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Recent questions in Class12
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JEEMAIN and NEET
>>
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 is/are false?
jeemain
physics
communication-systems
ch15
class12
easy
basics
asked
Mar 14, 2014
by
sreemathi.v
1
answer
In amplitude modulation,the band width is
jeemain
physics
communication-systems
ch15
class12
easy
basics
asked
Mar 14, 2014
by
sreemathi.v
1
answer
The main purpose of modulation is to
jeemain
physics
communication-systems
ch15
class12
easy
basics
asked
Mar 14, 2014
by
sreemathi.v
2
answers
A bulb connected to 50 V, DC consumes 20 W power. Then the bulb is connected to a capacitor in an a.c. power supply of 250 V, 50 Hz. Find the value of the capacitor required so that the bulb draws the same amount of current.
jeemain
physics
alternating-current
cbse
class12
ch7
ac-voltage-applied-to-capacitor
easy
asked
Mar 12, 2014
by
balaji.thirumalai
1
answer
Calculate the mutual inductance between two coils when a current of 4 A changing to 8 A in 0.5 s in one coil, induces an emf of 50 mV in the other coil.
jeemain
physics
class12
ch6
easy
electromagnetic-induction
inductance
asked
Mar 12, 2014
by
balaji.thirumalai
1
answer
Consider a solenoid coil with $N= 10$ turns with radius $12 \times 10^{−2}m$. The solenoid is subjected to a varying magnetic field that changes uniformly from $5 T \rightarrow 2 T$ in an interval of $12 s$. The axis of the solenoid makes an angle of $13 ^{\circ}$ to the magnetic field. If the angle is changed to $67 ^{\circ}$, what would the radius need to be for the emf to remain the same?
jeemain
physics
cbse
class12
ch6
medium
electromagnetic-induction
faradays-law
asked
Mar 12, 2014
by
balaji.thirumalai
1
answer
A circular coil of $N=5$ turns with radius $r=1.73 m$ is subjected to a varying magnetic field that changes uniformly from $2.18 T$ to $12.7 T$ in an interval of $180 \text{seconds}$. The axis of the solenoid makes an angle of $27 ^{\circ}$ to the magnetic field. Find the induced emf.
jeemain
physics
cbse
class12
ch6
electromagnetic-induction
faradays-law
easy
asked
Mar 12, 2014
by
balaji.thirumalai
1
answer
An aircraft having a wingspan of $20.48\; m$ flies due north at aspeed of $40 ms^{−1}$. If the vertical component of earth’s magneticfield at the place is $2 × 10^{−5}\; T$, Calculate the emf induced betweenthe ends of the wings.
jeemain
physics
tnstate
class12
ch4
easy
electromagnetic-induction
motional-electromotive-force
asked
Mar 12, 2014
by
balaji.thirumalai
1
answer
A circular coil of area $0.04 m^2$, 200 turns and resistance 2 $\Omega$ changes from $0.1 \;Wb \;m^{−2}$ to $0.04 \;Wb\; m^{−2}$ in $0.02 \text{seconds}$. Find the induced emf.
jeemain
physics
cbse
class12
ch6
easy
electromagnetic-induction
faradays-law
asked
Mar 12, 2014
by
balaji.thirumalai
1
answer
Ram is pedaling his bicylce down a road, perpendicular to the Earth's magnetic field of $5.5 \times 10^{-5} T$. His Wheel has an area of $1.2 m^2$. What is the flux through the metal rim of his bicycle wheel?
