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CBSE XII
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Physics
Physics
Electric charges and fields
Electrostatic Potential and Capacitance
Current Electricity
Moving charges and magnetism
Magnetism and matter
Electromagnetic induction
Alternating current
Electromagnetic waves
Ray optics and optical instruments
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Dual nature of radiation and matter
Atoms
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In the circuit given below , when the input voltage of the base resistance is $10\;V,V_{BE}$ is zero. and $V_{CE}$ is also zero. Find the value of $I_b$
cbse
class12
physics
ch-14
sec-a
exemplar
easy
asked
Dec 31, 2016
by
meena.p
1
answer
A p-n photo diode is fabricated from a semi - conductor with a band gap of $2.5 \;ev$. It can detect a signal of wavelength
cbse
class12
physics
ch-14
sec-a
additional
medium
asked
Dec 31, 2016
by
meena.p
1
answer
Figure shows a metal rod PQ resting on the smooth rail AB and positioned between the poles of a permanent magnet. The rail, the rod and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = $9.0 m \Omega$. Assume the field to be uniform.
Suppose K is open and the rod is moved with a speed of 12cm/s in the direction shown. Give the polarity and magnitude of the induced $emf$.
cbsc
class-12
physics
electromagnetic-induction
sec-b
ncert
medium
asked
Dec 31, 2016
by
priyanka.c
1
answer
The voltage gain of an amplifier with $9\%$ negative feed back is $10$. The voltage gain with out feedback will be
cbse
class12
physics
ch-14
sec-a
additional
medium
asked
Dec 31, 2016
by
meena.p
1
answer
The decimal equivalent of the binary number $(11010.101)_2$ is
cbse
class12
physics
ch-14
sec-a
additional
medium
asked
Dec 31, 2016
by
meena.p
1
answer
An amplifier has a voltage gain $A_v= 1000$ The voltage gain $dB$ is
cbse
class12
physics
ch-14
sec-a
additional
medium
asked
Dec 31, 2016
by
meena.p
1
answer
In a common emitter transistor amplifier , the output resistance is $500 \;k \Omega$ and the current gain $\beta =49$ . If the power gain of the amplifier is $5 \times 10^6$, the input resistance is
cbse
class12
physics
ch-14
sec-b
additional
medium
asked
Dec 31, 2016
by
meena.p
1
answer
In a transistor $\beta=49$ , then what percentage of charge carriers from emitter reach the collector ?
cbse
class12
physics
ch-14
sec-b
additional
medium
asked
Dec 31, 2016
by
meena.p
1
answer
A semiconductor has equal electron and hole concentration $6 \times 10^8\;m^{-3}$. On doping with a certain impurity , electrons concentration increases to $8 \times 10^{12}m^{-3}$. Identify the type of semiconductor after doping
cbse
class12
physics
ch-14
sec-a
additional
easy
asked
Dec 31, 2016
by
meena.p
1
answer
What is the order of energy gap in a semi-conductor ?
cbse
class12
physics
ch-14
sec-a
additional
easy
asked
Dec 31, 2016
by
meena.p
1
answer
give the ratio of number of numbers holes and number of conduction electrons in an intrinsic semi conductor
cbse
class12
physics
ch-14
sec-a
additional
easy
asked
Dec 31, 2016
by
meena.p
1
answer
It is desired to measure the magnitude of field between the poles of a powerful loud speaker magnet. A small flat search coil of area $2cm^2$ with closely wound turns, is positioned normal to the field direction and then quickly snatched out of the field region. Equivalently one can give it a quick $90^{\circ}$ turns to bring its plane parallel to the field direction. The total change flown in the coil (measured by a ballistic galvanometer connected to coil) is 7.5mc. The combined resistance of the coil and the galvanometer $0.50 \Omega$. Estimate the field strength of magnet.
