Recent questions tagged 2006

Two spherical conductors A and B of radii 1 mm and 2 mm are separated by distance of 5 cm and are uniformly charged. If the spheres are connected by a conducting wire then in equilibrium conditon, the ratio of the magnitude of the electric fields at the surfaces of spheres A and B is :

asked Nov 13, 2018 by pady_1

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An inductor $(L=100 mH)$, a resistor $(R = 100 \Omega )$ and a battery $(E = 100 V)$ are initially connected in series as shown in the figure. After a long time the battery is disconnected after short circuiting the points A and B. The current in the circuit 1 ms after the short circuit is :

asked Nov 13, 2018 by pady_1

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A wire elongates by $l\; mm$ when a load $W$ is hanged from it. If the wire goes over a pulley and two weights $W $ each are hung at the two ends, the elongation of the wire will be (in mm) :

asked Nov 13, 2018 by pady_1

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A thin circulr ring of mass m and radius R is rotating about its axis with a constant angular velocity $\omega$. Two objects each of mass M are attached gently to the opposite ends of a diameter of the ring. The ring now rotates with an angular velocity $\omega'$.

asked Nov 13, 2018 by pady_1

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The potential energy of a 1 kg particle free to move along the $x$-axis is given by $V(x) = (\frac{x^4}{4} - \frac{x^2}{2} ) J$ The total mechanical energy of the particle is $2J$. Then, the maximum speed (in m/s) is:

asked Nov 13, 2018 by pady_1

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A force of $-F \hat{k}$ acts on O, the origin of the co-ordinate system. The torque about the point $(1, -1)$ is :

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Four point masses, each of value $m$, are placed at the corners of a square ABCD of side $l$. The moment of inertia of this system about an axis passing through A and parallel to BD is :

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A coin is placed on a horizontal platform which undergoes vertical simple harmonic motion of angular frequency $\omega$. The amplitude of oscillation is gradually increased. The coin will leave contact with the platform for the first time:

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The 'rad' is the correct unit used to report the measurement of :

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An electric bulb is rated 220 volt - 100 watt. The power consumed by it when operated on 110 volt will be :

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If the binding energy per nucleon in $_3^7 Li$ and $_2^4 He$ nuclei are 5.60 MeV and 7.06 MeV respectively, then in the reaction : $p + _3^7 Li \to 2 _2^4 He$ energy of proton must be :

asked Nov 13, 2018 by pady_1

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The anode voltage of a photocell is kept fixed. The wavelength $\lambda$ of the light falling on the cathode is gradually changed. The plate current $I$ of the photocell varies as follows :

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In the following, which one of the diodes is reverse biased ?

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The circuit has two oppositely connected ideal diodes in parallel. What is the current flowing in the circuit ?

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A long solenoid has 200 turns per cm and carries a current $i$. The magetic field at its centre is $6.28 \times 10^{-2}weber/m^2$. Another long solenoid has 100 turns per cm and it carries a current $i/3$. The value of the magnetic field at its current is :

asked Nov 13, 2018 by pady_1

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The flux linked with a coil at any instant 't' is given by : $\phi = 10t^2 - 50 t + 250$ The induced emf at $t =3s$ is :

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In a Wheatstone's bridge, three resistances P, Q and R are connected in the three arms and the fourth arm is formed by two resistances $S_1$ and $S_2$ connected in parallel. The condition for the bridge to be balanced will be :

asked Nov 13, 2018 by pady_1

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If the ratio of the concentration of electrons to that of holes in a semiconductor is $\frac{7}{5}$ and the ratio of currents is $\frac{7}{4}$, then what is the ratio of their drift velocities ?

asked Nov 13, 2018 by pady_1

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The refractive index of glass is 1.520 for red light and 1.525 for blue light. Let $D_1$ and $D_2$ be angles of minimum deviation for red and blue light respectively in a prism of this glass, then :

asked Nov 13, 2018 by pady_1

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A solid which is not transparent to visible light and whose conductivity increases with temperature is formed by :

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In an AC generator, a coil with N turns, all of the same area A and total resistance R, rotates with frequency $\omega$ in a magnetic field B. The maximum value of emf generated in the coil is :

asked Nov 13, 2018 by pady_1

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Two insulating plates are both uniformly charged in such a way that the potential difference between them is $V_2 -V_1 = 20 V$.(i.e, plate 2 is at a higher potential). The plates are separated by $d=0.1 \;m$ and can be treated as infinitely large. An electron is released from rest on the inner surface of plate 1. What is its speed when it hits plate 2 ? ($e = 1.6 \times 10^{-19} C, m_0 = 9.11 \times 10^{-31} kg$)

asked Nov 13, 2018 by pady_1

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The resistance of a bulb filament is $100 \Omega$ at a temperature of $100^{\circ}$C. If its temperature coefficient of resistance be $0.005 \; per \; ^{\circ}C$, its resistance will become $200 \Omega$ at a temperature of :

asked Nov 13, 2018 by pady_1

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In a series resonant LCR circuit, the voltage across R is 100 volts and $R = 1\;k \Omega$ with $C = 2 \mu F$. The resonant frequency $\omega$ is 200 rad/s. At resonance the voltage across L is :

