1
JEE Main 2021 (Online) 26th August Morning Shift
+4
-1
The fractional change in the magnetic field intensity at a distance 'r' from centre on the axis of current carrying coil of radius 'a' to the magnetic field intensity at the centre of the same coil is : (Take r < a)
A
$${3 \over 2}{{{a^2}} \over {{r^2}}}$$
B
$${2 \over 3}{{{a^2}} \over {{r^2}}}$$
C
$${2 \over 3}{{{r^2}} \over {{a^2}}}$$
D
$${3 \over 2}{{{r^2}} \over {{a^2}}}$$
2
JEE Main 2021 (Online) 27th July Evening Shift
+4
-1
Figure A and B shown to long straight wires of circular cross-section (a and b with a < b), carrying current I which is uniformly distributed across the cross-section. The magnitude of magnetic field B varies with radius r and can be represented as :

A
B
C
D
3
JEE Main 2021 (Online) 25th July Evening Shift
+4
-1
Two ions having same mass have charges in the ratio 1 : 2. They are projected normally in a uniform magnetic field with their speeds in the ratio 2 : 3. The ratio of the radii of their circular trajectories is :
A
1 : 4
B
4 : 3
C
3 : 1
D
2 : 3
4
JEE Main 2021 (Online) 25th July Morning Shift
+4
-1
A linearly polarized electromagnetic wave in vacuum is

$$E = 3.1\cos \left[ {(1.8)z - (5.4 \times {{10}^6})t} \right]\widehat iN/C$$

is incident normally on a perfectly reflecting wall at z = a. Choose the correct option
A
The wavelength is 5.4 m
B
The frequency of electromagnetic wave is 54 $$\times$$ 104 Hz.
C
The transmitted wave will be $$3.1\cos \left[ {(1.8)z - (5.4 \times {{10}^6})t} \right]\widehat iN/C$$
D
The reflected wave will be $$3.1\cos \left[ {(1.8)z + (5.4 \times {{10}^6})t} \right]\widehat iN/C$$
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