WB JEE 2019 | Atoms and Nuclei Question 18 | Physics

A parent nucleus X undergoes $$\alpha$$-decay with a half-life of 75000 yrs. The daughter nucleus Y undergoes $$\beta$$-decay with a half-life of 9 months. In a particular sample, it is found that the rate of emission of $$\beta$$-particles is nearly constant (over several months) at $${10^7}/h$$. What will be the number of $$\alpha$$-particles emitted in an hour?

10²

10⁷

10¹²

10¹⁴

WB JEE 2019

MCQ (Single Correct Answer)

-0.25

A proton and an electron initially at rest are accelerated by the same potential difference. Assuming that a proton is 2000 times heavier than an electron, what will be the relation between the de Broglie wavelength of the proton ($$\lambda$$_p) and that of electron ($$\lambda$$_e)?

$$\lambda = 2000{\lambda _e}$$

$${\lambda _p} = {{{\lambda _e}} \over {2000}}$$

$${\lambda _p} = 20\sqrt 5 {\lambda _e}$$

$${\lambda _p} = {{{\lambda _e}} \over {20\sqrt 5 }}$$

WB JEE 2019

MCQ (Single Correct Answer)

-0.25

To which of the following the angular velocity of the electron in the n-th Bohr orbit is proportional?

$${n^2}$$

$${1 \over {{n^2}}}$$

$${1 \over {{n^{3/2}}}}$$

$${1 \over {{n^3}}}$$

WB JEE 2018

MCQ (Single Correct Answer)

-0.25

How the linear velocity v of an electron in the Bohr orbit is related to its quantum number n?

$$v \propto {1 \over n}$$

$$v \propto {1 \over {{n^2}}}$$

$$v \propto {1 \over {\sqrt n }}$$

$$v \propto n$$

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