Recent questions in JEEMAIN PAST PAPERS

Phosphorus pentacloride dissociates as follows, in a closed reaction vessel, $PCl_5 (g) \rightleftharpoons PCl_3 (g) + Cl_2(g) $ If total pressure at equilibrium of the reaction mixture is $P$ and degree of dissociation of $PCl_5$ is $x$, the partial pressure of $PCl_3$ will be :

asked Nov 13, 2018 by pady_1

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Uncertainty in the position of an electron (mass $9.1 \times 10^{-31} kg$) moving with a velocity $300\; ms^{-1}$, accurate upon $0.001 \%$ will be : ($ h = 6.63 \times 10^{-34} Js$)

asked Nov 13, 2018 by pady_1

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The increasing order of stability of the following free radicals is :

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Among the following the one that gives positive iodoform test upon reaction with $I_2$ and $NaOH$ is :

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The pyrimidine bases present in DNA are :

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$CH_3Br + Nu^- \to CH_3 - Nu + Br^-$ The decreasing order of the rate of the above reaction with nucleophiles $(Nu^-)$ A to D is : [$Nu^- = (A)\; PhO,\; (B)\; AcO^-,\; (C)\; HO^-\; (D)\; CH_3O$]

asked Nov 13, 2018 by pady_1

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Phenyl magnesium bromide reacts with methanol to give :

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In the transformation of $_{92}^{238}U$ to $_{92}^{234}U$, if one emission is an $\alpha$-particle, what should be the other emission (s) ?

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The term anomers of glucose refers to :

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The IUPAC name for the complex $[Co(NO_2)(NH_3)_5]Cl_2$ is :

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Which of the following chemical reactions depicts the oxidizing behaviour of $H_2SO_4$ ?

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A reaction was found to be second order with respect to the concentration of carbon monoxide. If the concentration of carbon monoxide is doubled, with everything else kept the same, the rate of reaction will :

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Total volume of atoms present in a face-centred cubic unit cell of a metal is (r is atomic radius) :

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Which of the following molecules/ions does not contain unpaired electrons ?

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According to Bohr's theory, the angular momentum of an electron in 5th orbit is :

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How many moles of magnesium phosphate, $Mg_3 (PO_4)_2$ will contain 0.25 mole of oxygen atoms ?

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The increaing order of the rate of HCN addition to compound A-D is : (A) $HCHO$ (B) $CH_3COCH_3$ (C) $PhCOCH_3$ (D) $PhCOPh$

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The IUPAC name of the compound shown below is :

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$HBr$ reacts with $CH_2 = CH - OCH_3$ under anhydrous conditions at room temperature to give :

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If the terminal speed of a sphere of gold (density = $19.5 \; kg/m^3$) is $0.2 \; m/s$ in a viscous liquid (density = $1.5\; kg/m^3$), find the terminal speed of a sphere of silver (density = $10.5 \; kg/m^3$) of the same size in the same liquid.

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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 :

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If the lattice constant of this semiconductor is decreased, then which of the following is correct ?

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The work of 146 kJ is performed in order of compress one kilo mole of a gas adiabatically and in this process the temperature of the gas increases by $7^{\circ}C$. The gas is : ($R = 8.3 \; J\; mol^{-1} K^{-1}$)

asked Nov 13, 2018 by pady_1

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Two rigid boxes containing different ideal gases are placed on a table. Box A contains one mole of nitrogen at temperature $T_0$, while box B contains one mole of helium at temperature $(7/3) T_0$. The boxes are then put into thermal contact with each other, and heat flows between them until the gases reach a common final temperature (Ignore the heat capacity of boxes). Then, the final temperature of the gases, $T_f$ in terms of $T_0$ is :

asked Nov 13, 2018 by pady_1

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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 $\omega'$.

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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:

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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 :

asked Nov 13, 2018 by pady_1

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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 :

asked Nov 13, 2018 by pady_1

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

asked Nov 13, 2018 by pady_1

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

asked Nov 13, 2018 by pady_1

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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 :

asked Nov 13, 2018 by pady_1

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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 :

asked Nov 13, 2018 by pady_1

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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 :

asked Nov 13, 2018 by pady_1

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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 :

asked Nov 13, 2018 by pady_1

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

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