Recent questions in JEEMAIN-2017

Which of the following species is not paramagnetic ?

asked Jul 28, 2017 by meena.p

0 answers

Both lithium and magnesium display several similar properties due to the diagonal relationship; however, the one which is incorrect, is :

asked Jul 28, 2017 by meena.p

1 answer

$_p K_a$ of a weak acid (HA) and $_pK_b$ of a weak base $(BOH)$ are 3.2 and 3.4, respectively.The pH of their salt (AB) solution is :

asked Jul 28, 2017 by meena.p

1 answer

Two reactions $R_1$ and $R_2$ have identical pre-exponential factors. Activation energy of $R_1$ exceeds that of $R_2$ by $10 kJ mol^{−1}$. . If $k_1$ and $k_2$ are rate constants for reactions $R_1$ and $R_2$ respectively at $300\; K$, then $ln(k2/k1)$ is equal to : $(R=8.314 \;J \;mol^{−1} K^{−1} )$

asked Jul 27, 2017 by meena.p

0 answers

The radius of the second Bohr orbit for hydrogen atom is :(Planck’s Const.h= $6.6262 \times 10^{-34}\;Js$ mass of electron $= =9.1091 \times 10^{−31}\; kg;$ charge of electron $e= 1.60210 \times 10^{-19}\;C$ permittivity of vacuum$\in_0 =8.854185 \times 10^{-12} \;kg^{-1} m ^{-3} A^2)$

asked Jul 27, 2017 by meena.p

0 answers

The freezing point of benzene decreases by $0.45^{\circ}C$ when $0.2\; g \%$ of acetic acid is added to $20\; g$ of benzene. If acetic acid associates to form a dimer in benzene,percentage association of acetic acid in benzene will be : $(Kf$ for benzene=$5.12 \;K \;kg mol^{−1})$

asked Jul 27, 2017 by meena.p

0 answers

Given $E^{\circ} _{Cl_2/Cl^{-}} =1.36 \;V, E^{\circ} _{Cr^{3+}/Cr} =-0.74\;V \\ E^{\circ} _{Cr_2O_7^{2-}} =1.33 \;V, E^{\circ} _{MnO_4^{-}/Mn^{2+}} =1.51 \;V $ Among the following, the strongest reducing agent is :

asked Jul 27, 2017 by meena.p

0 answers

A metal crystallises in a face centred cubic structure. If the edge length of its unit cell is ‘a’, the closest approach between two atoms in metallic crystal will be :

asked Jul 27, 2017 by meena.p

1 answer

The Tyndall effect is observed only when following conditions are satisfied (a) The diameter of the dispersed particles is much smaller than the wavelength of the light used. (b) The diameter of the dispersed particle is not much smaller than the wavelength of the light used. (c) The refractive indices of the dispersed phase and dispersion medium are almost similar in magnitude. (d) The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.

asked Jul 27, 2017 by meena.p

0 answers

$\Delta U$ is equal to

asked Jul 27, 2017 by meena.p

0 answers

1 gram of a carbonate $(M_2CO_3)$ on treatment with excess HCl produces $0.01186$ mole of $CO_2$ . The molar mass of $M_2CO_3$ in $g\; mol^{−1}$ is :

asked Jul 27, 2017 by meena.p

0 answers

Given $C_{(graphite)}+O_2 (g) \to CO_2(g) ; \Delta_r H^{\circ} =-393.5\;kj\;mol^{-1}\\$ $H_2(g)+\large\frac{1}{2}$$O_2(g) \to H_2O(l) ; \Delta_r H^{\circ} =-285.8\;kj\;mol^{-1}\\$ $CO_2(g)+2H_2O(l) \to CH_4(g) +2O_2(g) ; \Delta_{r}H^{\circ} =+890.3\;kJ mol^{-1}\\$ Based on the above thermochemical equations, the value of $\Delta_r H^{\circ}$ at $298\; K$ for the reaction $ C_{(graphite)}+2H_2(g) \to CH_4(g) $ will be

asked Jul 27, 2017 by meena.p

0 answers

The following observations were taken for determining surface tension T of water by capillary method :diameter of capillary, $D= 1.25 \times 10^{-2}\;m$ rise of water, $h= 1.45 \times 10^{-2}\;m$ Using $g= 9.80 m/s^2$ and the simplified relation $T= \large\frac{rhg}{2}\times 10^3 N/m$, the possible error in surface tension is closest to :

asked Jul 26, 2017 by meena.p

0 answers

Which of the following statements is false ?

