JEE MAIN - Physics (2021 - 16th March Morning Shift)
- 1The pressure acting on a submarine is 3 $$\times$$ 105 Pa at a certain depth. If the depth is doubled, the percentage increase in the pressure acting on the submarine would be :
(Assume that atmospheric pressure is 1 $$\times$$ 105 Pa density of water is 103 kg m$$-$$3, g = 10 ms$$-$$2)Válasz(B)$${{200} \over 3}$$% - 3A block of mass m slides along a floor while a force of magnitude F is applied to it at an angle $$\theta$$ as shown in figure. The coefficient of kinetic friction is $$\mu$$k. then, the block's acceleration 'a' is given by :
(g is acceleration due to gravity)_16th_March_Morning_Shift_en_3_1.png)
Válasz(B)$${F \over m}\cos \theta - {\mu _K}\left( {g - {F \over m}\sin \theta } \right)$$ - 6The angle of deviation through a prism is minimum when
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(A) Incident ray and emergent ray are symmetric to the prism.
(B) The refracted ray inside the prism becomes parallel to its base
(C) Angle of incidence is equal to that of the angle of emergence
(D) When angle of emergence is double the angle of incidence
Choose the correct answer from the options given below :Válasz(C)Statements (A), (B) and (C) are true - 9For 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 :Válasz(C)$$C' = {{4K} \over {K + 3}}{C_0}$$
- 10A 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.Válasz(B)$$-$$24 $$\widehat x$$ V/m - 12A 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 :Válasz(C)$${1 \over 4}{{VA} \over {\rho l}}$$ - 17A conducting bar of length L is free to slide on two parallel conducting rails as shown in the figure
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Two resistors R1 and R2 are connected across the ends of the rails. There is a uniform magnetic field $$\overrightarrow B $$ pointing into the page. An external agent pulls the bar to the left at a constant speed v.
The correct statement about the directions of induced currents I1 and I2 flowing through R1 and R2 respectively is :Válasz(B)I1 is in clockwise direction and I2 is in anticlockwise direction - 22Consider a 20 kg uniform circular disk of radius 0.2 m. It is pin supported at its center and is at rest initially. The disk is acted upon by a constant force F = 20 N through a massless string wrapped around is periphery as shown in the figure.
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Suppose the disk makes n number of revolutions to attain an angular speed of 50 rad s$$-$$1.
The value of n, to the nearest integer, is __________.
[Given : In one complete revolution, the disk rotates by 6.28 rad]Válasz20 - 26A ball of mass 10 kg moving with a velocity $$10\sqrt 3 $$ m s$$-$$1 along X-axis, hits another ball of mass 20 kg which is at rest. After collision, the first ball comes to rest and the second one disintegrates into two equal pieces. One of the pieces starts moving along Y-axis at a speed of 10 m/s. The second piece starts moving at a speed of 20 m/s at an angle $$\theta$$ (degree) with respect to the X-axis.
The configuration of pieces after collision is shown in the figure.
The value of $$\theta$$ to the nearest integer is ____________._16th_March_Morning_Shift_en_26_1.png)
Válasz30 - 27The first three spectral lines of H-atom in the Balmer series are
given $$\lambda$$1, $$\lambda$$2, $$\lambda$$3 considering the Bohr atomic model, the wave lengths of first and third spectral lines $$\left( \frac{\lambda_{1} }{\lambda_{3} } \right) $$ are related by a factor of approximately 'x' $$\times$$ 10$$-$$1.
The value of x, to the nearest integer, is _________.Válasz15 - 28Consider a frame that is made up of two thin massless rods AB and AC as shown in the figure. A vertical force $$\overrightarrow P $$ of magnitude 100 N is applied at point A of the frame.
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Suppose the force is $$\overrightarrow P $$ resolved parallel to the arms AB and AC of the frame.
The magnitude of the resolved component along the arm AC is xN.
The value of x, to the nearest integer, is ___________.
[Given : sin(35$$^\circ$$) = 0.573, cos(35$$^\circ$$) = 0.819
sin(110$$^\circ$$) = 0.939, cos(110$$^\circ$$) = $$-$$ 0.342 JVálasz82
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