An object of weight \[W\] and density\[\rho \] is dipped in a fluid of density \[{{\rho }_{1}}\]. Its apparent weight will be

\[\frac{(\rho -{{\rho }_{1}})}{W}\]

\[W\left( 1-\frac{{{\rho }_{1}}}{\rho } \right)\]

\[\frac{(\rho -{{\rho }_{1}})}{W}\]

Assertion : The water rises higher in a capillary tube of small diameter than in the capillary tube of large diameter. Reason : Height through which liquid rises in a capillary tube is inversely proportional to the diameter of the capillary tube.

If both assertion and reason are true but reason is not the correct explanation of the assertion.

If both assertion and reason are true and the reason is the correct explanation of the assertion.

If both assertion and reason are true but reason is not the correct explanation of the assertion.

If assertion is true but reason is false.

If the assertion and reason both are false.

In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of \[2.0\text{ }\times \text{ }{{10}^{10}}\] Hz and amplitude \[48\,V\,{{m}^{-1}}\]. Then

the wavelength of the wave is \[1.5\times {{10}^{-5}}\text{ }m\]

the amplitude of the oscillating magnetic field is \[16\times {{10}^{-3}}T\]

the average energy density of the E is equal to the average energy density of the B. \[[c=3\times {{10}^{8}}\,m\,{{s}^{-1}}.]\]

An EM wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure p on it. Which of the following is wrong?

Radiation pressure is \[\frac{2I}{c}\] if the wave is totally reflected

Radiation pressure is \[\frac{I}{c}\] if the wave is totally absorbed

Radiation pressure is \[\frac{I}{c}\] if the wave is totally reflected

Radiation pressure is \[\frac{2I}{c}\] if the wave is totally reflected

Radiation pressure is in the range \[\frac{I}{c}

The charge on a parallel plate capacitor varies as \[q={{q}_{0}}\,\cos \,2\pi vt\]. The plates are very large and close together (area = A, separation = d). Neglecting the edge effects, the displacement current through the capacitor is

\[3/5\pi v{{q}_{0}}\,\sin \,\pi vt\]

\[2\pi v{{q}_{0}}\,\sin \,2\pi vt\]

\[3/5\pi v{{q}_{0}}\,\sin \,\pi vt\]

\[4\pi v{{q}_{0}}\,\sin \,2\pi vt\]

The rms value of the electric field of the light coming from the Sun is\[720\text{ }N/C\]. The average total energy density of the electromagnetic wave is

\[6.37\times {{10}^{-9}}J/{{m}^{3}}\]

\[4.58\times {{10}^{-6}}J/{{m}^{3}}\]

\[6.37\times {{10}^{-9}}J/{{m}^{3}}\]

\[81.35\times {{10}^{-12}}J/{{m}^{3}}\]

\[3.3\times {{10}^{-3}}J/{{m}^{3}}\]

Given below is a list of electromagnetic spectrum and its mode of production. Which one does not match?

Gamma rays - Radioactive decay of the nucleus

Ultraviolet rays - Magnetron valve

Radio wave - Rapid acceleration and deceleration of electrons in conducting wires

If c is the speed of electromagnetic waves in vacuum, its speed in a medium of dielectric constant K and relative permeability \[{{\mu }_{r}}\] is

\[v=\frac{K}{\sqrt{{{\mu }_{r}}C}}\]

\[v=\frac{1}{\sqrt{{{\mu }_{r}}K}}\]

\[v=\frac{c}{\sqrt{{{\mu }_{r}}K}}\]

\[v=\frac{K}{\sqrt{{{\mu }_{r}}C}}\]

If \[{{\varepsilon }_{0}}\] and \[{{\mu }_{0}}\] are the electric permittivity and magnetic permeability in vacuum, \[\varepsilon \] and \[\mu \] are corresponding quantities in medium, then refractive index of the medium is

\[\sqrt{\frac{\varepsilon }{{{\varepsilon }_{0}}}}\]

\[\sqrt{\frac{{{\varepsilon }_{0}}\mu }{\varepsilon {{\mu }_{0}}}}\]

\[\sqrt{\frac{{{\varepsilon }_{0}}{{\mu }_{0}}}{\varepsilon \mu }}\]

\[\sqrt{\frac{\varepsilon \mu }{{{\varepsilon }_{0}}{{\mu }_{0}}}}\]

The magnetic field in the plane electromagnetic field is given by: \[{{B}_{y}}=2\times {{10}^{-7}}\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)T\] The expression for the electric field may be given by

\[{{E}_{y}}=2\times {{10}^{-7}}\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)V/m\]

\[{{E}_{x}}=2\times {{10}^{-7}}\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)V/m\]

\[{{E}_{y}}=60\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)V/m\]

\[{{E}_{x}}=60\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)V/m\]

The rms value of the electric field of the light coming from sun is 720 N/C. The average energy density of the emf is

\[6.37\times {{10}^{-9}}J/{{m}^{3}}\]

\[3.3\times {{10}^{-3}}J/{{m}^{3}}\]

\[4.58\times {{10}^{-6}}J/{{m}^{3}}\]

\[6.37\times {{10}^{-9}}J/{{m}^{3}}\]

\[81.35\times {{10}^{-12}}J/{{m}^{3}}\]