jeemain
physics
electromagnetic-induction
cbse
class12
ch6
easy
ac-generator
asked
Mar 12, 2014
by
balaji.thirumalai
1
answer
A proton is bombarded on a stationary lithium nucleus. As a result of collision two $\;\alpha\;$ particles are produced . If direction of motion of $\;\alpha \;$ particle with initial direction of motion makes an angle $\;cos^{-1}(\large\frac{1}{4})\;$ find kinetic energy of striking proton . Given binding energies per nucleon of $\;Li^{7}\;$ & $\;He^{4}\;$ are $5.60 MeV$ and $7.06 MeV$ respectively
jeemain
physics
class12
atoms-and-nuclei
difficult
asked
Mar 11, 2014
by
yamini.v
1
answer
The half life of $\;^{215}At\;$ is $\;200 \mu s\;$ . The time taken for radioactivity of a sample of $\;^{215}At\;$ to decay to $\;{\large\frac{1}{4}}^{th}\;$ of its initial value is
jeemain
physics
class11
ch13
nuclei
nuclear-physics
easy
radioactivity
half-life
alpha-beta-and-gamma-decay
asked
Mar 11, 2014
by
yamini.v
1
answer
Ram pedals a stationary bicycle whose pedals are attached to a 1000 turn coil of area 0.10 $m^2$. The coil rotates at half a revolution per second and it is placed in a uniform magnetic field of 0.01 T perpendicular to the axis of rotation of the coil. What is the maximum voltage generated in the coil?
jeemain
physics
electromagnetic-induction
cbse
class12
ch6
easy
ac-generator
asked
Mar 10, 2014
by
balaji.thirumalai
1
answer
A wheel with 10 metallic spokes each 0.3 m long is rotated with a speed of 120 rev/min in a plane normal to the horizontal component of earth’s magnetic field $H_E$ at a place. If $H_E$ = 0.4 G at the place, what is the induced emf between the axle and the rim of the wheel? Note that 1 G = $10^{–4}$ T.
cl31011
jeemain
physics
electromagnetic-induction
cbse
class12
ch6
easy
motional-electromotive-force
asked
Mar 10, 2014
by
balaji.thirumalai
1
answer
A wheel with 10 metallic spokes each 0.5 m long is rotated with a speed of 120 rev/min in a plane normal to the horizontal component of earth’s magnetic field $H_E$ at a place. If $H_E$ = 0.4 G at the place, what is the induced emf between the axle and the rim of the wheel? Note that 1 G = $10^{–4}$ T.
jeemain
physics
motional-electromotive-force
electromagnetic-induction
cbse
class12
ch6
easy
asked
Mar 10, 2014
by
balaji.thirumalai
1
answer
A metallic rod of 1 m length is rotated with a frequency of 100 rev/s, with one end hinged at the centre and the other end at the circumference of a circular metallic ring of radius 1 m, about an axis passing through the centre and perpendicular to the plane of the ring (see fig). A constant and uniform magnetic field of 1 T parallel to the axis is present everywhere. What is the emf between the centre and the metallic ring?
cl31007
jeemain
physics
motional-electromotive-force
electromagnetic-induction
cbse
class12
ch6
medium
asked
Mar 10, 2014
by
balaji.thirumalai
1
answer
A metallic rod of 1 m length is rotated with a frequency of 50 rev/s, with one end hinged at the centre and the other end at the circumference of a circular metallic ring of radius 1 m, about an axis passing through the centre and perpendicular to the plane of the ring (see fig). A constant and uniform magnetic field of 1 T parallel to the axis is present everywhere. What is the emf between the centre and the metallic ring?
jeemain
physics
electromagnetic-induction
cbse
class12
ch6
medium
motional-electromotive-force
asked
Mar 10, 2014
by
balaji.thirumalai
1
answer
A circular coil of radius $10\; cm, 500$ turns and resistance $2 \;\Omega$ is placed with its plane perpendicular to the horizontal component of the earth’s magnetic field. It is rotated about its vertical diameter through $180^{\circ}$ in $0.25\; s$. Estimate the magnitudes of the emf and current induced in the coil. Horizontal component of the earth’s magnetic field at the place is $3.0 × 10^{–5}$ T.
jeemain
physics
electromagnetic-induction
cbse
class12
ch6
easy
faradays-law
asked
Mar 10, 2014
by
balaji.thirumalai
1
answer
A square loop of side 10 cm and resistance 0.5 $\Omega $ is placed vertically in the east-west plane. A uniform magnetic field of 0.10 T is set up across the plane in the north-east direction. The magnetic field is decreased to zero in 0.70 s at a steady rate. Determine the magnitudes of induced emf $\varepsilon$ and current $I$ during this time-interval.
