The radius of the Bohr's first orbit is awhat will be the angular momentum of the electron in the nth orbit ?
  • $ \frac {nh}{2 \pi}$
  • $n^2a_0$
  • $\frac {h}{2n \pi}$
  • $ \frac {2 \pi}{nh}$
A circular ring of Radius a with uniform positive charge density λ per unit length is located in the Y-Z plane with its center at the origin O. A particle of mass M0 and positive charge Q0 is projected from the point S (a√3,0,0) on the positive X axis directly towards O with initial speed vFind the smallest (non zero) value of the speed v0 such that the particle does not return to point S
  • $\sqrt {\frac {Q_0}{2 \lambda M_0 \epsilon _0}}$
  • $\sqrt {\frac {Q_0}{2 M_0 \epsilon _0}}$
  • $\sqrt {\frac {Q_0}{2 a M_0 \epsilon _0}}$
  • $\sqrt {\frac {Q_0 \lambda}{2 M_0 \epsilon _0}}$
A parallel plate capacitor contains one mica sheet of thickness $d_1=1.0 \times 10^{-3} m$ and one fibre sheet of thickness $d_2=.5 \times 10^{-3} m$ The dielectric constants of mica and fibre are 8 and 2.5 respectively . Fibre break down in an electric field of $ 6.4 \times 10^6$ V/m .What maximum voltage can be applied to the capacitor?
  • 6000 V
  • 5200 V
  • 5426 V
  • None of these
A small coil of radius .002 m is placed on the axis of a magnet of magnetic moment $10^5 \; JT^{-1}$ and length .1 m at a distance of .15 m from the center of the magnet Find the net force on coil when a current of 2.0 A is passed through it?
  • $4.4 \times 10^{-3}$ N
  • $4.0 \times 10^{-2}$ N
  • $5.4 \times 10^{-3}$ N
  • $6.4 \times 10^{-3}$ N
A metal disk of radius s rotates with angular velocity ω about a vertical axis through a uniform field B pointing Up. A circuit is made by connecting one end of the resistor to the axle and other end to the the sliding constant which touches the outer edge of the disk.The resistance of the resistor is R. Find the current in the resistor?
  • $\frac {\omega Bs^2}{2R}$
  • $\frac {\omega Bs}{2R}$
  • $\frac {\omega Bs^2}{2R^2}$
  • None of these
A solid sphere of mass M and radius R rolls down an incline plane . which of the following statement is correct
  • K.E is 2/5 rotational and 3/5 translational
  • K.E is 2/9 rotational and 7/9 translational
  • K.E is 1/7 rotational and 6/7 translational
  • K.E is 2/7 rotational and 5/7 translational
The unit of farad-ohm is ?
  • $sec^{-2}$
  • $sec^{-1}$
  • $sec^{2}$
  • $sec$
A bicycle generator creates 3.0 V when bicycle is travelling at a speed of 9.0 km/hr. How much emf is induced when the bicycle is travelling at 15 km/hr?
  • 3.2 V
  • 4 V
  • 5 V
  • None of these
The mean lives of a radio-active substance are 1620 and 405 years for alpha and beta emission respectively. Find the time during which 3/4 of sample will decay if it is decaying both the alpha and beta emission simultaneously?
  • 449 years
  • 550 years
  • 446 years
  • 556 years
The electric potential energy of an isolated metal sphere of radius R with total charge Q is
  • $\frac {Q^2}{2 \pi \epsilon _0 R}$
  • $\frac {Q^2}{3 \pi \epsilon _0 R}$
  • $\frac {Q^2}{24 \pi \epsilon _0 R}$
  • None of these
Which of the following is best neutron moderator?
  • Barium oxide
  • graphite
  • pure water
  • Heavy water
n1 rows,each having n2 cells in series are connected in parallel. This battery is sending maximum current to 3 ohm resistor. The internal resistance of the each cell is .5 ohm then which of the following is true
  • n1=2 and n2=12
  • n1=12 and n2=2
  • n1=4 and n2=6
  • n1=6 and n2=4
A parachutist after bailing out falls 50 m with out friction. When parachute opens ,it decelerates at 2 m/sHe reaches the ground with a speed of 3 m/s. At what height ,did he bail out?
