Recent questions tagged set a

$_p K_a$ 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

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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

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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

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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

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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

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$\Delta U$ is equal to

asked Jul 27, 2017 by meena.p

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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

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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

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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

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Which of the following statements is false ?

asked Jul 26, 2017 by meena.p

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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

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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

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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

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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

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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

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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

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In the above circuit the current in each resistance is :

asked Jul 26, 2017 by meena.p

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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

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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

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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

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A particle is executing simple harmonic motion with a time period T. At time $t=0$, it is at its position of quilibrium. The kinetic energy - time graph of the particle will look like

asked May 31, 2017 by meena.p

1 answer

The temperature of an open room of volume $30 m^3$ increases from $17^{\circ}C$ to $27^{\circ}C$ due to the sunshine. The atmospheric pressure in the room remains $1×10^5\; Pa$.If $n_i$ and $n_f$ are the number of molecules in the room before and after heating, then $n_f−n_i$ will be :

asked May 31, 2017 by meena.p

1 answer

$C_p$ and $C_v$ are specific heats at constant pressure and constant volume respectively. It is observed that $C_p−C_v=a$ for hydrogen gas $Cp−Cv=b$ for nitrogen gas The correct relation between a and b is :

asked May 31, 2017 by meena.p

1 answer

An external pressure P is applied on a cube at $0^{\circ}C$ so that it is equally compressed from all sides. K is the bulk modulus of the material of the cube and α is its coefficient of linear expansion. Suppose we want to bring the cube to its original size by heating. The temperature should be raised by :

asked May 31, 2017 by meena.p

1 answer

A copper ball of mass $100\; gm $is at a temperature T. It is dropped in a copper calorimeter of mass $100\; gm$, filled with $170\; gm$ of water at room temperature.Subsequently, the temperature of the system is found to be $75^{\circ}C$. T is given by : (Given : room temperature$=30^{\circ}C$, specific heat of copper $=0.1\; cal/gm^{\circ}C)$

asked May 31, 2017 by meena.p

1 answer

The variation of acceleration due to gravity $g$ with distance d from centre of the earth is best represented by (R=Earth’s radius) :

asked May 30, 2017 by meena.p

1 answer

A slender uniform rod of mass M and length l is pivoted at one end so that it can rotate in a vertical plane (see figure). There is negligible friction at the pivot. The free end is held vertically above the pivot and then released. The angular acceleration of the rod when it makes an angle $\theta$ with the vertical is :

asked May 30, 2017 by meena.p

1 answer

The moment of inertia of a uniform cylinder of length l and radius R about its perpendicular bisector is $I$. What is the ratio $\large\frac{l}{R}$ such that the moment of inertia is minimum ?

asked May 30, 2017 by meena.p

1 answer

A time dependent force $F=6t$ acts on a particle of mass $1\;kg$. If the particle starts from rest, the work done by the force during the first 1 sec. will be :

asked May 30, 2017 by meena.p

1 answer

A body of mass $m=10^{−2}\; kg$ is moving in a medium and experiences a frictional force $F=−kv^2$. Its initial speed is $v_0=10 ms^{−1}$. If, after $10\;s$, its energy is $\large\frac{1}{8}$$ \;mv_0^2$,the value of k will be :

asked May 29, 2017 by meena.p

1 answer

A body is thrown vertically upwards. Which one of the following graphs correctly represent the velocity vs time ?

asked May 29, 2017 by meena.p

1 answer

A man grows into a giant such that his linear dimensions increase by a factor of 9. Assuming that his density remains same, the stress in the leg will change by a factor of :

asked May 29, 2017 by meena.p

1 answer

The Boolean Expression $(p \wedge \sim q) \vee q \vee (\sim p \wedge q)$\ is quivalent to :

asked Mar 22, 2017 by meena.p

1 answer

A man is walking towards a vertical pillar in a straight path, at a uniform speed. At a certain point A on the path, he observes that the angle of elevation of the top of the pillar is $30^{\circ}$. After walking for 10 minutes from A in the same direction, at a point B, he observes that the angle of elevation of the top of the pillar is $60^{\circ}$. Then the time taken (in minutes) by him, from B to reach the pillar, is :

asked Mar 22, 2017 by meena.p

1 answer

If $0 \leq x < 2 \pi$, then the number of real values of $x$, which satisfy the equation $\cos x + \cos 2x = \cos 3x + \cos 4x = 0,$ is :

asked Mar 22, 2017 by meena.p

1 answer

Let two fair six-faced dice A and B be thrown simultaneously. If $E_1$ is the event that die $A$ shows up four, $E_2$ is the event that die B shows up two and $E_3$ is the event that the sum of numbers on both dice is odd, then which of the following statements is NOT true?

asked Mar 21, 2017 by meena.p

1 answer

If the standard deviation of the numbers $2, 3, a$ and $11$ is $3.5,$ then which of the following is true?

asked Mar 21, 2017 by meena.p

1 answer

Let $\overrightarrow{a}, \overrightarrow{b}$ and $\overrightarrow{c}$be three unit vectors such that $\overrightarrow{a} \times (\overrightarrow{b} \times \overrightarrow{c}) = \large\frac{3}{2}(\overrightarrow{b}+\overrightarrow{c})$. If $\overrightarrow{b}$ If $\overrightarrow{b}$ is not parallel to $\overrightarrow{c}$ , then the angle between $\overrightarrow{a}$ and $\overrightarrow{b}$ is :

asked Mar 21, 2017 by meena.p

1 answer

If the line, $\large\frac{x-3}{2} =\frac{y+2}{-1}=\frac{z-4}{3}$ lies in the plane,$lx + my - z = 9,$ then $l^2+m^2$ is equal to :

asked Mar 21, 2017 by meena.p

1 answer

The eccentricity of the hyperbola whose length of the latus rectum is equal to 8 and the length of its conjugate axis is equal to half the distance between its foci, is:

asked Mar 21, 2017 by meena.p

1 answer

Let P be the point on the parabola, $y^2= 8x$ which is at a minimum distance from the centre $C$ of the circle, $x^2+(y + 6)^2= 1.$ Then the equation of the circle, passing through C and having its centre at P is:

asked Mar 21, 2017 by meena.p

1 answer

If one of the diameters of the circle, given by the equation, $x^2 + y^2-4x+6y -12 = 0,$ is a chord of a circle S, whose centre is at $(-3, 2),$ then the radius of S is:

asked Mar 21, 2017 by meena.p

1 answer

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