A series combination of \[{{n}_{1}}\] capacitors, each of capacity \[{{C}_{1}}\] is charged by source of potential difference 4 V. When another parallel combination of \[{{n}_{2}}\]capacitors each of capacity \[{{C}_{2}}\]is charged by a source of potential deference V, it has the same total energy stored in it as the first combination has. The value of \[{{C}_{2}}\]in terms of \[{{C}_{1}}\]is then

\[16\frac{{{n}_{2}}}{{{n}_{1}}}{{C}_{1}}\]

\[\frac{2{{C}_{1}}}{{{n}_{1}}{{n}_{2}}}\]

\[2\frac{{{n}_{1}}}{{{n}_{2}}}{{C}_{1}}\]

\[\frac{16{{C}_{1}}}{{{n}_{1}}{{n}_{2}}}\]

The resultant capacity of n condensers of capacitances \[{{C}_{1}},{{C}_{2}}\ldots .{{C}_{n}}\]connected in parallel is

\[{{C}_{p}}={{C}_{1}}-{{C}_{2}}-\ldots .-{{C}_{n}}\]

\[{{C}_{p}}={{C}_{1}}+{{C}_{2}}+\ldots .+{{C}_{n}}\]

\[{{C}_{p}}={{C}_{1}}-{{C}_{2}}-\ldots .-{{C}_{n}}\]

\[\frac{1}{{{C}_{p}}}=\frac{1}{{{C}_{1}}}+\frac{1}{{{C}_{2}}}+\ldots .+\frac{1}{{{C}_{n}}}\]

\[\frac{1}{{{C}_{p}}}=\frac{1}{{{C}_{1}}}-\frac{1}{{{C}_{2}}}-\ldots .-\frac{1}{{{C}_{n}}}\]

An electric dipole is put in north-south direction in a sphere filled with water. Which statement is correct?

Water does not permit electric flux to enter into sphere.

Electric flux is coming towards sphere.

Electric flux is coming out of sphere.

Electric flux is entering into sphere and leaving the sphere are same.

Water does not permit electric flux to enter into sphere.

A sphere of radius R carries charge density \[\rho \]proportional to the square of the distance from the center such that \[\rho =C{{R}^{2}}\], where C is a positive constant. At a distance R/2 from the center, the magnitude of the electric field is

\[\frac{C{{R}^{3}}}{20{{\in }_{0}}}\]

\[\frac{C{{R}^{3}}}{10{{\in }_{0}}}\]

\[\frac{C{{R}^{3}}}{5{{\in }_{0}}}\]

\[\frac{C{{R}^{3}}}{40{{\in }_{0}}}\]

The total electric flux emanating from a closed surface enclosing an \[\alpha -\]particle is (e-electronic charge)

\[\frac{e}{{{\varepsilon }_{0}}}\]

\[\frac{2e}{{{\varepsilon }_{0}}}\]

\[\frac{e}{{{\varepsilon }_{0}}}\]

\[\frac{{{\varepsilon }_{0}}e}{4}\]

Three identical positive charges Q are arranged of the triangle is a. Find the intensity of the field at the vertex of a regular tetrahedron of which the triangle is the base.

\[\sqrt{2}\frac{KQ}{{{a}^{2}}}\]

\[\sqrt{6}\frac{KQ}{{{a}^{2}}}\]

\[\sqrt{2}\frac{KQ}{{{a}^{2}}}\]

\[\sqrt{3}\frac{KQ}{{{a}^{2}}}\]

Find the electric field vector at P (a, a, a) due to three infinitely long lines of charges along the x, y and z- axes, respectively. The charge density, i.e., charge per unit length of each wire is \[\lambda .\]

\[\frac{\lambda }{2\sqrt{2}\pi {{\varepsilon }_{0}}a}\left( \hat{i}+\hat{j}+\hat{k} \right)\]

\[\frac{\lambda }{3\pi {{\varepsilon }_{0}}a}\left( \hat{i}+\hat{j}+\hat{k} \right)\]

\[\frac{\lambda }{2\pi {{\varepsilon }_{0}}a}\left( \hat{i}+\hat{j}+\hat{k} \right)\]

\[\frac{\lambda }{2\sqrt{2}\pi {{\varepsilon }_{0}}a}\left( \hat{i}+\hat{j}+\hat{k} \right)\]

\[\frac{\sqrt{2}\lambda }{\pi {{\varepsilon }_{0}}a}\left( \hat{i}+\hat{j}+\hat{k} \right)\]

A pendulum bob of mass m carrying a charge q is at rest with its string making and angle \[\theta \] with the vertical in a uniform horizontal electric field E. The tension in the string is

\[\frac{mg}{\cos \theta }\text{ and }\frac{qE}{\sin \theta }\]

\[\frac{mg}{\sin \theta }\text{ and }\frac{qE}{\cos \theta }\]

\[\frac{mg}{\cos \theta }\text{ and }\frac{qE}{\sin \theta }\]

Two point dipoles of dipole moment \[{{\vec{p}}_{1}}\]and \[{{\vec{p}}_{2}}\]are at a distance x from each other and \[{{\vec{p}}_{1}}||{{\vec{p}}_{2}}.\] The force between the dipoles is:

\[\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{6{{p}_{1}}{{p}_{2}}}{{{x}^{4}}}\]

\[\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{4{{p}_{1}}{{p}_{2}}}{{{x}^{4}}}\]

\[\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{3{{p}_{1}}{{p}_{2}}}{{{x}^{4}}}\]

\[\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{6{{p}_{1}}{{p}_{2}}}{{{x}^{4}}}\]

\[\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{8{{p}_{1}}{{p}_{2}}}{{{x}^{4}}}\,\]

A uniformly charged and infinitely long line having a liner charge density \[\lambda \] is placed at a normal distance \[y\] from a point O. Consider a sphere of radius \[R\] with O as the center and \[R\] > \[y\]. Electric flux through the surface of the sphere is

\[\frac{\lambda \sqrt{{{R}^{2}}+{{y}^{2}}}}{{{\varepsilon }_{0}}}\]

\[\frac{2\lambda R}{{{\varepsilon }_{0}}}\]

\[\frac{2\lambda \sqrt{{{R}^{2}}-{{y}^{2}}}}{{{\varepsilon }_{0}}}\]

\[\frac{\lambda \sqrt{{{R}^{2}}+{{y}^{2}}}}{{{\varepsilon }_{0}}}\]

An uncharged aluminum block has a cavity within it. The block is placed in a region where a uniform electric field is directed upward. Which of the following is a correct statement describing conditions in the interior of the block's cavity?