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The energy spectrum of $\beta$-particles (number N(E) as a function of $\beta$-energy E] emitted from a radioactive source is :

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The current $I$ drawn from the 5 volt source will be :

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When $_3 Li^7$ nuclei are bombarded by protons, and the resultant nuclei are $_4Be^8$, the emitted particles will be :

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The time taken by a photoelectron to come out after the photon strikes is approximately :

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An alpha nucleus of energy $\frac{1}{2} mv^2$ bombards a heavy nuclear target of charge $Ze$. Then the distance of closest approach for the alpha nucleus will be proportional to :

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The threshold frequeny for a metallic surface corresponds to an energy of 6.2 eV and the stopping potential for a radiation incident on this surface is 5V. The incident radiation lies in :

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A thermocouple is made from two metals, Antimony and Bismuth. If one junction of the couple i kept hot and the other is kept cold, then, an electrix current will :

asked Nov 13, 2018 by pady_1

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In a common-base mode of a transistor, the collector current is 5.488 mA for an emitter current of 5.60 mA. The value of the base current amplification factor ($\beta$) will be:

asked Nov 13, 2018 by pady_1

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A player caught a cricket ball of mass 150 g moving at a rate of 20 m/s. If the catching process is completed in 0.1 s, the force of the blow exerted by the ball on the hand of the player is equal to :

asked Nov 13, 2018 by pady_1

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Consider a two particle system with particles having masses $m_1$ and $m_2$. If the first particle is pushed towards the centre of mass through a distance d, by what distance should the second particle be moved, so as to keep the centre of mass at the same position ?

asked Nov 13, 2018 by pady_1

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A string is stretched between fixed points separated by 75.0 cm. It is observed to have resonant frequencies of 420 Hz and 315 Hz. There are no other resonant frequencies between these two. Then, the lowest resonant frequency for this string is :

asked Nov 13, 2018 by pady_1

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A ball of mass 0.2 kg is thrown verticlly upwards by applying a force by hand. If the hand moves 0.2 m while applying the force and the ball goes upto 2 m height further, find the magnitude of the force, consider $g=10\; m/s^2$ :

asked Nov 13, 2018 by pady_1

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Which of the following units denotes the dimensions $[ML^2/Q^2]$, where $Q$ denotes the electric charge ?

asked Nov 13, 2018 by pady_1

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Assuming the Sun to be a spherical body of radius R at a temperature of T K, evaluate the total radiant power, incident on earth, at a distance r from the Sun : where $r_0$ is the radius of the earth and $\sigma$ is Stefan's constant .

asked Nov 13, 2018 by pady_1

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Starting from the origin a body oscillates simple harmonically with a period of 2 s. After what time will its kinetic energy be 75% of the total energy ?

asked Nov 13, 2018 by pady_1

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The maximum velocity of a particle, executing simple harmonic motion with an amplitude 7 mm, is 4.4 m/s. The period of oscillation is :

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A particle of mass 100 g is thrown vertically upwards with a speed of 5 m/s. The work done by the force of gravity during the time the particle goes up is :

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A mass of M kg is suspened by a weightless string. The horizontal force that is required to displace it until the string makes an angle of $45^{\circ}$ with the initial vertical direction is :

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A whistle producing sound waves of frequencies 9500 Hz and above is approaching a stationary person with speed $\nu \; ms^{-1}$. The velocity of sound in air is $300 \; ms^{-1}$. If the person can hear frequencies upto a maximum of 10,000 Hz, the maximum value of $\nu$ upto which he can hear the whistle is :

asked Nov 13, 2018 by pady_1

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A bomb of mass 16 kg at rest explodes into two pieces of masses $4\; kg$ and $12\; kg$. The velocity of the $12\; kg$ mass id $4\; m^{-1}$. The kinetic energy of the other mass is :

asked Nov 13, 2018 by pady_1

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A particle located at $x=0$ at time $t=0$, starts moving along the positive $x$-direction with a velocity $'v'$ that varies as $v = \alpha \sqrt{x}$. The displacement of the particle varies with time as :

asked Nov 13, 2018 by pady_1

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An electric dipole is placed at an angle of $30^{\circ}$ to a non-uniform electric field. The dipole will experience:

asked Nov 13, 2018 by pady_1

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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 :

asked Nov 13, 2018 by pady_1

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A material 'B' has twice the specific resistance of 'A'. A circular wire made of 'B' has twice the diameter of a wire made of 'A'. Then for the two wires to have the same resistance, the ratio $I_B/I_A$ of their respective lengths must be :

asked Nov 13, 2018 by pady_1

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Needles $N_1, \;N_2$ and $N_3$ are made of a ferromagnetic, a paramagnetic and a diamagnetic substance respectively. A magnet when brought close to them will :

asked Nov 13, 2018 by pady_1

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The Kirchhoff's first law $(\sum i =0)$ and second law $(\sum i R = \sum E)$, where the symbols have their usual meanings, are respectively based on :

asked Nov 13, 2018 by pady_1

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