
a) P, Q, R, S are correct
b) Only P, Q are correct
c) Only R, S are correct
d) Only P, R, S correct
Answer: a

(P) W1->2 = 1/3 RT0 ln 2
(Q) Q1->2->3 = 1/6 RT0 (2 ln (2) + 3 )
(R) U1->2 = 0
(S) W1->2->3 = [RT0/3] ln 2
Which of the following options are correct
a) P, Q are incorrect
b) R, S are incorrect
c) P, Q, S are incorrect
d) None of these
ω1-2 = nRT0 ln 2
Q1-2-3 = Q12 + Q23
= d ω1-2 + dU2-3
= [RT0/3] ln 2 + n (f/2) RT0
= [RT0/3] ln 2 + (1/3) (3/2) RT0
U1-2=0
ω1-2-3 = (1/3) R0T0 ln 2
Answer: d
a) String – 1 (P) T0
b) String – 2 (Q) T0/√2
c) String – 3 (R) T0/2
d) String – 4 (S) T0/16
(T) 3T0/16

Answer:
(A) → P, (B) → R, (C) → T, (D) → S
a) String – 1 (P) 1
b) String – 2 (Q) 1/2
c) String – 3 (R) 1/√2
d) String – 4 (S) 1/√3
(T) 1/16
(U) 3/16
(A) → P, (B) → R, (C) → S, (D) → Q
Video Lessons – Paper 2 Physics




JEE Advanced 2019 Physics Paper 2 Solutions
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