1
WB JEE 2019
MCQ (Single Correct Answer)
+1
-0.25
Change Language
A ray of light is reflected by a plane mirror. $${\widehat e_0}$$, $$\widehat e$$ and $$\widehat n$$ be the unit vectors along the incident ray, reflected ray and the normal to the reflecting surface respectively.

Which of the following gives an expression for $$\widehat e$$?

WB JEE 2019 Physics - Geometrical Optics Question 19 English
A
$${\widehat e_0} + 2({\widehat e_0}.\,\widehat n)\widehat n$$
B
$${\widehat e_0} - 2({\widehat e_0}.\,\widehat n)\widehat n$$
C
$${\widehat e_0} - ({\widehat e_0}.\,\widehat n)\widehat n$$
D
$${\widehat e_0} + ({\widehat e_0}.\,\widehat n)\widehat n$$
2
WB JEE 2019
MCQ (Single Correct Answer)
+1
-0.25
Change Language
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?
A
102
B
107
C
1012
D
1014
3
WB JEE 2019
MCQ (Single Correct Answer)
+1
-0.25
Change Language
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)?
A
$$\lambda = 2000{\lambda _e}$$
B
$${\lambda _p} = {{{\lambda _e}} \over {2000}}$$
C
$${\lambda _p} = 20\sqrt 5 {\lambda _e}$$
D
$${\lambda _p} = {{{\lambda _e}} \over {20\sqrt 5 }}$$
4
WB JEE 2019
MCQ (Single Correct Answer)
+1
-0.25
Change Language
To which of the following the angular velocity of the electron in the n-th Bohr orbit is proportional?
A
$${n^2}$$
B
$${1 \over {{n^2}}}$$
C
$${1 \over {{n^{3/2}}}}$$
D
$${1 \over {{n^3}}}$$
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