1
JEE Main 2018 (Online) 15th April Morning Slot
+4
-1
Two electrons are moving with non-relativistic speed perpendicular to each other. If corresponding de Broglie wavelength are $${\lambda _1}$$ and $${\lambda _2},$$ their de Broglie wavelength in the frame of reference attached to their center of masses :
A
$${\lambda _{CM}} = {\lambda _1} = {\lambda _2}$$
B
$${\lambda _{CM}} = {{2{\lambda _1}{\lambda _2}} \over {\sqrt {\lambda _1^2 + \lambda _2^2} }}$$
C
$${1 \over {{\lambda _{CM}}}} = {1 \over {{\lambda _1}}} + {1 \over {{\lambda _2}}}$$
D
$${\lambda _{CM}} = \left( {{{{\lambda _1} + {\lambda _2}} \over 2}} \right)$$
2
JEE Main 2017 (Online) 9th April Morning Slot
+4
-1
A Laser light of wavelength 660 nm is used to weld Retina detachment. If a Laser pulse of width 60 ms and power 0.5 kW is used the approximate number of photons in the pulse are :

[Take Planck's constant h $$=$$ 6.62 $$\times$$ 10$$-$$34 Js]
A
1020
B
1018
C
1022
D
1019
3
JEE Main 2017 (Online) 8th April Morning Slot
+4
-1
The maximum velocity of the photoelectrons emitted from the surface is v when light of frequency n falls on a metal surface. If the incident frequency is increased to 3n, the maximum velocity of the ejected photoelectrons will be :
A
less than $$\sqrt 3$$ v
B
v
C
more than $$\sqrt 3 \,v$$
D
equal to $$\sqrt 3 \,v$$
4
JEE Main 2017 (Offline)
+4
-1
An electron beam is accelerated by a potential difference V to hit a metallic target to produce X–rays. It produces continuous as well as characteristic X-rays. If $$\lambda$$min is the smallest possible wavelength of X-ray in the spectrum, the variation of log$$\lambda$$min with log V is correctly represented in:
A
B
C
D
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