The electric field in the cavity is of varying magnitude and is zero at the exact center.

The electric field in the cavity is directed upward.

The electric field in the cavity is directed downward.

There is no electric field in the cavity.

The electric field in the cavity is of varying magnitude and is zero at the exact center.

12583 + Mcqs in Physics in Joint Entrance Exam - Main (JEE Main) Page 248 McqOptions

12351.	Two solids A and B float in water. It is observed that A floats with \[\frac{1}{2}\] of its body immersed in water and B floats with \[\frac{1}{4}\] of its volume above the water level. The ratio of the density of A to that of B is
A.	4 : 3
B.	2 : 3
C.	3 : 4
D.	1 : 2
Answer» C. 3 : 4

Discussion

12352.	A hollow sphere of volume V is floating on water surface with half immersed in it. What should be the minimum volume of water poured inside the sphere so that the sphere now sinks into the water
A.	\[V/2\]
B.	\[V/3\]
C.	\[V/4\]
D.	V
Answer» B. \[V/3\]

Discussion

12353.	Pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel. This law was first formulated by
A.	Bernoulli
B.	Archimedes
C.	Boyle
D.	Pascal
Answer» E.

Discussion

12354.	An object of weight \[W\] and density\[\rho \] is dipped in a fluid of density \[{{\rho }_{1}}\]. Its apparent weight will be
A.	\[W(\rho -{{\rho }_{1}})\]
B.	\[W\left( 1-\frac{{{\rho }_{1}}}{\rho } \right)\]
C.	\[\frac{(\rho -{{\rho }_{1}})}{W}\]
D.	\[W(\rho -{{\rho }_{1}})\]
Answer» C. \[\frac{(\rho -{{\rho }_{1}})}{W}\]

Discussion

12355.	A metallic block weighs 15 N in air. It weighs 12 N when immersed in water and 13 N when immersed in another liquid. What is the specific gravity of the liquid?
A.	44256
B.	44257
C.	41609
D.	13/15
Answer» C. 41609

Discussion

12356.	Assertion : The water rises higher in a capillary tube of small diameter than in the capillary tube of large diameter. Reason : Height through which liquid rises in a capillary tube is inversely proportional to the diameter of the capillary tube.
A.	If both assertion and reason are true and the reason is the correct explanation of the assertion.
B.	If both assertion and reason are true but reason is not the correct explanation of the assertion.
C.	If assertion is true but reason is false.
D.	If the assertion and reason both are false.
Answer» B. If both assertion and reason are true but reason is not the correct explanation of the assertion.

Discussion

12357.	A square plate of 0.1 m side moves parallel to a second plate with a velocity of 0.1 m/s, both plates being immersed in water. If the viscous force is 0.002 N and the coefficient of viscosity is 0.01 poise, distance between the plates in m is [EAMCET (Med.) 2003]
A.	0.1
B.	0.05
C.	0.005
D.	0.0005
Answer» E.

Discussion

12358.	When a body falls in air, the resistance of air depends to a great extent on the shape of the body, 3 different shapes are given. Identify the combination of air resistances which truly represents the physical situation. (The cross sectional areas are the same). [KCET 2005]
A.	1 < 2 < 3
B.	2 < 3 < 1
C.	3 < 2 < 1
D.	3 < 1 < 2
Answer» D. 3 < 1 < 2

Discussion

12359.	In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of \[2.0\text{ }\times \text{ }{{10}^{10}}\] Hz and amplitude \[48\,V\,{{m}^{-1}}\]. Then
A.	the wavelength of the wave is \[1.5\times {{10}^{-5}}\text{ }m\]
B.	the amplitude of the oscillating magnetic field is \[16\times {{10}^{-3}}T\]
C.	the average energy density of the E is equal to the average energy density of the B. \[[c=3\times {{10}^{8}}\,m\,{{s}^{-1}}.]\]
D.	None of these
Answer» D. None of these

Discussion

12360.	An EM wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure p on it. Which of the following is wrong?
A.	Radiation pressure is \[\frac{I}{c}\] if the wave is totally absorbed
B.	Radiation pressure is \[\frac{I}{c}\] if the wave is totally reflected
C.	Radiation pressure is \[\frac{2I}{c}\] if the wave is totally reflected
D.	Radiation pressure is in the range \[\frac{I}{c}<p<\frac{2I}{c}\] for real surfaces
Answer» C. Radiation pressure is \[\frac{2I}{c}\] if the wave is totally reflected

Discussion

12361.	The charge on a parallel plate capacitor varies as \[q={{q}_{0}}\,\cos \,2\pi vt\]. The plates are very large and close together (area = A, separation = d). Neglecting the edge effects, the displacement current through the capacitor is
A.	\[2\pi v{{q}_{0}}\,\sin \,2\pi vt\]
B.	\[3/5\pi v{{q}_{0}}\,\sin \,\pi vt\]
C.	\[4\pi v{{q}_{0}}\,\sin \,2\pi vt\]
D.	None of these
Answer» B. \[3/5\pi v{{q}_{0}}\,\sin \,\pi vt\]

