Recent questions in JEEMAIN PAST PAPERS

A sheet of aluminium foil of negligible thickness is introduced between the plates of a capacitor. The capacitance of the capacitor :

asked Dec 11, 2018 by pady_1

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A 3V battery with negligible internal resistance is connected in a circuit as shown in the figure. The current I, in the circuit will be :

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Which of the following cannot be emitted by radioactive substances during their decay ?

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Two identical, photocathodes recieve light of frequencies $f_1$ and $f_2$. If the velocities of the photoelectrons (of mass m) coming out are respecitvely $\nu_1$ and $\nu_2$, then :

asked Dec 11, 2018 by pady_1

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A nucleus with Z = 92 emits the following in a sequence : $\alpha, \; \alpha, \; \beta^-, \; \beta^-,\; \alpha,\; \alpha,\; \alpha, \; \alpha; \; \beta^-,\; \beta^-,\; \alpha,\; \beta^+, \; \beta^+, \; \alpha$. The $Z$ of the resulting nucleus is :

asked Dec 11, 2018 by pady_1

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A radioactive sample at any instant has its disintegration rate 5000 disintegrations per minute. After 5 minutes, the rate is 1250 disintegrations per minute. Then, the decay constant (per minute) is :

asked Dec 11, 2018 by pady_1

1 answer

Let $\overrightarrow{F}$ be the force acting on a particle having position vector $\overrightarrow{r}$ and $\overrightarrow{\tau}$ be the torque of this force about the origin. Then :

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The core of any transformer is laminated so as to :

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In an oscillating LC circuit the maximum charge on the capacitaor is Q. The charge on the capacitor when the energy is stored equally between the electric and magnetic fields is :

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When the current changes from +2A to -2A in 0.05 s, an emf of 8 V is induced in a coil. The coefficient of self-induction of the coil is :

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The displacement y of a wave travelling in the $x$-direction is given by $y = 10^{-4} \sin (600 t - 2x + \frac{x}{3})$ metre, where, $x$ is epressed in metres and $t$ in seconds. The speed of the wave-motion, in $ms^{-1}$ is :

asked Dec 11, 2018 by pady_1

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The length of a simple pendulum executing simple harmonic motion is increase by 21%. The percentage increase in the time period of the pendulum of increased length is :

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Two particles A and B of equal masses are suspended from two massless springs of spring constants $k_1$ and $k_2$, respctively. If the maximum velocities, during oscillations are equal, the ratio of amplitudes of A and B is

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"Heat cannot be itself from a body at lower temperature to a body at higher temperature" is a statement or consequence of :

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A mass M is suspended from a spring of negligible mass. The spring is pulled a little and then released so that the mass executes SHM of time period T. If the mass is increased by $m$, the time period becomes $5T/3$, then the ratio of $\frac{m}{M}$ is :

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The escape velocity for a body projected vertically upwards from the surface of earth is $11\; km/s$. If the body is projected at an angle of $45^{\circ}$ with the vertical, the escape velocity will be :

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A wire suspended vertically from one of its ends is stretched by attaching a weight of 200 N to the lower end. The weight stretches the wire by 1 mm. Then the elastic energy stored in the wire is :

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A light spring balance hangs from the hook of the other light spring balance and a block of mass M kg hangs from the former one. Then the true statement about the scale reading is :

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A block of mass M is pulled along a horizontal frictionless surface by a rope of mass m. If a force P is applied at the free end of the rope, the force exerted by the rope on the block is :

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Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon

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Consider the following two statements : A. Linear momentum of a system of particles is zero. B. Kinetic energy of a system of particle is zero. Then :

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A marble block of mass 2 kg lying on ice when given a velocity of 6 m/s is stopped by friction in 10 s. Then the coefficient of friction is :

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A horizontal force of 10 N is necessary to just hold a block stationary against a wall. The coefficient of friction between the block and the wall is 0.2. The weight of the block is :

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If the electric flux entering and leaving an enclosed surface respectively is $\phi_1$ and $\phi_2$, the electric charge inside the surface will be :

asked Dec 11, 2018 by pady_1

1 answer

Three forces start acting simultaneously on a particle moving with velocity $\overrightarrow{v}$. These forces are represented in magnitude and direcction by the three sides of a triangle ABC (as shown). The particle will now move with velocity :

asked Dec 11, 2018 by pady_1

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The physical quantities not having same dimensions are :

