1
JEE Main 2021 (Online) 16th March Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
For changing the capacitance of a given parallel plate capacitor, a dielectric material of dielectric constant K is used, which has the same area as the plates of the capacitor. The thickness of the dielectric slab is $${3 \over 4}$$d, where 'd' is the separation between the plates of parallel plate capacitor. The new capacitance (C') in terms of original capacitance (C0) is given by the following relation :
A
$$C' = {{3 + K} \over {4K}}{C_0}$$
B
$$C' = {{4 + K} \over {3}}{C_0}$$
C
$$C' = {{4K} \over {K + 3}}{C_0}$$
D
$$C' = {{4} \over {3 + K}}{C_0}$$
2
JEE Main 2021 (Online) 16th March Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
A plane electromagnetic wave of frequency 500 MHz is travelling in vacuum along y-direction. At a particular point in space and time,
$$\overrightarrow B $$ = 8.0 $$\times$$ 10$$-$$8 $$\widehat z$$T. The value of electric field at this point is :

(speed of light = 3 $$\times$$ 108 ms$$-$$1)

$$\widehat x$$, $$\widehat y$$, $$\widehat z$$ are unit vectors along x, y and z directions.
A
2.6 $$\widehat x$$ V/m
B
$$-$$24 $$\widehat x$$ V/m
C
24 $$\widehat x$$ V/m
D
$$-$$2.6 $$\widehat y$$ V/m
3
JEE Main 2021 (Online) 16th March Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
The maximum and minimum distances of a comet from the Sun are 1.6 $$\times$$ 1012 m and 8.0 $$\times$$ 1010 m respectively. If the speed of the comet at the nearest point is 6 $$\times$$ 104 ms$$-$$1, the speed at the farthest point is :
A
3.0 $$\times$$ 103 m/s
B
6.0 $$\times$$ 103 m/s
C
1.5 $$\times$$ 103 m/s
D
4.5 $$\times$$ 103 m/s
4
JEE Main 2021 (Online) 16th March Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
A conducting wire of length 'l', area of cross-section A and electric resistivity $$\rho$$ is connected between the terminals of a battery. A potential difference V is developed between its ends, causing an electric current.

If the length of the wire of the same material is doubled and the area of cross-section is halved, the resultant current would be :
A
$$4{{VA} \over {\rho l}}$$
B
$${3 \over 4}{{VA} \over {\rho l}}$$
C
$${1 \over 4}{{VA} \over {\rho l}}$$
D
$${1 \over 4}{{\rho l} \over {VA}}$$
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