  • 293 m
  • 213 m
  • 200 m
  • 111 m
The time period of a earth satellite in circular orbit is dependent of
  • Radius of the orbit
  • Mass of the satellite
  • Both the mass and radius
  • Neither mass nor radius
A surface S enclosed a electric charge q. Let F be the electric flux passing through it.The flux will be maximum if the surface S is like
  • Cube
  • Spherical
  • cylindrical
  • Same in all the three
If suddenly the gravitational force of attraction between earth and a satellite revolving around it becomes zero,then the satellite will?
  • Move towards earth
  • Becomes stationary in the orbit
  • continue to move in the orbit with same velocity
  • Move tangentially to the original orbit with same velocity
M capacitors of same capacitance C are connected in parallel to the voltage source V.The total energy stored in the capacitor will be?
  • CV
  • $CV^2$
  • $.5MCV^2$
  • $ \frac {.5CV^2}{M}$
A Alpha nucleus of energy $.5 mv^2$ bombards a heavy nuclear target of charge Ze. Then the distance of closest approach for the alpha nucleus will be proportional to
  • $ \frac {1}{Ze}$
  • $ \frac {1}{m}$
  • $v^2$
  • $ \frac {1}{v^4}$
A projectile has been fired with speed 10 m/s making an angle of 30° with the horizontal. Find the angle made by velocity vector of projectile with ground after 2 sec of its firing? Take g=10 m/s2
  • 45°
  • 60°
  • Cant say anything
  • None of the above
The ratio of the concentration of electrons to that of holes in a semiconductor is 7/5 and the ratio of currents is 7/Find the ratio of the drift velocities of electron and holes
  • 5/4
  • 4/5
  • 3/4
  • 4/7
What is the time taken to heat 1 L of water from 10° C to 40° C by a heater of 836 W
  • 40 s
  • 80 s
  • 200 s
  • 150 s
The acceleration of a particle is increasing with time ,then the v-t curve would be like
  • concave Up
  • concave down
  • straight line
  • None of these
A thin ring is rotating about its own axis .If the density of the ring is 11300 Kg/m3,then the maximum permissible linear speed of the ring is
  • 60 m/s
  • 40 m/s
  • 44.6 m/s
  • 42 m/s
Gases begin to conduct electricity at low pressure because
  • atoms break up into electrons and proton's
  • at low pressure gases turn into plasma
  • the electrons in atoms can move freely at low pressure
  • colliding electrons can acquire higher kinetic energy due to increased mean free path leading to ionization of atoms
An LCR series circuit is connected to a source of AC voltage.At resonance ,the phase difference between the applied voltage and current in the circuit is
  • 180°
  • 45°
  • 90°
Two parallel plate air capacitors have their plate areas 100 cm2 and 500 cm2 respectively.If they have the same charge and potential and the distance between the plates of the first capacitor is 0.5 mm, what is the distance between the plates of the second capacitor?
  • .25 cm
  • .1 cm
  • .60 cm
  • 1 cm
Which of these is false for movement of alpha and beta particles in electric and magnetic field
  • Both the article move in circular path in magnetic field
  • curvature of path of beta particle is more than the curvature of alpha particle in magnetic field
  • Deflection of alpha particle is opposite to that beta particle in electric field
  • None of these
If the distance between the earth and sun were half its present value,the number of days in the years would have been
  • 129
  • 730
  • 181
  • 64.5
A body is moving in straight line with a initial velocity u0 and constant acceleration a0 . It covers a distance 40 m in the 4th sec and distance of 60 m in the 6th sec. Which of them are true?
  • $u_0 =5 m/s , a_0=10 m/s^2$
  • $u_0 =5 m/s , a_0=15 m/s^2$
  • $u_0 =15 m/s , a_0=5 m/s^2$
  • $u_0 =10 m/s , a_0=5 m/s^2$
Which all is conserved in Nuclear reactions
  • Energy only
  • Mass only
  • Momentum only
  • Mass,energy and momentum
0 h : 0 m : 1 s