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Recent questions in Class12
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JEEMAIN and NEET
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Physics
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Class12
Class12
Electric Charges and Fields
Electrostatic Potential and Capacitance
Current Electricity
Moving Charges and Magentism
Magnetism and Matter
Electromagnetic Induction
Alternating Current
Electromagnetic Waves
Ray Optics and Optical Instruments
Wave Optics
Dual Nature of Matter and Radiation
Atoms
Nucleii
Semiconductor Materials and Electronic Devices
Communication Systems
Experimental Skills in Physics
Which of the following statements is correct in relation to electromagnetic waves in an isotropic medium? <br> <br> (a) Energy due to electric field is equal to that due to magnetic field. <br> (b) Electric vector E and, magnetic vector B are in phase. <br> (c) For a given amplitude of E vector, the intensity increases as the first power of frequency f <br> (d) For cylindrical wave fronts, the amplitude of the wave varies in proportion to $ \large\frac{1}{r^2}$ , where $r$ is the radius of the wave front.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q80
difficult
asked
Mar 4, 2014
by
thanvigandhi_1
1
answer
S1: In an electromagnetic wave, the average energy density of electric field is equal to the average energy density of the magnetic field \[\] S2: Electric and magnetic fields are related as $E = cB$
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q79
difficult
asked
Mar 3, 2014
by
thanvigandhi_1
1
answer
If an electron and a proton having same momentums enter perpendicularly to a magnetic field, then
jeemain
aipmt
physics
cbse
class12
ch4
moving-charge-and-magnetism
motion-in-combined-electric-and-magentic-fields
difficult
asked
Mar 3, 2014
by
thanvigandhi_1
1
answer
The $rms$ value of the electric field of the light coming from the sun is $720\: N/C$. The average total energy density of the electromagnetic wave is
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q77
difficult
asked
Mar 3, 2014
by
thanvigandhi_1
1
answer
Given below are some famous numbers associated with electromagnetic radiations in different contexts in physics. Which of the following belongs to radio waves?
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q76
difficult
asked
Mar 3, 2014
by
thanvigandhi_1
1
answer
S1: Magnetic flux is vector quantity. \[\] S2: Value of magnetic flux can be positive, negative or zero.
jeemain
aipmt
physics
cbse
class12
ch6
electromagnetic-induction
magnetic-flux
difficult
asked
Mar 3, 2014
by
thanvigandhi_1
1
answer
The variation of current versus time is \[\] The potential difference across a 2H inductor as function of time is shown in figure. At time $t=0$, current is zero.
jeemain
aipmt
physics
cbse
class12
ch6
electromagnetic-induction
inductance
difficult
asked
Mar 3, 2014
by
thanvigandhi_1
1
answer
Current at $t = 1 \: s$ is
jeemain
aipmt
physics
cbse
class12
ch6
electromagnetic-induction
inductance
difficult
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
Area under $V_L - t$ graph gives
jeemain
aipmt
physics
cbse
class12
ch5
electromagnetic-induction
inductance
difficult
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
Magnitude of induced emf produced in a coil when a magnet is inserted into it depends on the
jeemain
aipmt
physics
cbse
class12
ch5
electromagnetic-induction
faradays-law
difficult
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
Calculate the energy of electromagnetic waves of wavelength $3000\: A^{\circ}.$
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q70
medium
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
A plane electromagnetic wave in the visible region is moving along the $z$ direction. The frequency of the wave is $0.5 \times 10^{15}Hz$ and the electric field at any point is varying sinusoidally with time with amplitude of $1\: V/m$. Calculate the average values of densities of the magnetic field.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q69
medium
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
Find the average energy stored in a 60 cm length of a laser beam operating at $4\: mW.$
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q68
medium
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
Find the amplitude of the electric field in a parallel beam of light of intensity $2\: W/m^2$
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q67
medium
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
The electric field in an electromagnetic wave is given by $E = 50N/C\: \sin \omega (t-x/c)$. Find the energy contained in a cylinder of cross-section $10cm^2$ and length 50 cm along the x-axis.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q66
medium
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
The average energy flux of sunlight is $1\: kW/m^2$. This energy is falling normally on the plate surface of area $10\: cm^2$ which completely absorbs the energy. How much force is exerted on the plate if it is exposed to sunlight for 20 minutes?