asked Jul 26, 2017 by meena.p

0 answers

In amplitude modulation, sinusoidal carrier frequency used is denoted by $\omega_c$ and the signal frequency is denoted by $\omega _m$ The bandwidth $(\Delta \omega _m)$ of the signal is such that $\Delta \omega_m << \omega_c$ . Which of the following frequencies is not contained in the modulated wave ?

asked Jul 26, 2017 by meena.p

1 answer

In a common emitter amplifier circuit using an n-p-n transistor, the phase difference between the input and the output voltages will be :

asked Jul 26, 2017 by meena.p

0 answers

A radioactive nucleus A with a half life T,decays into a nucleus B. At t=0, there is no nucleus B. At sometime t, the ratio of the number of B to that of A is 0.3. Then, t is given by :

asked Jul 26, 2017 by meena.p

0 answers

Some energy levels of a molecule are shown in the figure. The ratio of the wavelengths $r=\large\frac{\lambda _1}{\lambda_2}$, is given by :

asked Jul 26, 2017 by meena.p

0 answers

A particle A of mass m and initial velocity $v$ collides with a particle $B$ of mass $\large\frac{m}{2}$ which is at rest. The collision is head on, and elastic. The ratio of the de-Broglie wavelengths $\lambda_A$ to $\lambda_B$ after the collision is :

asked Jul 26, 2017 by meena.p

1 answer

In a Young’s double slit experiment, slits are separated by $0.5\; mm$, and the screen is placed $150\; cm$ away. A beam of light consisting of two wavelengths, $650 \;nm$ and $520\; nm$, is used to obtain interference fringes on the screen. The least distance from the common central maximum to the point where the bright fringes due to both the wavelengths coincide is :

asked Jul 26, 2017 by meena.p

0 answers

A diverging lens with magnitude of focal length 25 cm is placed at a distance of 15 cm from a converging lens of magnitude of focal length 20 cm. A beam of parallel light falls on the diverging lens. The final image formed is :

asked Jul 26, 2017 by meena.p

1 answer

An electron beam is accelerated by a potential difference V to hit a metallic target to produce X-rays. It produces continuous as well as characteristic X-rays.If $\lambda_{min}$ is the smallest possible wavelength of X-ray in the spectrum, the variation of log $\lambda_{min}$ with log V is correctly represented in :

asked Jul 26, 2017 by meena.p

0 answers

In a coil of resistance $100 \Omega$ , a current is induced by changing the magnetic flux through it as shown in the figure. The magnitude of change in flux through the coil is :

asked Jul 26, 2017 by meena.p

0 answers

When a current of $5 \;mA$ is passed through a galvanometer having a coil of resistance $15 \Omega$, it shows full scale deflection. The value of the resistance to be put in series with the galvanometer to convert it into a voltmeter of range $0−10\; V$ is :

asked Jul 26, 2017 by meena.p

2 answers

A magnetic needle of magnetic moment $6.7 \times 10^{-2}Am^2$ and moment of inertia $7.5 \times 10^{-6}\;kg \;m^2$ is performing simple harmonic oscillations in a magnetic field of $0.01\; T$. Time taken for 10 complete oscillations is :

asked Jul 26, 2017 by meena.p

0 answers

In the above circuit the current in each resistance is :

asked Jul 26, 2017 by meena.p

0 answers

In the given circuit diagram when the current reaches steady state in the circuit,the charge on the capacitor of capacitance C will be :

asked Jul 26, 2017 by meena.p

0 answers

A capacitance of $2 \mu F$ is required in an electrical circuit across a potential difference of $1.0\; kV$. A large number of $1\; \mu F$ capacitors are available which can withstand a potential difference of not more than $300\; V$. The minimum number of capacitors required to achieve this is :

asked Jul 26, 2017 by meena.p

0 answers

An electric dipole has a fixed dipole moment $\overrightarrow{p}$, which makes angle θ with respect to x-axis. When subjected to an electric field $\overrightarrow{E_1}= E \hat i $, it experiences a torque $\overrightarrow{T_1}= \tau \hat {k}$. When subjected to another electric field $\overrightarrow{E_2}= \sqrt 3 E_1 \hat j $ it experiences a torque $\overrightarrow{T_2}= -\overrightarrow{T_1}$. The angle $\theta$ is :

asked Jul 26, 2017 by meena.p

0 answers

An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency $10\; GHz$. What is the frequency of the microwave measured by the observer ? (speed of light $=3 \times 10^8 ms^{−1}$ )

asked Jul 25, 2017 by meena.p

0 answers