Discussion

12362.	The ratio of contributions made by the electric field and magnetic field components to the intensity of an EM wave is
A.	\[c:1\]
B.	\[{{c}^{2}}:1\]
C.	\[1:1\]
D.	\[\sqrt{c}:1\]
Answer» D. \[\sqrt{c}:1\]

Discussion

12363.	The rms value of the electric field of the light coming from the Sun is\[720\text{ }N/C\]. The average total energy density of the electromagnetic wave is
A.	\[4.58\times {{10}^{-6}}J/{{m}^{3}}\]
B.	\[6.37\times {{10}^{-9}}J/{{m}^{3}}\]
C.	\[81.35\times {{10}^{-12}}J/{{m}^{3}}\]
D.	\[3.3\times {{10}^{-3}}J/{{m}^{3}}\]
Answer» B. \[6.37\times {{10}^{-9}}J/{{m}^{3}}\]

Discussion

12364.	Given below is a list of electromagnetic spectrum and its mode of production. Which one does not match?
A.	Gamma rays - Radioactive decay of the nucleus
B.	Ultraviolet rays - Magnetron valve
C.	Radio wave - Rapid acceleration and deceleration of electrons in conducting wires
D.	X-rays - coolidge tube
Answer» E.

Discussion

12365.	The waves which are electromagnetic in nature are
A.	sound waves and light waves
B.	water waves and radio waves
C.	light waves and X-rays
D.	sound waves and water waves
Answer» D. sound waves and water waves

Discussion

12366.	A plane electromagnetic wave is incident on a plane surface of area A, normally and is perfectly reflected. If energy E strikes the surface in time t then force exerted on the surface is (c =speed of light)
A.	\[\frac{2E}{Atc}\]
B.	\[\frac{E}{2c}\]
C.	\[\frac{2E}{ct}\]
D.	zero
Answer» D. zero

Discussion

12367.	In an apparatus, the electric field was found to oscillate with an amplitude of\[18\text{ }V/m\]. The magnitude of the oscillating magnetic field will be
A.	\[4\times {{10}^{-6}}T\]
B.	\[6\times {{10}^{-8}}T\]
C.	\[9\times {{10}^{-9}}T\]
D.	\[11\times {{10}^{-11}}T\]
Answer» C. \[9\times {{10}^{-9}}T\]

Discussion

12368.	If c is the speed of electromagnetic waves in vacuum, its speed in a medium of dielectric constant K and relative permeability \[{{\mu }_{r}}\] is
A.	\[v=\frac{1}{\sqrt{{{\mu }_{r}}K}}\]
B.	\[v=c\sqrt{{{\mu }_{r}}K}\]
C.	\[v=\frac{c}{\sqrt{{{\mu }_{r}}K}}\]
D.	\[v=\frac{K}{\sqrt{{{\mu }_{r}}C}}\]
Answer» D. \[v=\frac{K}{\sqrt{{{\mu }_{r}}C}}\]

Discussion

12369.	If \[{{\varepsilon }_{0}}\] and \[{{\mu }_{0}}\] are the electric permittivity and magnetic permeability in vacuum, \[\varepsilon \] and \[\mu \] are corresponding quantities in medium, then refractive index of the medium is
A.	\[\sqrt{\frac{\varepsilon }{{{\varepsilon }_{0}}}}\]
B.	\[\sqrt{\frac{{{\varepsilon }_{0}}\mu }{\varepsilon {{\mu }_{0}}}}\]
C.	\[\sqrt{\frac{{{\varepsilon }_{0}}{{\mu }_{0}}}{\varepsilon \mu }}\]
D.	\[\sqrt{\frac{\varepsilon \mu }{{{\varepsilon }_{0}}{{\mu }_{0}}}}\]
Answer» E.

Discussion

12370.	The magnetic field in the plane electromagnetic field is given by: \[{{B}_{y}}=2\times {{10}^{-7}}\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)T\] The expression for the electric field may be given by
A.	\[{{E}_{y}}=2\times {{10}^{-7}}\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)V/m\]
B.	\[{{E}_{x}}=2\times {{10}^{-7}}\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)V/m\]
C.	\[{{E}_{y}}=60\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)V/m\]
D.	\[{{E}_{x}}=60\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)V/m\]
Answer» E.

Discussion

12371.	The rms value of the electric field of the light coming from sun is 720 N/C. The average energy density of the emf is
A.	\[3.3\times {{10}^{-3}}J/{{m}^{3}}\]
B.	\[4.58\times {{10}^{-6}}J/{{m}^{3}}\]
C.	\[6.37\times {{10}^{-9}}J/{{m}^{3}}\]
D.	\[81.35\times {{10}^{-12}}J/{{m}^{3}}\]
Answer» C. \[6.37\times {{10}^{-9}}J/{{m}^{3}}\]

Discussion

12372.	The work function of a metallic surface is 5.01 eV. The photoelectrons are emitted when light of wavelength 2000 \[\overset{\text{o}}{\mathop{\text{A}}}\,\] falls on it. The potential difference applied to stop! The fastest photoelectrons is \[\left[ h=4.14\times {{10}^{-15}}eVs \right]\]
A.	1.2 V
B.	2.24 V
C.	3.6 V
D.	4.8 V
Answer» B. 2.24 V