jeemain
physics
electromagnetic-induction
cbse
class12
ch6
medium
faradays-law
asked
Mar 10, 2014
by
balaji.thirumalai
1
answer
The fast neutrons can easily be slowed down by :
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Mar 6, 2014
by
yamini.v
1
answer
Consider $\;\alpha\;, \beta \;, \gamma\;$ rays each having an energy 1 MeV . Arrange them in increasing order of penetrating powers of radiation.
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Mar 6, 2014
by
yamini.v
1
answer
A Beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted from an atomic nucleus. During a negative beta decay $\beta^{-}$, which of the following happens?
jeemain
physics
class11
ch13
nuclei
nuclear-physics
radioactivity
alpha-beta-and-gamma-decay
easy
asked
Mar 6, 2014
by
yamini.v
1
answer
The binding energy per nucleon of deuteron $\;(_{1}^{2}H)\;$ and helium nucleus $\;(_{2}^{4}He)\;$ is 1.1 MeV and 7 MeV respectively . If two deuteron nuclei react to form a single helium nucleus, the energy released is
jeemain
physics
class11
ch13
nuclei
nuclear-physics
nuclear-binding-energy
easy
asked
Mar 6, 2014
by
yamini.v
1
answer
If a nucleus disintegrates i two two nuclear parts which have their velocities in ratio 2 : 1 . The ratio of their nuclear sizes will be .
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Mar 6, 2014
by
yamini.v
1
answer
In a sample of radioactive substance what fraction of initial no . of nuclei will remain undecayed after time $\;t=\large\frac{T}{2}\;$ , where T = half - life of substance
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Mar 6, 2014
by
yamini.v
1
answer
At time zero, there are 10.0 grams of W-187. If the half-life is 23.9 hours, how much will be present at the end of seven days?
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Mar 6, 2014
by
yamini.v
1
answer
In a radioactive process nucleus X finally transforms into a stable nucleus Y . Then X & Y can be :
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Mar 6, 2014
by
yamini.v
1
answer
A radioactive nucleus is being produced at a constant rate x per second . If decay constant is K . If $\;N_{0}\;$ are no . of nuclei at time t=0 , then maximum no . of nuclei possible are :
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Mar 6, 2014
by
yamini.v
1
answer
There are two radioactive substances X & Y . If Decay constant of Y is 2 times of X . Initially both have equal number of nuclei . Then after n half lives of X rate of disintegration of both are equal . The value of n is
jeemain
physics
class12
atoms-and-nuclei
medium
asked
Mar 6, 2014
by
yamini.v
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 no . of atoms decayed between time $\;t_{1}\;$ & $\;t_{2}\;$ are
jeemain
physics
class12
atoms-and-nuclei
easy
asked
Mar 6, 2014
by
yamini.v
1
answer
A sinusoidal electromagnetic plane wave travels through the empty space in $x$ - direction. The electric wave is polarized in the $y$ - direction frequency of waves is $1.5\: GHz$. At a certain point $P$ in space, the oscillating $E_y$ attains a maximum magnitude $E_o = 6.3 \: m V/m$ \[\] The direction of magnetic field vector is along?
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q100
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
A sinusoidal electromagnetic plane wave travels through the empty space in $x$ - direction. The electric wave is polarized in the $y$ - direction frequency of waves is $1.5\: GHz$. At a certain point $P$ in space, the oscillating $E_y$ attains a maximum magnitude $E_o = 6.3 \: V/m$ \[\] The direction of magnetic field vector is along?