cbsc
class12
physics
electromagnetic-induction
sec-c
ncert
medium
asked
Dec 30, 2016
by
priyanka.c
1
answer
A square loop of side 12cm with its sides parallel to X and Y axes is moved with a velocity of 8 cm/s in the positive X-direction in an environment containing a magnetic field in the positive Z-direction. The field is neither uniform in space nor constant in time. It has a gradient of $10^{-3}$T/cm along the negative X-direction (that is it increases by $10^{-3}$T/cm as one moves in the negative X-direction) and it is decreasing in time at the rate of $10^{-3} $ T/S. Determine the direction and magnitude of the induced current in the loop if its resistance is $4.50 m\Omega$
cbsc
class12
physics
electromagnetic-induction
sec-c
ncert
difficult
asked
Dec 30, 2016
by
priyanka.c
1
answer
Suppose a rectangular loop of sides 8cm and 2cm with a small cut is stationary but the current feeding the electromagnet that produces the magnetic field is gradually reduced so that the field decreases from its initial value of 0.3T at the rate of 0.02T/S. If the cut is joined and the loop has a resistance of 1.6$ \Omega$, how much power is dissipated by the loop as heat? What is the source of this power ?
cbsc
class12
physics
electromagnetic-induction
sec-c
ncert
difficult
asked
Dec 30, 2016
by
priyanka.c
1
answer
A magnetic field in a certain region is given by $ B = B_0 cm (\omega t) \hat {k}$ and a coil of radius "a" with resistance R is placed in the x - y plane with its centre at the origin in the magnetic field, as shown in the fig. Find the magnitude and th direction of the current at (a, 0, 0) at $ t = \frac {\pi}{2\omega} \; and \; t = \frac {3 \pi}{2 \omega}$
cbse
class 12
physics
chap-6
sec-c
electromagnetic-induction
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
In p-n junction diode , the current I , can be expressed $I= I_0 exp \bigg[ \large\frac{eV}{K_{B}T}-1 \bigg]$ Where $I_0$ is called the satiation current , V is the voltage across the dicode and in positive for forward bias and negative for reverse bias and I is the current through the dicode , $K_B$ is the Boltzmann constant $(8.6 \times 10^{-5}e^v/k)$ and T is the absolute temperature . If for a given diode $I_0 = 5 \times 10^{-12}A $ and $T=300\;K$ , then what will be the increase in the current if the voltage across the diode is increased to $0.7\;A$?
cbse
class12
physics
ch-14
sec-b
ncert
medium
asked
Dec 30, 2016
by
meena.p
1
answer
A rectangular loop of wire ABCD is kept close to an infinitely long wire carrying a current $ I (t) = I_0 (1 - \frac {t}{T}) for $ 0 \leq t \leq T$ and $ I (0) = 0$ for t > T, as shown in the fig. Find the total charge passing through a given point in the loop, in time T, The resistance of the loop is R.
cbse
class 12
physics
chap-6
sec-c
electromagnetic-induction
exemplar
difficult
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
In p-n junction diode , the current I , can be expressed $I= I_0 exp \bigg[ \large\frac{eV}{K_{B}T}-1 \bigg]$ Where $I_0$ is called the satiation current , V is the voltage across the dicode and in positive for forward bias and negative for reverse bias and I is the current through the dicode , $K_B$ is the Boltzmann constant $(8.6 \times 10^{-5}e^v/k)$ and T is the absolute temperature . If for a given diode $I_0 = 5 \times 10^{-12}A $ and $T=300\;K$ , then what will be the forward current at a forward voltage of $0.6\;V$?
cbse
class12
physics
ch-14
sec-b
ncert
difficult
asked
Dec 30, 2016
by
meena.p
1
answer
Consider an infinitely long wire carrying a current I(t), with $ \frac {dI}{dt} = \lambda = constant$. Find the current produced in the rectangular loop of wire ABCD if its resistance is R, as shown in the fig.
cbse
class 12
physics
chap-6
sec-c
electromagnetic-induction
exemplar
difficult
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
In an intrinsic semiconductor the energy gap $E_g$ is $1.2\;ev$ . It hole mobility and independent of temperature . What is the ratio between conductivity at $600\;k$ and $300\;k$ Assume that the temperature dependence intrinic concentration $n_i$ is given by $n_i = n_0 exp\bigg(\large\frac{-Eg}{2K_b t}\bigg)$, Where $n_o$ is a Constant and $K_b= 8.62 \times 10^{-5} ev/K$
cbse
class12
physics
ch-14
sec-b
ncert
difficult
asked
Dec 30, 2016
by
meena.p
1
answer
A magnetic field B is confined to a region $r \leq a$ and points out the paper (the Z axis) $ r = 0$ being the centre of the circular region. A charged ring (charge = Q) of radius b $b>a$ and mass m lies in the xy plane with its centre at the origin. the ring is free to rotate and is at rest. The magnetic field is brought to zero in time $\bigtriangleup t$. Find the angular velocity $\omega$ of the ring after the field vanister.