Discussion

12373.	An electron is accelerated through a potential difference of V volt. It has a wavelength \[\lambda \] associated with it. Through what potential difference an electron must be accelerated so that its de Broglie wavelength is the same as that of a Proton? Take mass of proton to be 1837 times larger than the mass of electron.
A.	\[Vvolt\]
B.	\[1837V\,volt\]
C.	\[V/1837\,volt\]
D.	\[\sqrt{1837}V\,volt\]
Answer» D. \[\sqrt{1837}V\,volt\]

Discussion

12374.	A parallel plate capacitor with plate area A and separation between the plates J, is charged by a constant current i. Consider a plane surface of area all parallel to the plates and drawn simultaneously between the plates. The displacement current through this area is
A.	\[i\]
B.	\[i/2\]
C.	\[i/4\]
D.	\[i/8\]
Answer» C. \[i/4\]

Discussion

12375.	In the circuit shown, the effective capacitano between points X and Y is
A.	\[3.33\mu F\]
B.	\[1\mu F\]
C.	\[0.44\mu F\]
D.	None of these
Answer» C. \[0.44\mu F\]

Discussion

12376.	A series combination of \[{{n}_{1}}\] capacitors, each of capacity \[{{C}_{1}}\] is charged by source of potential difference 4 V. When another parallel combination of \[{{n}_{2}}\]capacitors each of capacity \[{{C}_{2}}\]is charged by a source of potential deference V, it has the same total energy stored in it as the first combination has. The value of \[{{C}_{2}}\]in terms of \[{{C}_{1}}\]is then
A.	\[16\frac{{{n}_{2}}}{{{n}_{1}}}{{C}_{1}}\]
B.	\[\frac{2{{C}_{1}}}{{{n}_{1}}{{n}_{2}}}\]
C.	\[2\frac{{{n}_{1}}}{{{n}_{2}}}{{C}_{1}}\]
D.	\[\frac{16{{C}_{1}}}{{{n}_{1}}{{n}_{2}}}\]
Answer» E.

Discussion

12377.	A parallel plate capacitor with air between the plates is charged to a potential difference of 500 V and then insulated. A plastic plate is inserted between the plates filling the whole gap. The potential difference between the plates now becomes 75V. The dielectric constant of plastic is
A.	44265
B.	5
C.	44275
D.	10
Answer» D. 10

Discussion

12378.	The resultant capacity of n condensers of capacitances \[{{C}_{1}},{{C}_{2}}\ldots .{{C}_{n}}\]connected in parallel is
A.	\[{{C}_{p}}={{C}_{1}}+{{C}_{2}}+\ldots .+{{C}_{n}}\]
B.	\[{{C}_{p}}={{C}_{1}}-{{C}_{2}}-\ldots .-{{C}_{n}}\]
C.	\[\frac{1}{{{C}_{p}}}=\frac{1}{{{C}_{1}}}+\frac{1}{{{C}_{2}}}+\ldots .+\frac{1}{{{C}_{n}}}\]
D.	\[\frac{1}{{{C}_{p}}}=\frac{1}{{{C}_{1}}}-\frac{1}{{{C}_{2}}}-\ldots .-\frac{1}{{{C}_{n}}}\]
Answer» B. \[{{C}_{p}}={{C}_{1}}-{{C}_{2}}-\ldots .-{{C}_{n}}\]

Discussion

12379.	When air in a capacitor is replaced by medium of dielectric constant K, the capacity
A.	decrease K times
B.	increases K times
C.	increases \[{{K}^{2}}\]times
D.	remains constant
Answer» C. increases \[{{K}^{2}}\]times

Discussion

12380.	A hollow metal sphere of radius 5 cm is charged such that the potential on its surface is 10 V. The potential at a distance of 2 cm from the center of the sphere is
A.	zero
B.	10 V
C.	4 V
D.	10/3 V
Answer» C. 4 V

Discussion

12381.	An electric dipole is put in north-south direction in a sphere filled with water. Which statement is correct?
A.	Electric flux is coming towards sphere.
B.	Electric flux is coming out of sphere.
C.	Electric flux is entering into sphere and leaving the sphere are same.
D.	Water does not permit electric flux to enter into sphere.
Answer» D. Water does not permit electric flux to enter into sphere.

Discussion

12382.	A surface has the area vector \[\vec{A}=\left( 2\hat{i}+3\hat{j} \right){{m}^{2}}.\] The flux of an electric field through it if the field is \[\vec{E}=4\hat{i}\frac{V}{m}:\]
A.	8V-m
B.	12Vm
C.	20V-m
D.	zero
Answer» B. 12Vm

Discussion

12383.	A sphere of radius R carries charge density \[\rho \]proportional to the square of the distance from the center such that \[\rho =C{{R}^{2}}\], where C is a positive constant. At a distance R/2 from the center, the magnitude of the electric field is
A.	\[\frac{C{{R}^{3}}}{20{{\in }_{0}}}\]
B.	\[\frac{C{{R}^{3}}}{10{{\in }_{0}}}\]
C.	\[\frac{C{{R}^{3}}}{5{{\in }_{0}}}\]
D.	\[\frac{C{{R}^{3}}}{40{{\in }_{0}}}\]
Answer» E.

