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NEET Physics Solved Question Paper 2009

Multiple Choice Questions

41.

de Broglie wavelength λ associated with neutrons is related with absolute temperature T as

λ ∝ T
λ ∝ $\frac{1}{T}$
λ ∝ $\frac{1}{\sqrt{T}}$
λ ∝ T²

42.
A nucleus of mass number 220 decays by $α$ decay. The energy released in the reaction is 5 MeV. The kinetic energy of an $α$ -particle is

$\frac{1}{54}$ MeV

$\frac{27}{11}$ MeV

$\frac{54}{11}$ MeV

$\frac{55}{54}$ MeV

$\frac{54}{11}$ MeV

Let the reaction can be represented as

${}_{Z}^{220}X \to {}_{Z - 2}^{216} Y + {}_{2}^{4} He$

since energy released in the reaction is 5 MeV

⇒ $\frac{1}{2} m_{γ} ν_{γ}^{2} + \frac{1}{2} m_{α} ν_{α}^{2}$ = 52 MeV

⇒ $\frac{1}{2} (216) ν_{γ}^{2} + \frac{1}{2} (4) {(ν_{α})}^{2}$ = 5 MeV ....(i)

Also using conservation of linear momentum

m_γ ν_γ = $-$ m_αν_α

⇒ ν_γ = $\frac{- m_{α}}{m_{γ}} ν_{α}$

ν_γ = $\frac{- 4}{216}$ ν_α

ν_γ = $\frac{- 1}{54}$ ν_α

Putting in equ (i)

$\frac{1}{2} (216) {(\frac{ν_{α}}{54})}^{2} + \frac{1}{2} (4) {(ν_{α})}^{2}$ = 5 MeV

$\frac{1}{2} (216) {(\frac{ν_{α}}{54})}^{2} + K . E ._{α}$ = 5 MeV

⇒ $\frac{1}{2} \times 4 (\frac{ν_{α}^{2}}{54}) + K . E ._{α}$ = 5 MeV

K.E._α = $\frac{5 \times 54}{55}$

K.E._α = $\frac{54}{11}$ MeV

43.

The wavelengths of K_α X- rays for lead isotopes Pb²⁰⁸ , Pb²⁰⁶ and Pb²⁰⁴ are λ₁, λ₂ and λ₃ respectively. Then

λ₂ = $\sqrt{λ_{1} λ_{3}}$
λ₂ = λ₁ + λ₃
λ₂ = λ₁ λ₂
λ₂= $\frac{λ_{1}}{λ_{3}}$

44.

Light with an energy flux of 18 W/cm² falls on a non-reflecting surface at normal incidence. The pressure exerted on the surface is

2 N/m²
2 × 10^-4 N/m²
6 N/m²
6 × 10^-4 N/m²

45.

The dimensional formula of Planck's constant is

[ M L² T^-1 ]
[ M L² T^-2 ]
[ M L⁰ T² ]
[ M L T² ]

46.

Which out of the following, cannot produce two coherent sources?

Lloyd's mirror
Fresnel biprism
Young's double slit
Prism

47.

In Young's double slit experiment, the two slits act as coherent sources of equal amplitude $α$ and of wavelength λ. In another experiment with the same set up, the two slits are sources of equal amplitude $α$ and wavelength λ, but are incoherent. The ratio of intensities of light at the midpoint of the screen in the first case to that in the second case is

2 : 1
1 : 2
3 : 4
4 : 3

48.

If the kinetic energy of a particle is increased by 16 times, the percentage change in the de Broglie wavelength of the particle is

25 %
75 %
60 %
50 %

49.

If the half lives of a radioactive element for $α$ and β decay are 4 years and 12 years respectively, the ratio of its initial activity and that after 12 years will be