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q99
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
A sinusoidal electromagnetic plane wave travels through the empty space in $x$ - direction. The electric wave is polarized in the $y$ - direction frequency of waves is $1.5\: GHz$. At a certain point $P$ in space, the oscillating $E_y$ attains a maximum magnitude $E_o = 6.3 \: mV/m$ \[\] The maximum magnitude $B_o$ of the magnetic field at the point is
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q98
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
A sinusoidal electromagnetic plane wave travels through the empty space in $x$ - direction. The electric wave is polarized in the $y$ - direction frequency of waves is $1.5\: GHz$. At a certain point $P$ in space, the oscillating $E_y$ attains a maximum magnitude $E_o = 6.3 \: V/m$ \[\] What is the wavelength of the wave?
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q97
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
According to electromagnetic wave theory, the electric and magnetic field vector associated with the wave is given by \[\] $|E| = E_{max} \cos(kx – \omega t)$ \[\] $|B| = B_{max} \cos(kx – \omega t)$ \[\] The energy of electromagnetic wave is confined in the form of electric and magnetic fields. The energy per unit volume in an electric field is given by $U_E = \large\frac{1}{2} \in_oE^2$ and the energy per unit volume in a magnetic field is given by $ U_M =\large\frac{1}{2} B^2/ \mu_0$ . The energy density associated with the magnetic field is equal to the energy density associated with the electric field. The total energy is equally shared by the electromagnetic as well as magnetic field. The rate of flow of energy in an electromagnetic wave is defined as pointing vector $S = 1/\mu_o (E \times B)$. A plane electromagnetic wave varies sinusoidally at $90\: MHz $ as it travels along the $+ve\: x$ direction. The peak value of the electric field is $2\: millivolt/m$ and it is directed along $ \pm y$ direction \[\] The average energy density in the radiation is
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q96
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
According to electromagnetic wave theory, the electric and magnetic field vector associated with the wave is given by \[\] $|E| = E_{max} \cos(kx – \omega t)$ \[\] $|B| = B_{max} \cos(kx – \omega t)$ \[\] The energy of electromagnetic wave is confined in the form of electric and magnetic fields. The energy per unit volume in an electric field is given by $U_E = \large\frac{1}{2} \in_oE^2$ and the energy per unit volume in a magnetic field is given by $ U_M =\large\frac{1}{2} B^2/ \mu_0$ . The energy density associated with the magnetic field is equal to the energy density associated with the electric field. The total energy is equally shared by the electromagnetic as well as magnetic field. The rate of flow of energy in an electromagnetic wave is defined as pointing vector $S = 1/\mu_o (E \times B)$. A plane electromagnetic wave varies sinusoidally at $90\: MHz $ as it travels along the $+ve\: x$ direction. The peak value of the electric field is $2\: millivolt/m$ and it is directed along $ \pm y$ direction \[\] The magnetic field vector as a function of time$(t)$ and space$(x)$ is
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q95
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
According to electromagnetic wave theory, the electric and magnetic field vector associated with the wave is given by \[\] $|E| = E_{max} \cos(kx – \omega t)$ \[\] $|B| = B_{max} \cos(kx – \omega t)$ \[\] The energy of electromagnetic wave is confined in the form of electric and magnetic fields. The energy per unit volume in an electric field is given by $U_E = \large\frac{1}{2} \in_oE^2$ and the energy per unit volume in a magnetic field is given by $ U_M =\large\frac{1}{2} B^2/ \mu_0$ . The energy density associated with the magnetic field is equal to the energy density associated with the electric field. The total energy is equally shared by the electromagnetic as well as magnetic field. The rate of flow of energy in an electromagnetic wave is defined as pointing vector $S = 1/\mu_o (E \times B)$. A plane electromagnetic wave varies sinusoidally at $90\: MHz $ as it travels along the $+ve\: x$ direction. The peak value of the electric field is $2\: millivolt/m$ and it is directed along $ \pm y$ direction \[\] The wavelength and period of the wave is respectively
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q94
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
S1: The ground waves can bend round the corners of the objects on earth. \[\] S2: The ground wave propagation can be used for very large distance propagation.