Discussion

12384.	The total electric flux emanating from a closed surface enclosing an \[\alpha -\]particle is (e-electronic charge)
A.	\[\frac{2e}{{{\varepsilon }_{0}}}\]
B.	\[\frac{e}{{{\varepsilon }_{0}}}\]
C.	\[e{{\varepsilon }_{0}}\]
D.	\[\frac{{{\varepsilon }_{0}}e}{4}\]
Answer» B. \[\frac{e}{{{\varepsilon }_{0}}}\]

Discussion

12385.	A solid sphere of radius R has a charge Q distributed in its volume with a charge density\[\rho =k{{r}^{a}}\], where k and an are constants and r is the distance from its center. If the electric field at \[r=\frac{R}{2}\] is \[\frac{1}{8}\] times that at \[r=R\], the value of a is.
A.	3
B.	5
C.	2
D.	both [a] and [b]
Answer» D. both [a] and [b]

Discussion

12386.	Three identical positive charges Q are arranged of the triangle is a. Find the intensity of the field at the vertex of a regular tetrahedron of which the triangle is the base.
A.	\[\sqrt{6}\frac{KQ}{{{a}^{2}}}\]
B.	\[\sqrt{2}\frac{KQ}{{{a}^{2}}}\]
C.	\[\sqrt{3}\frac{KQ}{{{a}^{2}}}\]
D.	None of these
Answer» B. \[\sqrt{2}\frac{KQ}{{{a}^{2}}}\]

Discussion

12387.	Find the electric field vector at P (a, a, a) due to three infinitely long lines of charges along the x, y and z- axes, respectively. The charge density, i.e., charge per unit length of each wire is \[\lambda .\]
A.	\[\frac{\lambda }{3\pi {{\varepsilon }_{0}}a}\left( \hat{i}+\hat{j}+\hat{k} \right)\]
B.	\[\frac{\lambda }{2\pi {{\varepsilon }_{0}}a}\left( \hat{i}+\hat{j}+\hat{k} \right)\]
C.	\[\frac{\lambda }{2\sqrt{2}\pi {{\varepsilon }_{0}}a}\left( \hat{i}+\hat{j}+\hat{k} \right)\]
D.	\[\frac{\sqrt{2}\lambda }{\pi {{\varepsilon }_{0}}a}\left( \hat{i}+\hat{j}+\hat{k} \right)\]
Answer» C. \[\frac{\lambda }{2\sqrt{2}\pi {{\varepsilon }_{0}}a}\left( \hat{i}+\hat{j}+\hat{k} \right)\]

Discussion

12388.	If a charge q is placed at the center of the line joining two equal charges Q such that the system is in equilibrium then the value of q is
A.	Q/2
B.	#NAME?
C.	Q/4
D.	-Q/4
Answer» E.

Discussion

12389.	A pendulum bob of mass m carrying a charge q is at rest with its string making and angle \[\theta \] with the vertical in a uniform horizontal electric field E. The tension in the string is
A.	\[\frac{mg}{\sin \theta }\text{ and }\frac{qE}{\cos \theta }\]
B.	\[\frac{mg}{\cos \theta }\text{ and }\frac{qE}{\sin \theta }\]
C.	\[\frac{mg}{\cos \theta }\text{ and }\frac{qE}{\sin \theta }\]
D.	\[\frac{mg}{qE}\]
Answer» C. \[\frac{mg}{\cos \theta }\text{ and }\frac{qE}{\sin \theta }\]

Discussion

12390.	Two point dipoles of dipole moment \[{{\vec{p}}_{1}}\]and \[{{\vec{p}}_{2}}\]are at a distance x from each other and \[{{\vec{p}}_{1}}\|\|{{\vec{p}}_{2}}.\] The force between the dipoles is:
A.	\[\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{4{{p}_{1}}{{p}_{2}}}{{{x}^{4}}}\]
B.	\[\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{3{{p}_{1}}{{p}_{2}}}{{{x}^{4}}}\]
C.	\[\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{6{{p}_{1}}{{p}_{2}}}{{{x}^{4}}}\]
D.	\[\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{8{{p}_{1}}{{p}_{2}}}{{{x}^{4}}}\,\]
Answer» C. \[\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{6{{p}_{1}}{{p}_{2}}}{{{x}^{4}}}\]

Discussion

12391.	The electric intensity due to a dipole of length 10 cm and having a charge of \[500\mu C\], at a point on the axis at a distance 20 cm from one of the charges in air, is
A.	\[6.25\times {{10}^{7}}N/C\]
B.	\[9.28\times {{10}^{7}}N/C\]
C.	\[13.1\times {{10}^{11}}N/C\]
D.	\[20.5\times {{10}^{7}}N/C\]
Answer» B. \[9.28\times {{10}^{7}}N/C\]

Discussion

12392.	If \[{{E}_{q}}\] be the electric field strength of a short dipole at a point on its axial line and \[{{E}_{e}}\]that on the equatorial line at the same distance, the n
A.	\[{{E}_{e}}=2{{E}_{a}}\]
B.	\[{{E}_{a}}=2{{E}_{e}}\]
C.	\[{{E}_{a}}={{E}_{e}}\]
D.	None of these
Answer» C. \[{{E}_{a}}={{E}_{e}}\]

Discussion

12393.	In fig., two equal positive point charges \[{{q}_{1}}={{q}_{2}}=2.0\mu C\] interact with a third point charge \[Q=4.0\mu C\]. The magnitude, as well as direction, of the net force on Q is
A.	0.23 N in the +x-direction
B.	0.46 N in the +x-direction
C.	0.23 N in the +x-direction
D.	0.46 N in the +x-direction
Answer» C. 0.23 N in the +x-direction