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q65
medium
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
The magnetic field in a plane electromagnetic wave is given by $B = 100\mu T \sin [(2 \times10^{15}s^{-1}) (t-x/c)]$. Calculate the average energy density corresponding to the electric field.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q64
medium
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
A light beam travelling in the x-direction is described by the electric field $E_y = 300 \: V/m \: \sin \omega\: (t – x/c)$. An electron is constrained to move along the y-direction with a speed of $2 \times 10^7 m/s$. Find the maximum magnetic force on the electron
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q63
medium
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
A plane sinusoidal linearly polarized electromagnetic wave of wavelength $ 5 \times 10^{-7}m$ travels in vacuum in the direction of $x$ - axis. The average intensity of the wave per unit area is $0.1\: W/m^2$ and the plane of vibration of electric field is parallel to $y$ - axis. The equations describing the electric and magnetic field of this wave is
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
medium
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
A $60W$ monochromatic point source radiating equally in all directions in vacuum is being monitored at a distance of $2m$. Determine the amplitude if the electric field.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q61
medium
asked
Mar 1, 2014
by
thanvigandhi_1
1
answer
A laser emits a beam of light of $2mm$ diameter. If the power of beam is $10mW$, the intensity of the beam of light is
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q60
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
We can establish an instantaneous displacement current of $1\: A$ in the space between the two plates of a $1\: \mu\: F$ parallel plate capacitor by varying voltage at the rate of
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
displacement-current
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
A parallel plate capacitor has circular plates, each of radius $5\: cm$. It is being charged so that electric field in the gap between its plates rises steadily at the rate of $10^{12}V/ms$. What is the displacement current?
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
displacement-current
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
A radio wave of intensity $I$ is reflected by a surface. The intensity $ (I)$, if pressure exerted on the surface is $2 \times 10^{-8} N/m^2$ , will be:
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
What is order of energy of X-rays $(E_X)$, radio waves $(E_R)$, and micro waves $(E_M)$?
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
electromagnetic-specturm
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
A TV tower has a height of $100\: m$. The area covered by the TV broadcast, if radius of the earth is $6400\: km$, will be:
jeemain
aipmt
physics
cbse
class12
ch15
communication-systems
bandwidth-of-signals-and-transmission-medium
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
Some radio waves of frequency of about $1.5 \times 10^9$ Hz were received by a radio-telescope from distant star. If the speed of the waves is $3 \times 10^5 \: km/s$, then the wave- length of the wave will be:
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
electromagnetic-spectrum
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
An object is placed at some distance from a radio station. If the interval between transmission and reception of pulses is $2.66 \times 10^{-2}\: sec$, then the distance is:
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
electromagnetic-spectrum
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
The speed of light in air, if an electromagnetic wave is travelling in air whose dielectric constant is $k = 1.006$, will be :
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q52
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
The energy of photon of electromagnetic radiation of wavelength = $2000\: A^{\circ}$ is:
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
The AM radio wave bends appreciably round the corners of a $1m \times 1m$ board but the FM wave only negligibly bands. If the average wavelength of the AM and FM waves are $ \lambda_a$ and $\lambda_f$ , then
jeemain
aipmt
physics
cbse
class12
ch15
communication-systems
modulation
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
If an electromagnetic wave of frequency $v = 3.0\: MHz$ passes from vacuum into a dielectric medium with permittivity $e = 4.0$ then
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
An uniform electric field and an uniform magnetic field are acting along the same direction in a certain region. If an electron is projected along the direction of the fields with a certain velocity, then
jeemain
aipmt
physics
cbse
class12
ch4
moving-charge-and-magnetism
motion-in-combined-electric-and-magentic-fields
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
In a region, steady and uniform electric and magnetic fields are present. These two fields are parallel to each other. A charged particle is released from rest in this region. The path of the particle will be a
jeemain
aipmt
physics
cbse
class12
ch4
moving-charge-and-magnetism
motion-in-combined-electric-and-magentic-fields
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
If a source of power $4\: kW$ produce $10^{20}$photons/s, the radiation belongs to a part of spectrum called
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
electromagnetic-specturm
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
The time period of a charged simple pendulum in an electric field is:
jeemain
aipmt
physics
cbse
class12
ch1
electric-charges-and-fields
electric-field
medium
asked
Feb 28, 2014
by
thanvigandhi_1
1
answer
If activity of a radioactive substance's $\;A_{1}\;$ at time $\;t_{1}\;$ & $\;A_{2}\;$ at time $\;t_{2}\;$ $\;(> t_{1})\;$ . Its decay constant is $\;\lambda\;$ . Then
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Feb 28, 2014
by
yamini.v
1
answer
If ratio of molecular masses of two radioactive substances is $\;\large\frac{1}{2}\;$ and ratio of decay constant is $\;\large\frac{5}{3}\;$ . Then ratio of their initial activity per mole will be
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Feb 28, 2014
by
yamini.v
1
answer
x atoms of a radioactive element emit y beta particles per second . Then the decay constant of element is (in $\;s^{-1}$) .
