1
JEE Main 2020 (Online) 8th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
In finding the electric field using Gauss Law the formula $$\left| {\overrightarrow E } \right| = {{{q_{enc}}} \over {{\varepsilon _0}\left| A \right|}}$$ is applicable. In the formula $${{\varepsilon _0}}$$ is permittivity of free space, A is the area of Gaussian surface and qenc is charge enclosed by the Gaussian surface. The equation can be used in which of the following situation?
A
Only when $$\left| {\overrightarrow E } \right|$$ = constant on the surface.
B
For any choice of Gaussian surface.
C
Only when the Gaussian surface is an equipotential surface.
D
Only when the Gaussian surface is an equipotential surface and $$\left| {\overrightarrow E } \right|$$ is constant on the surface.
2
JEE Main 2020 (Online) 8th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
When photon of energy 4.0 eV strikes the surface of a metal A, the ejected photoelectrons have maximum kinetic energy TA eV end de-Broglie wavelength $$\lambda _A$$. The maximum kinetic energy of photoelectrons liberated from another metal B by photon of energy 4.50 eV is TB = (TA – 1.5) eV. If the de-Broglie wavelength of these photoelectrons $$\lambda _B$$ = 2$$\lambda _A$$, then the work function of metal B is :
A
1.5eV
B
4eV
C
2eV
D
3eV
3
JEE Main 2020 (Online) 8th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
The coordinates of centre of mass of a uniform flag shaped lamina (thin flat plate) of mass 4kg. (The coordinates of the same are shown in figure) are : JEE Main 2020 (Online) 8th January Morning Slot Physics - Center of Mass and Collision Question 82 English
A
(0.75m, 1.75m)
B
(1m, 1.75m)
C
(0.75m, 0.75m)
D
(1.25m, 1.50m)
4
JEE Main 2020 (Online) 8th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
Consider a uniform rod of mass M = 4m and length $$\ell $$ pivoted about its centre. A mass m moving with velocity v making angle $$\theta = {\pi \over 4}$$ to the rod's long axis collides with one end of the rod and sticks to it. The angular speed of the rod-mass system just after the collision is :
A
$${{3\sqrt 2 } \over 7}{v \over \ell }$$
B
$${3 \over 7}{v \over \ell }$$
C
$${3 \over {7\sqrt 2 }}{v \over \ell }$$
D
$${4 \over 7}{v \over \ell }$$
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