Discussion

12394.	A uniformly charged and infinitely long line having a liner charge density \[\lambda \] is placed at a normal distance \[y\] from a point O. Consider a sphere of radius \[R\] with O as the center and \[R\] > \[y\]. Electric flux through the surface of the sphere is
A.	Zero
B.	\[\frac{2\lambda R}{{{\varepsilon }_{0}}}\]
C.	\[\frac{2\lambda \sqrt{{{R}^{2}}-{{y}^{2}}}}{{{\varepsilon }_{0}}}\]
D.	\[\frac{\lambda \sqrt{{{R}^{2}}+{{y}^{2}}}}{{{\varepsilon }_{0}}}\]
Answer» D. \[\frac{\lambda \sqrt{{{R}^{2}}+{{y}^{2}}}}{{{\varepsilon }_{0}}}\]

Discussion

12395.	An uncharged aluminum block has a cavity within it. The block is placed in a region where a uniform electric field is directed upward. Which of the following is a correct statement describing conditions in the interior of the block's cavity?
A.	The electric field in the cavity is directed upward.
B.	The electric field in the cavity is directed downward.
C.	There is no electric field in the cavity.
D.	The electric field in the cavity is of varying magnitude and is zero at the exact center.
Answer» D. The electric field in the cavity is of varying magnitude and is zero at the exact center.

Discussion

12396.	The capacitance (in F) of a spherical conductor of radius 1 m is
A.	\[1.1\times {{10}^{-10}}\]
B.	\[{{10}^{-6}}\]
C.	\[9\times {{10}^{-9}}\]
D.	\[{{10}^{-3}}\]
Answer» B. \[{{10}^{-6}}\]

Discussion

12397.	For section AB of a circuit shown in figure,\[{{C}_{1}}=1\mu F\], \[{{C}_{2}}=2\mu F\], \[E=10V\], and the potential difference \[{{V}_{A}}-{{V}_{B}}=10V\]. Charge on capacitor \[{{C}_{1}}\] is
A.	\[0\mu C\]
B.	\[20/3\mu C\]
C.	\[40/3\mu C\]
D.	None of these
Answer» D. None of these

Discussion

12398.	The capacities and connection of. five capacitors are shown in the adjoining figure. The potential difference between the points A and B is 60 volts. Then the equivalent capacity between A and B and the charge on \[5\mu F\] capacitance will be respectively
A.	\[44\mu F;\,\,300\mu C\]
B.	\[16\mu F;\,\,150\mu C\]
C.	\[15\mu F;\,\,200\mu C\]
D.	\[4\mu F;\,\,50\mu C\]
Answer» E.

Discussion

12399.	The equivalent capacitance of three capacitors of Capacitance \[{{C}_{1}}:{{C}_{2}}\] and \[{{C}_{3}}\]are connected in parallel is 12 units and product\[{{C}_{1}}.{{C}_{2}}.{{C}_{3}}=48\]. When the capacitors \[{{C}_{1}}\] and \[{{C}_{2}}\] are connected in parallel, the equivalent capacitance is 6 units. Then the capacitance are
A.	2, 3, 7
B.	1.5, 2.5, 8
C.	1, 5, 6
D.	4, 2, 6
Answer» E.

Discussion

12400.	The electric intensity due to an infinite cylinder of radius and having charge q per unit length at a distance from its axis is [MP PMT 1993; AFMC 2000]
A.	Directly proportional to
B.	Directly proportional to
C.	Inversely proportional to r
D.	Inversely proportional to
Answer» D. Inversely proportional to

Discussion

Explore topic-wise MCQs in Joint Entrance Exam - Main (JEE Main).

Two solids A and B float in water. It is observed that A floats with \[\frac{1}{2}\] of its body immersed in water and B floats with \[\frac{1}{4}\] of its volume above the water level. The ratio of the density of A to that of B is

A hollow sphere of volume V is floating on water surface with half immersed in it. What should be the minimum volume of water poured inside the sphere so that the sphere now sinks into the water

Pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel. This law was first formulated by

An object of weight \[W\] and density\[\rho \] is dipped in a fluid of density \[{{\rho }_{1}}\]. Its apparent weight will be

A metallic block weighs 15 N in air. It weighs 12 N when immersed in water and 13 N when immersed in another liquid. What is the specific gravity of the liquid?

Assertion : The water rises higher in a capillary tube of small diameter than in the capillary tube of large diameter. Reason : Height through which liquid rises in a capillary tube is inversely proportional to the diameter of the capillary tube.

A square plate of 0.1 m side moves parallel to a second plate with a velocity of 0.1 m/s, both plates being immersed in water. If the viscous force is 0.002 N and the coefficient of viscosity is 0.01 poise, distance between the plates in m is [EAMCET (Med.) 2003]

When a body falls in air, the resistance of air depends to a great extent on the shape of the body, 3 different shapes are given. Identify the combination of air resistances which truly represents the physical situation. (The cross sectional areas are the same). [KCET 2005]

In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of \[2.0\text{ }\times \text{ }{{10}^{10}}\] Hz and amplitude \[48\,V\,{{m}^{-1}}\]. Then

An EM wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure p on it. Which of the following is wrong?

The charge on a parallel plate capacitor varies as \[q={{q}_{0}}\,\cos \,2\pi vt\]. The plates are very large and close together (area = A, separation = d). Neglecting the edge effects, the displacement current through the capacitor is

The ratio of contributions made by the electric field and magnetic field components to the intensity of an EM wave is

The rms value of the electric field of the light coming from the Sun is\[720\text{ }N/C\]. The average total energy density of the electromagnetic wave is

Given below is a list of electromagnetic spectrum and its mode of production. Which one does not match?

