Recent questions tagged 2004

When p-n junction diode is forward biased

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The manifestation of band structure in solids is due to

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A piece of copper and another of germanium are cooled from room temperature to 77 K, the resistance of

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For a transistor amplifier in common emitter configuration having load impedance of $1 \; k \Omega\; (h_{fe} = 50$ and $h_{oe} = 25)$ the current gain is

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When npn transistor is used as amplifier

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An $\alpha$-particle of energy $5 \;MeV$ is scattered through $180^{\circ}$ by a fixed uranium nucleus. The distance of the closest approach is of the order of

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The binding energy per nucleon of deuteron $(_1^2H)$ and helium nucleus $(_2^4 He)$ is $1.1\; MeV$ and $7\; MeV$ respectively. If two deuteron nuclei react to form a single helium nucleus, then the energy released is

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A nucleus disintegrates into two nuclear parts which have their velocities in the ratio $2:1$. The ratio of their nuclear sizes will be

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A charged oil drop is suspended in a uniform field of $3 \times 10^4 V/m$ so that it neither falls nor rises. The charge on the drop will be (take the mass of the charge = $9.9 \times 10^{-15} kg$ and $g = 10\;m/s^2$)

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The work function of a substance is 4.0 eV. Then longest wavelength of light that can cause photoelectron emission from this substance approximately

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According to Einstein's photoelectric equation, the plot of the kinetic energy of the emitted photo electrons from a metal $V_s$ the frequency, of the incident radiation gives straight line whose slope

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A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 radians per second. If the horizontal component of earth's magnetic field is $0.3 \times 10^{-4}T$, then the e.m.f. developed between the two ends of the conductor is

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In a LCR circuit capacitance is changed from C to 2C. For the resonant frequency to remain unchanged, the inductance should be changed from L to

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In a uniform magetic field of induction B a wire in the form of semicircle of radius r rotates about the diameter of the circle with angular frequency $\omega$. The axis of rotation is perpendicular to the field. If the total resistance of the circuit is R the mean power generated per period of rotation is

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A coil having n turns and resistance $4 R \Omega$. This combination is moved in time t seconds from a magnetic field $W_1$ weber to $W_2$ weber. The induced current in the circuit is

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In an LCR series a.c. circuit, the voltage across each of the components, L, C and R is 50 V. The voltage across the LC combination will be

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The materials suitable for making electromagnets should have

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The length of a magnet is large compared to its width and breadth. The time period of its width and breadth. The time period of its oscillation in a vibration magnetometer is 2 s. The magnet is cut along its length into three equal parts and three parts are then placed on each other with their like poles together. The time period of this combination will be

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Two long conductors, separated by a distance $d$ carry current $I_1$ and $I_2$ in the same direction. They exert a force $F$ on each other. Now the current in one of them increased to two times and its direction reversed. The distance is also increased to $3d$. The new value of the force between them is

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The magnetic field due to a current carrying circular loop of radius 3 cm at a point on the axis at a distance of 4 cm from the centre is 54 $\mu$T. What will be its value at the centre of the loop ?

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A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. It is then bent into a circular loop of n turns. The magnetic field at the centre of the coil will be

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A current I ampere flows along an infinitely long straight thin walled tube, then the magnetic induction at any point inside the tube is

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The electrochemical equivlent of a metal is $3.3 \times 10^{-7}$ kg per coulomb. The mass of the metal liberated at the cathode when a 3A current is passed for 2 seconds will be

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The thermo emf of a thermocouple varies with the temperature $\theta$ of the hot junction as $E= a \theta + b \theta^2$ in volts where the ratio $a/b$ is $700^{\circ}C$. If the cold junction is kept at $0^{\circ}C$, then the neutral temperature is

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Time taken by a 836 W heater to heat one litre of water from $10^{\circ}C$ to $40^{\circ}C$ is

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The thermistors are usually made of

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In a metre bridge experiment null point is obtained at 20 cm from one end of the wire when resistance X is balanced against another resistance Y. If X < Y, then where will be the new position of the null point from the same end, if one decides to balance a resistance of 4X against Y?