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An ammeter reads upto $1A$. Its internal resistance is $0.81 \Omega$. To increase the range to $10 \;A$, the value of the required shunt is:

asked Dec 11, 2018 by pady_1

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A boy playing on the roof of a 10 m high building throws a ball with a speed of 10 m/s at an angle of $30^{\circ}$ with the horizontal. How far from the throwing point will the ball be at the height of $10 \;m$ from the ground ? [$g = 10\; m/s^2, \; \sin 30^{\circ} = 1/2,\; \cos 30^{\circ} = \sqrt{3}/2]$

asked Dec 11, 2018 by pady_1

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A car moving with a speed of $50\; km/h$, can be stopped by brakes after at least $6 \;m$. If the same car is moving at a speed of $100\; km/h$, the minimum stopping distance is :

asked Dec 11, 2018 by pady_1

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The difference in the variation of resistance with temperature in a metal and a semiconductor arises essentially due to the difference in the :

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Two spherical bodies of mass M and 5M and radii R and 2R respecitvely are released in free space with initial separation between their centres equal to 12 R. If they attract each other due to gravitational force only, then the distance covered by the smaller body just before collision is :

asked Dec 11, 2018 by pady_1

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When $U^{238}$ nucleus originally at rest, decays by emitting an alpha particle having a speed $u$, the recoil speed of the residual nucleus is :

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Which of the following radiations has the least wavelength ?

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A particle performing uniform circular motion has angular momentum L. If its angular frequency is doubled and its kinetic energy halved, then the new angular momentum is :

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The time period of a satellite of earth is 5 hours. If the separation between the earth and the satellite is increased to 4 times the previous value, the new time period will become :

asked Dec 11, 2018 by pady_1

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A circular disc $X$ of radius $R$ is made from an iron plate of thickess $t$, and another disc $Y$ of radius $4R$ is made from an iron plate of thickness $t/4$. Then the relation between the moment of inertia $I_X$ and $I_Y$ is :

asked Dec 11, 2018 by pady_1

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Dimensions of $\frac{1}{\mu_0 \varepsilon_0}$, where symbols have their usual meaning, are :

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The negative $Zn$ pole of Daniell cell, sending a constant current through a circuit, decreases in mass by $0.13\;g$ in $30$ minutes. If the electrochemical equivalent of $Zn$ and $Cu$ are $32.5$ and $31.5$ respectively, the increase in the mass of the positive $Cu$ pole in this time is :

asked Dec 11, 2018 by pady_1

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The thermo-emf of a thermocouple is $25 \; \mu V/^{\circ}C$ at room temperature. A galvanometer of $40 \Omega$ resistance, capable of detecting current as low as $10^{-5}A$, is connected with the thermocouple. The smallest temperature difference that can be detected by this system is :

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Consider telecommunication through optical fibres. Which of the following statements is not true ?

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A strip of copper and another of germanium are cooled from room temperature to 80 K. The resistance of :

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The length of a wire of a potentiometer is 100 cm, and the emf of its stand and cell is E volt. It is employed to measure the emf of a battery whose internal resistance is $0.5 \Omega$. If the balance point is obtained at $l = 30\; cm$ from the positive end, the emf of the battery is :

asked Dec 11, 2018 by pady_1

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A spring balance is attached to the ceiling of a lift. A man hangs his bag on the spring and the spring reads 49 N, when the lift is stationary. If the lift moves downward with an acceleration of 5 m/s, the reading of the spring balance will be :

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Curie temperature is the temperature above which :

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The magnetic lines of force inside a bar magnet :

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A magnetic needle lying parallel to a magnetic field requires $W$ unit of work to turn it through $60^{\circ}$. The torque needed to maintain the needle in this position will be :

asked Dec 11, 2018 by pady_1

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A thin rectangular magnet suspended freely has a period of oscillation equal to $T$. Now it is broken into two equal halves (each having half of the original length) and one piece is made to oscillate freely in the same field. If its period of oscillation is $T'$, the ratio $T'/T$ is :

asked Dec 11, 2018 by pady_1

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A particle of charge $-16 \times 10^{-18} C$ moving with velocity $10\; ms^{-1}$ along the x-axis enters a region where a magnetic field of induction B is along the y-axis and an electric field of magnitude $10^4 V/m$ is along the negative z-axis. If the charged particle continues moving along the x-axis, the magnitude of B is :

asked Dec 11, 2018 by pady_1

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A particle of mass $M$ and charge $Q$ moving with velocity $\overrightarrow{v}$ describes a circular path of radius $R$ when subjected to a uniform transverse magnetic field of induction $B$. The work done by the field when the particle completes one full circle is :

asked Dec 11, 2018 by pady_1

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According to molecular orbital theory, which of the following will not be a viable molecule ?

asked Dec 11, 2018 by pady_1

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