The waves which are electromagnetic in nature are

A plane electromagnetic wave is incident on a plane surface of area A, normally and is perfectly reflected. If energy E strikes the surface in time t then force exerted on the surface is (c =speed of light)

In an apparatus, the electric field was found to oscillate with an amplitude of\[18\text{ }V/m\]. The magnitude of the oscillating magnetic field will be

If c is the speed of electromagnetic waves in vacuum, its speed in a medium of dielectric constant K and relative permeability \[{{\mu }_{r}}\] is

If \[{{\varepsilon }_{0}}\] and \[{{\mu }_{0}}\] are the electric permittivity and magnetic permeability in vacuum, \[\varepsilon \] and \[\mu \] are corresponding quantities in medium, then refractive index of the medium is

The magnetic field in the plane electromagnetic field is given by: \[{{B}_{y}}=2\times {{10}^{-7}}\sin (0.5\times {{10}^{3}}z+1.5\times {{10}^{11}}t)T\] The expression for the electric field may be given by

The rms value of the electric field of the light coming from sun is 720 N/C. The average energy density of the emf is

The work function of a metallic surface is 5.01 eV. The photoelectrons are emitted when light of wavelength 2000 \[\overset{\text{o}}{\mathop{\text{A}}}\,\] falls on it. The potential difference applied to stop! The fastest photoelectrons is \[\left[ h=4.14\times {{10}^{-15}}eVs \right]\]

A parallel plate capacitor with plate area A and separation between the plates J, is charged by a constant current i. Consider a plane surface of area all parallel to the plates and drawn simultaneously between the plates. The displacement current through this area is

In the circuit shown, the effective capacitano between points X and Y is

A parallel plate capacitor with air between the plates is charged to a potential difference of 500 V and then insulated. A plastic plate is inserted between the plates filling the whole gap. The potential difference between the plates now becomes 75V. The dielectric constant of plastic is

The resultant capacity of n condensers of capacitances \[{{C}_{1}},{{C}_{2}}\ldots .{{C}_{n}}\]connected in parallel is

When air in a capacitor is replaced by medium of dielectric constant K, the capacity

A hollow metal sphere of radius 5 cm is charged such that the potential on its surface is 10 V. The potential at a distance of 2 cm from the center of the sphere is

An electric dipole is put in north-south direction in a sphere filled with water. Which statement is correct?

A surface has the area vector \[\vec{A}=\left( 2\hat{i}+3\hat{j} \right){{m}^{2}}.\] The flux of an electric field through it if the field is \[\vec{E}=4\hat{i}\frac{V}{m}:\]

A sphere of radius R carries charge density \[\rho \]proportional to the square of the distance from the center such that \[\rho =C{{R}^{2}}\], where C is a positive constant. At a distance R/2 from the center, the magnitude of the electric field is

The total electric flux emanating from a closed surface enclosing an \[\alpha -\]particle is (e-electronic charge)

A solid sphere of radius R has a charge Q distributed in its volume with a charge density\[\rho =k{{r}^{a}}\], where k and an are constants and r is the distance from its center. If the electric field at \[r=\frac{R}{2}\] is \[\frac{1}{8}\] times that at \[r=R\], the value of a is.

Three identical positive charges Q are arranged of the triangle is a. Find the intensity of the field at the vertex of a regular tetrahedron of which the triangle is the base.

Find the electric field vector at P (a, a, a) due to three infinitely long lines of charges along the x, y and z- axes, respectively. The charge density, i.e., charge per unit length of each wire is \[\lambda .\]

If a charge q is placed at the center of the line joining two equal charges Q such that the system is in equilibrium then the value of q is

A pendulum bob of mass m carrying a charge q is at rest with its string making and angle \[\theta \] with the vertical in a uniform horizontal electric field E. The tension in the string is

Two point dipoles of dipole moment \[{{\vec{p}}_{1}}\]and \[{{\vec{p}}_{2}}\]are at a distance x from each other and \[{{\vec{p}}_{1}}||{{\vec{p}}_{2}}.\] The force between the dipoles is:

The electric intensity due to a dipole of length 10 cm and having a charge of \[500\mu C\], at a point on the axis at a distance 20 cm from one of the charges in air, is

If \[{{E}_{q}}\] be the electric field strength of a short dipole at a point on its axial line and \[{{E}_{e}}\]that on the equatorial line at the same distance, the n

In fig., two equal positive point charges \[{{q}_{1}}={{q}_{2}}=2.0\mu C\] interact with a third point charge \[Q=4.0\mu C\]. The magnitude, as well as direction, of the net force on Q is

A uniformly charged and infinitely long line having a liner charge density \[\lambda \] is placed at a normal distance \[y\] from a point O. Consider a sphere of radius \[R\] with O as the center and \[R\] > \[y\]. Electric flux through the surface of the sphere is

An uncharged aluminum block has a cavity within it. The block is placed in a region where a uniform electric field is directed upward. Which of the following is a correct statement describing conditions in the interior of the block's cavity?

The capacitance (in F) of a spherical conductor of radius 1 m is

For section AB of a circuit shown in figure,\[{{C}_{1}}=1\mu F\], \[{{C}_{2}}=2\mu F\], \[E=10V\], and the potential difference \[{{V}_{A}}-{{V}_{B}}=10V\]. Charge on capacitor \[{{C}_{1}}\] is

The capacities and connection of. five capacitors are shown in the adjoining figure. The potential difference between the points A and B is 60 volts. Then the equivalent capacity between A and B and the charge on \[5\mu F\] capacitance will be respectively

The electric intensity due to an infinite cylinder of radius and having charge q per unit length at a distance from its axis is [MP PMT 1993; AFMC 2000]