jeemain
aipmt
physics
cbse
class12
ch15
communication-systems
bandwidth-of-signals-and-transmission-medium
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
S1: Radio waves can be polarized. \[\] S2: Sound waves in air are longitudinal in nature.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q92
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
S1: Shielding is required around high energy particle accelerators and high voltage power supplies in T.V. sets \[\] S2: Every accelerated charge particles radiate electromagnetic radiations
jeemain
aipmt
physics
cbse
class12
ch15
communication-systems
bandwidth-of-signals-and-transmission-medium
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
S1: Electromagnetic waves with frequencies more than the critical frequency of ionosphere cannot be used for communication using sky wave communication. \[\] S2: The refractive index of ionosphere becomes very high for frequencies higher than the critical frequency.
jeemain
aipmt
physics
cbse
class12
ch15
communication-systems
bandwidth-of-signals-and-transmission-mediumdifficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
Calculate the magnetic field between the plates at a point $15\: cm$ from the axis.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
displacement-current
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
A $30\: pF$ capacitor has circular plates of area $100\: cm^2$. It is charged by a $70\: V$ battery through a $2\Omega$ resistor. At the instant, the battery is disconnected; the electric field between the plates is changing most rapidly. At this instant, find the rate of change of electric field between the plates.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
displacement-current
difficult
asked
Mar 5, 2014
by
thanvigandhi_1
1
answer
A parallel plate capacitor as shown in the figure is made of circular plates each of radius $R = 6\: cm$, and it has a capacitance $C = 100\: pF$. The capacitor is connected to a $230\: V$ ac supply with a frequency of 300 rad/s. The amplitude $B$ at a point $3\: cm$ from the axis between the plates is
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q87
difficult
asked
Mar 4, 2014
by
thanvigandhi_1
1
answer
Figure shows a capacitor made of two circular plates each of radius $12\: cm$, and separated by $5\: cm$. The capacitor is being charged by an external source. The charging current is constant and equal to $0.15\: A$. The rate of change in potential difference between the plates is
jeemain
aipmt
physics
cbse
class12
ch2
electrostatic-potential-and-capacitance
capacitors-and-capacitance
difficult
asked
Mar 4, 2014
by
thanvigandhi_1
1
answer
Calculate the electric field produced by the radiation coming from a $100\: W$ bulb at a distance of $3\: m$. Assume that the efficiency of the bulb is $2.5\ %$ and it is a point source.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
displacement-current
difficult
asked
Mar 4, 2014
by
thanvigandhi_1
1
answer
A parallel plate capacitor with circular plates of radius $1\: m$ has a capacitance of $1\: nF$. At $t = 0$, it is connected for charging in series with a resistor $R= 1\: M\omega$ across a $2V$ battery. Calculate the magnetic field at a point $ P$, halfway between the centre and the periphery of the plates, after $t = 10–3s$. (The charge on the capacitor at time $t$ is $q (t) = CV [1 – exp (–t/\tau)]$, where the time constant $\tau$ is equal to $CR$.)
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
displacement-current
difficult
asked
Mar 4, 2014
by
thanvigandhi_1
1
answer
Electromagnetic waves travel in a medium at a speed of $2 \times 10^8 m/s$. The relative permeability of the medium is $1$. Calculate the relative permittivity.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
q83
difficult
asked
Mar 4, 2014
by
thanvigandhi_1
1
answer
A parallel plate capacitor with rectangular plates is being discharged. Consider a rectangular loop centered on the plates and between them. The loop measures a by $2a$, the plate measures $2a$ by $4a$. What fraction of the displacement current (i) is encircled by the loop?
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
displacement-current
difficult
asked
Mar 4, 2014
by
thanvigandhi_1
1
answer
A parallel plate capacitor with plate area $A$ and separation $d$ between the plates is charged by a constant current $i$. Consider a plane surface of area $ \large\frac{A}{2}$ parallel to the plates and drawn symmetrically between the plates. Find the displacement current through this area.
jeemain
aipmt
physics
cbse
class12
ch8
electromagnetic-waves
displacement-current
difficult
asked
Mar 4, 2014
by
thanvigandhi_1
1
answer
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