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An electric current is passed through a circuit containing two wires of the same material, connected in parallel. If the length and radii of the wires are in the ratio of 4/3 and 2/3, then the ratio of the currents passing through the wire will be

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The resistance of the series combination of two resistances is S. When they are joined in parallel through total resistance is P. If $S=nP$, then the minimum possible value of n is

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The total current supplied to the circuit by the battery is <br>

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Alternating current can not be measured by D.C. ammeter because

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Four charges equal to -Q are placed at the four corners of a square and a charge q is at its centre. If the system is in equilibrium the value of q is

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A charged particle q is shot towards another charged particle Q which is fixed, with a speed v it approaches Q upto a closest distance r and then returns. If q were given a speed 2v, the closest distances of approach would be

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Two spherical conductor B and C having equal radii and carrying equal charges in them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that of B but uncharged brought in contact with B, then brought in contact with C and finally removed away from both. The new force of repulsion, between B and C is

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An electromagnetic wave of frequency $v =3.0 \;MHz$ passes from vacuum into a dielectric medium with permittivity $\varepsilon = 4.0$. Then

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The maximum number of possible interference maxima for slit-separation equal to twice the wavelength in Young's double-slit experiment is

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The angle of incidence at which reflected light totally polarized for reflection from air to glass (refractive index n), is

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A plane convex lens of refractive index 1.5 and radius of curvature 30 cm is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of the size of the object ?

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A light ray is incident perpendicular to one face of a $90^{\circ}$ prism and is totally internally reflected at the glass-air interface. If the angle of reflection is $45^{\circ}$, we conclude that the refractive index $n$ <br>

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The temperature of two outer surface of a composite slab, consisting of two materials having coefficients of thermal conductivity $K$ and $2K$ and thickness $x$ and $4x$, respectively are $T_2$ and $T_1 (T_2> T_1)$. The rate of heat tranfer through the slab, in a steady state is $(\frac{A(T_2 - T_1) K}{x})f$, with $f$ equal to <br>

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A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is

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Two thermally insulated vessels 1 and 2 are filled with air at temperatures $(T_1, \; T_2)$, volume $(V_1, \; V_2)$ and pressure $(P_1, \; P_2)$ respectively. If the value joining two vessels is opened, the temperature inside the vessel at equilibrium will be

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Which of the following statements is correct for any thermodynamic system ?

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If the temperature of the Sun were to increase from $T$ to $2T$ and its radius from $R$ to $2R$, then the ratio of the radiant energy received on earth to what it was previously will be

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One mole of ideal monoatomic gas $(\gamma = 5/30)$ is mixed with one mole of diatomic gas $(\gamma = 7/5)$. What is $\gamma$ for the mixture ? $\gamma$ denotes the ratio of specific heat at constant pressure, to that at constant volume.

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In forced oscillation of a particle the amplitude is maximum frequency $\omega_1$ of the force, while the energy is maximum for a frequency $\omega_2$ of the force, then

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A particle of mass $m$ is attached to a spring (of spring constant $k$) and has a natural angular frequency $\omega_0$. An external force $F(t)$ proportional to $\cos \omega t ( \omega \neq \omega_0)$ is applied to the oscillator. The time displacement of the oscillator will be proportional to

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The displacement $y$ of a particle in a medium can be expressed as $y = 10^{-6} \sin (110 t + 20 x + \pi/4)\;m$ where $t$ is in seconds and $x$ in meter. The speed of the wave is

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The total energy of particle, executing simple harmonic motion is

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A particle at the end of a spring executes simple harmonic motion with a period $t_1$, while the corresponding period for another spring is $t_2$. If the period of oscillation with the two springs in series is $t$, then

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