cbse
class 12
physics
chap-6
sec-c
electromagnetic-induction
exemplar
difficult
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
Give the expression for average value of a.c voltage $V = V_0\; sin \omega t$ over time interval $ t = 0 \; to \; t = \frac {\pi}{\omega}$
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional question
medium
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A jet plane is travelling towards west at a speed of $1800\; km/hr$. What is the voltage difference developed between the ends of the wing having a span of 25m, if the earth's magnetic field at the location has a magnitude of $5 \times 10^{-4} T$ and the dip angle is $30^{\circ}$
cbsc
class12
physics
electromagnetic-induction
sec-c
ncert
difficult
asked
Dec 30, 2016
by
priyanka.c
1
answer
The number of silicon atoms per $m^3$ is $5 \times 10^{28}$ This is doped simultaneously with $ 5 \times 10^{22}$ atom per $m^3$ of and $ 5 \times 10^{26}$ per $m^3 $ atoms of indium . Calculate the number of electrons and holes . Given that $n_i=1.5 \times 10^{16}\;m^{-3}$. material n -type or p type
cbse
class12
physics
ch-14
sec-a
ncert
easy
asked
Dec 30, 2016
by
meena.p
1
answer
An electrical element x connected to an alternating voltage source has current through it leading the voltage by $\frac {\pi}{2}$ radius. Identify x and write an expression for its reactance.
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional question
medium
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A pair of adjacent coils have a mutual inductance of 1.5 H. If the current in one is changed from $0 \; to\; 20 A$ is $0.5 S$ , what is the change of flux with the other coil.
cbsc
class12
physics
electromagnetic-induction
sec-b
ncert
medium
asked
Dec 30, 2016
by
priyanka.c
1
answer
Self induction of an air core inductor increases from 0.01 MH to 10 MH on introducing an iron core into it. What is the relative permeability of the core used?
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional question
medium
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
The dimension of $\frac {h}{e}$ is the same as that of magnetic flux $\phi$. Say true or false.
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional question
easy
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A P-n junction is fabricated from a semiconductor with band gap of $2.8\;ev$ can it detected a wavelength of $600\;nm$?
cbse
class12
physics
ch-14
sec-a
ncert
easy
asked
Dec 30, 2016
by
meena.p
1
answer
The dimensions of electric and magnetic flux are same. Say true or false.
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional question
easy
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A coil of a metal wire is kept stationary in a non - uniform magnetic field. An emf is induced in the coil. Say true or false.
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional question
easy
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a voltage gain of $10$ and the second has a voltage gain of 20. If the input signal is $0.01\;V$ calculate the output a.c signal
cbse
class12
physics
ch-14
sec-a
ncert
medium
asked
Dec 30, 2016
by
meena.p
1
answer
A magnetic field of 10T acts normal to a coil of 50 turns having $100 cm^2$ area. Find emf induced if the coil is removed from magnetic field in 0.1 sec.
cbse
class 12
physics
chap-6
sec-b
electromagnetic-induction
additional quest
medium
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A circular copper disc 10 cm in radius rotates at $20\pi$ rad/s about an axis through its centre and perpendicular to its disc. A uniform magnetic field of 0.2T acts perpendicular to the disc. Calculate the induced current if the resistance of the disc is $2\Omega$.
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional quest
medium
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A circular copper disc 10 cm in radius rotates at $20\pi$ rad/s about an axis through its centre and perpendicular to its disc. A uniform magnetic field of 0.2T acts perpendicular to the disc. Calculate the potential difference developed between the axis of the disc and the rim.
