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Test Index
JEE Advanced 2019 Paper 2
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Section:
Physics
Share question:
© examsnet.com
Question : 1 of 54
Marks:
+1
,
-0
A free hydrogen atom after absorbing a photon of wavelength
λ
a
\lambda_a
λ
a
gets excited from the state n = 1 to the state n = 4. Immediately after that the electron jumps to n=m state by emitting a photon of wavelength
λ
e
\lambda_e
λ
e
.Let the change in momentum of atom due to the absorption and the emission are
Δ
p
a
\Delta p_a
Δ
p
a
and
Δ
p
e
\Delta p_e
Δ
p
e
, respectively. If
λ
a
λ
e
=
1
5
\frac{\lambda_a}{\lambda_e}=\frac{1}{5}
λ
e
λ
a
=
5
1
, which of the option (s) is /are correct ?
[Use
h
c
=
1242
eV
nm
;
1
nm
1
0
−
9
hc=1242\,\text{eV}\,\text{nm};1\,\text{nm}\,10^{-9}
h
c
=
1242
eV
nm
;
1
nm
1
0
−
9
] m, h and c are Planck’s constant and speed of light, respectively]
[JEE Adv 2019 P2]
Δ
p
a
Δ
p
e
=
1
2
\frac{\Delta p_a}{\Delta p_e}=\frac{1}{2}
Δ
p
e
Δ
p
a
=
2
1
The ratio of kinetic energy of the electron in the state n = m to the state n = 1 is
1
4
\frac{1}{4}
4
1
m
=
2
m=2
m
=
2
λ
e
=
418
\lambda_e=418
λ
e
=
418
nm
Validate
Solution:
1
λ
a
=
R
(
1
−
1
16
)
\;\; \frac{1}{\lambda_a}=R\left(1-\;\; \frac{1}{16}\right)
λ
a
1
=
R
(
1
−
16
1
)
1
λ
e
=
R
(
1
m
2
−
1
4
2
)
\;\; \frac{1}{\lambda_e}=R\left(\;\; \frac{1}{m^2}-\;\; \frac{1}{4^2}\right)
λ
e
1
=
R
(
m
2
1
−
4
2
1
)
λ
a
λ
e
=
(
1
m
2
−
1
4
2
)
15
16
=
1
5
\;\; \frac{\lambda_a}{\lambda_e} = \;\; \frac{ \left(\;\; \frac{1}{m^2} - \;\; \frac{1}{4^2} \right) }{ \;\; \frac{15}{16} } = \frac{1}{5}
λ
e
λ
a
=
16
15
(
m
2
1
−
4
2
1
)
=
5
1
1
m
2
=
1
4
2
+
3
16
\;\; \frac{1}{m^2} = \;\; \frac{1}{4^2} + \;\; \frac{3}{16}
m
2
1
=
4
2
1
+
16
3
1
m
2
=
1
4
⇒
m
=
2
\;\; \frac{1}{m^2} = \;\; \frac{1}{4} \Rightarrow m=2
m
2
1
=
4
1
⇒
m
=
2
⇒Kinetic energy
α
1
n
2
\alpha\;\; \frac{1}{n^2}
α
n
2
1
K
m
K
1
=
1
2
2
×
1
=
1
4
\;\; \frac{K_m}{K_1} = \;\; \frac{1}{2^2} \times 1 = \;\; \frac{1}{4}
K
1
K
m
=
2
2
1
×
1
=
4
1
13.6
(
1
4
−
1
16
)
=
1242
λ
e
13.6\left(\;\; \frac{1}{4} - \;\; \frac{1}{16}\right) = \;\; \frac{1242}{\lambda_e}
13.6
(
4
1
−
16
1
)
=
λ
e
1242
13.6
(
3
16
)
=
1242
λ
e
13.6\left(\;\; \frac{3}{16}\right) = \;\; \frac{1242}{\lambda_e}
13.6
(
16
3
)
=
λ
e
1242
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