1
JEE Main 2020 (Online) 3rd September Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
Model a torch battery of length $$l$$ to be made up of a thin cylindrical bar of radius ‘a’ and a concentric thin cylindrical shell of radius ‘b’ filled in between with an electrolyte of resistivity $$\rho $$ (see figure). If the battery is connected to a resistance of value R, the maximum Joule heating in R will take place for : JEE Main 2020 (Online) 3rd September Morning Slot Physics - Current Electricity Question 183 English
A
$$R = {{2\rho } \over {\pi l}}\ln \left( {{b \over a}} \right)$$
B
$$R = {\rho \over {\pi l}}\ln \left( {{b \over a}} \right)$$
C
$$R = {\rho \over {2\pi l}}\ln \left( {{b \over a}} \right)$$
D
$$R = {\rho \over {2\pi l}}\left( {{b \over a}} \right)$$
2
JEE Main 2020 (Online) 3rd September Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
Moment of inertia of a cylinder of mass M, length L and radius R about an axis passing through its centre and perpendicular to the axis of the cylinder is
I = $$M\left( {{{{R^2}} \over 4} + {{{L^2}} \over {12}}} \right)$$. If such a cylinder is to be made for a given mass of a material, the ratio $${L \over R}$$ for it to have minimum possible I is
A
$${3 \over 2}$$
B
$$\sqrt {{3 \over 2}} $$
C
$$\sqrt {{2 \over 3}} $$
D
$${{2 \over 3}}$$
3
JEE Main 2020 (Online) 3rd September Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
When the wavelength of radiation falling on a metal is changed from 500 nm to 200 nm, the maximum kinetic energy of the photoelectrons becomes three times larger. The work function of the metal is close to :
A
1.02 eV
B
0.81 eV
C
0.61 eV
D
0.52 eV
4
JEE Main 2020 (Online) 3rd September Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
The magnetic field of a plane electromagnetic wave is
$$\overrightarrow B = 3 \times {10^{ - 8}}\sin \left[ {200\pi \left( {y + ct} \right)} \right]\widehat i$$ T
where c = 3 $$ \times $$ 108 ms–1 is the speed of light. The corresponding electric field is :
A
$$\overrightarrow E = - {10^{ - 6}}\sin \left[ {200\pi \left( {y + ct} \right)} \right]\widehat k$$ V/m
B
$$\overrightarrow E = - 9\sin \left[ {200\pi \left( {y + ct} \right)} \right]\widehat k$$ V/m
C
$$\overrightarrow E = 9\sin \left[ {200\pi \left( {y + ct} \right)} \right]\widehat k$$ V/m
D
$$\overrightarrow E = 3 \times {10^{ - 8}}\sin \left[ {200\pi \left( {y + ct} \right)} \right]\widehat k$$
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