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional quest
medium
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A wheel with 50 metallic spokes each 0.5 m long is rotated with an angular speed of 12 radian /sec, in a plane normal to the earth's magnetic field. If the magnitude of the field is $ 0.5 \times 10^{-4}$ T, calculate the emf induced between the axle and the rim of the wheel.
cbse
class 12
physics
chap-6
sec-b
electromagnetic-induction
additional quest
difficult
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A cylindrical bar magnet is kept along the axis of a circular coil and near it as shown in the fig. Will there be any induced e.m.f at the terminals of the coil, when the magnet is rotated about an axis perpendicular to the length of the magnet?
cbse
class
12
physics
chap-6
sec-a
electromagnetic-induction
additional
quest
easy
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A cylindrical bar magnet is kept along the axis of a circular coil and near it as shown in the fig. Will there be any induced e.m.f at the terminals of the coil, when the magnet is related about its own axis.
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional qust
easy
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A horizontal straight wire $10 \;cm$ long expending from east to west is falling with a speed of $5.0\; m/s $ at right angles to the horizontal component of the earth's magnetic field $0.30 \times 10^{-4}\;wb/m^2$. Which end of the wire is at the higher electrical potential ?
cbsc
class12
physics
electromagnetic-induction
sec-a
ncert
easy
asked
Dec 30, 2016
by
priyanka.c
1
answer
A horizontal straight wire $10 \;cm$ long expending from east to west is falling with a speed of $5.0\; m/s $ at right angles to the horizontal component of the earth's magnetic field $0.30 \times 10^{-4}\;wb/m^2$. What is the direction of the induced $emf$.
cbsc
class12
physics
electromagnetic-induction
sec-a
ncert
easy
asked
Dec 30, 2016
by
priyanka.c
1
answer
For a common emitter amplifier , the audio signal voltage across the collector resistance of $2\;HK \Omega$ is $2V$. Suppose the current amplification factor of a transistor is 100, find the input signal voltage and base current , if the base resistance is $1\;k \;\Omega$
cbse
class12
physics
ch-14
sec-b
ncert
medium
asked
Dec 30, 2016
by
meena.p
1
answer
What is the output frequency of a full wave rectifier if the input frequency is $50\;Hz$
cbse
class12
physics
ch-14
sec-a
ncert
easy
asked
Dec 30, 2016
by
meena.p
1
answer
A circular coil of radius 8.0 cm and 20 turns rotates about its vertical diameter with an angular speed of $ 50 rad s^{-1}$ in a uniform horizontal magnetic field of magnitude $ 3 \times 10^{-2} T$. It the coil forms a closed loop of resistance $ 10 \Omega$, calculate the power dissipated as heat.
cbse
class
12
physics
chap-6
sec-b
electromagnetic-induction
addditional
qust
medium
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
A circular coil of radius 8.0 cm and 20 turns rotates about its vertical diameter with an angular speed of $ 50 rad s^{-1}$ in a uniform horizontal magnetic field of magnitude $ 3 \times 10^{-2} T$. Calculate the average emf.
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional quest
easy
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
In half wave rectifier , what is the output frequency if the input frequency is $50\;Hz$?
cbse
class12
physics
ch-14
sec-a
ncert
easy
asked
Dec 30, 2016
by
meena.p
1
answer
A circular coil of radius 8.0 cm and 20 turns rotates about its vertical diameter with an angular speed of 50 $rad s^{-1}$ in a uniform horizontal magnetic field of magnitude $ 3 \times 10^{-2} T$. Calculate the maximum emf induced in the coil.
cbse
class 12
physics
chap-6
sec-b
electromagnetic-induction
additional quest
medium
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
For tramister amplifier , the voltage gain ,
cbse
class12
physics
ch-14
sec-a
ncert
easy
asked
Dec 30, 2016
by
meena.p
1
answer
Write a expression for mutual inductance of two coaxial solenoids.
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional quest
easy
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
Why are resistance coils usually double wound?
cbse
class 12
physics
chap-6
sec-a
electromagnetic-induction
additional quest
medium
asked
Dec 30, 2016
by
suganyadevi.p
1
answer
For a transistor action, which of the following statements are correct ?
cbse
class12
physics
ch-14
sec-a
ncert
easy
asked
Dec 30, 2016
by
meena.p
1
answer
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