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Feb 28, 2014
by
yamini.v
1
answer
The equation : \[\] $\;4 _{1}^{1}H \to _{2}^{4}He^{2+}+2e^{-}+32 MeV\;$ represents
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Feb 28, 2014
by
yamini.v
1
answer
Which of the following is correct statement ?
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Feb 28, 2014
by
yamini.v
1
answer
$\;^{22}Ne\;$ Nucleus after absorbing energy , decays into two $\;\alpha-\;$ particles and an unknown nucleus . The unknown nucleus is
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Feb 28, 2014
by
yamini.v
1
answer
The half -life period of a radioactive element A is same as mean life of another radioactive element B . Initially both of them have same number of atoms
jeemain
physics
class12
atoms-and-nuclei
medium
asked
Feb 28, 2014
by
yamini.v
1
answer
A nucleus with mass number 200 initially at rest emits and $\;\alpha-\;$ particle . If Q value of reaction is 4.2MeV .Then kinetic energy of $\;\alpha-\;$ particle will be
jeemain
physics
class12
atoms-and-nuclei
medium
asked
Feb 28, 2014
by
yamini.v
1
answer
Two radioactive materials A & B have decay constants 12X & X respectively . If initially they have same no.of nuclei , then ratio of no. of nuclei of A to B will be $\;\large\frac{1}{e}\;$ after a time
jeemain
physics
class12
atoms-and-nuclei
medium
asked
Feb 27, 2014
by
yamini.v
1
answer
Half life of a radioactive substance A is 4 days . The probability that a nucleus will decay in two half-lives is :
jeemain
physics
class12
atoms-and-nuclei
medium
asked
Feb 27, 2014
by
yamini.v
1
answer
If a star can convert all He nuclei completely into oxygen nuclei . The energy released per oxygen nuclei is . [Mass of nucleus He is 4.0026 amu & mass of oxygen nucleus is 15.9994]
jeemain
physics
class12
atoms-and-nuclei
medium
asked
Feb 27, 2014
by
yamini.v
1
answer
A star initially has $\;10^{4}\;$ deuterons . It produces energy via the process \[\] $\;_{1}H^{2}+_{1}H^{2} \to _{1}H^{3}+P\;$ and \[\] $\;_{1}H^{2}+_{1}H^{3} \to _{2}He^{4}+n\;$\[\] If average power radiated by star is $\;10^{16} W\;$ the deutron supply of star is exhausted in a time of order of
jeemain
physics
class12
atoms-and-nuclei
medium
asked
Feb 27, 2014
by
yamini.v
1
answer
The binding energy of two nuclei A & B are X & Y . Two atoms of A fuse to give one atom of B an energy P is released . Then
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Feb 27, 2014
by
yamini.v
1
answer
The half life of radioactive radon is 3.8 days . The time , at end of which $\;\large\frac{1}{20}^{th}\;$ of radon sample will remain undecayed is
jeemain
physics
class11
ch13
nuclei
nuclear-physics
radioactivity
half-life
easy
asked
Feb 27, 2014
by
yamini.v
1
answer
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