Test Series-11

## Instructions

• Your test contains 12 multiple choice questions with only one answer
• This is 30 min test.Please make sure you complete it in stipulated time
• You can Finish this test any time using 'Submit' button.
• Once finished you get a chance to review all question with correct answers and their solutions.

1.The radius of the Bohr's fisrt orbit is a0. what will be the angular momentum of the electron in the nth orbit ?
• nh/2π
• n2a0
• h/2nπ
• 2π/nh

2.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 v0. Find the smallest (non zero) value of the speed v0 such that the particle does not return to point S
• $\sqrt{\frac{{Q}_{0}}{2{\mathrm{\lambda M}}_{0}{\epsilon }_{0}}}$
• $\sqrt{\frac{{Q}_{0}}{2{M}_{0}{\epsilon }_{0}}}$
• $\sqrt{\frac{{Q}_{0}}{2{M}_{0}a{\epsilon }_{0}}}$
• $\sqrt{\frac{{Q}_{0}\lambda }{2{M}_{0}{\epsilon }_{0}}}$

3.A parallel plate capacitor contains one mica sheet of thickness d1=1.0X10-3m and one fibre sheet of thickness d2=.5X10-3\ The dielectric constants of mica and fibre are 8 and 2.5 respectively . Fibre break down in an electric field of 6.4X106 V/m .What maximum voltage can be applied to the capacitor?
• 6000V
• 5200V
• 5426V
• None of these

4..A small coil of radius .002 m is placed on the axis of a magnet of magnetic moment 105 JT-1 and lenght .1 m at a distance of .15m from the center of the magnet Find the net force on coil when a current of 2.0 A is passed through it?
• 4.4X10-3 N
• 4.0X10-2 N
• 5.4X10-3 N
• None of these

5.A metal disk of radius s rotates with angular velocity ω about a vertical axis through a uniform field B poiting Up. A circuit is made by connecting one end of the resistor to the axle and other end to the the sliding contant which touches the outer edge of the disk.The resistance of the resistor is R. Find the current in the resistor?
• $\frac{\mathrm{\omega B}{s}^{2}}{2R}$
• $\frac{\mathrm{\omega B}{s}^{}}{2R}$
• $\frac{\mathrm{\omega B}{s}^{}}{2{R}^{2}}$
• None of these

6. A solid sphere of mass M and radius R rolls down an incline plane . which of the following statement is correct
• KE is 2/5 rotational and 3/5 translational
• KE is 2/9 rotational and 7/9 translational
• KE is 1/7 rotational and 6/7 translational
• KE is 2/7 rotational and 5/7 translational

7. The unit of farad-ohm is ?
• sec-2
• sec-1
• sec2
• sec

8. A bicyle generator creates 3.0 V when bicycle is travelling at a speed of 9.0 km/hr. How much emf is induced when the bicyle is travelling at 15 km/hr?
• 3.2
• 4V
• 5V
• None of these

9.The mean lives of a radio-active substance are 1620 and 405 years for alpha and beta emmision respectively. Find the time during which 3/4 of sample will decay if it is decaying both the alpha and beta emmision simultanously?
• 449 years
• 550 years
• 446 years
• 556 years

10.The electric potential energy of an isolated metal sphere of radius R with total charge Q is
• $\frac{{Q}^{2}}{8\pi {\epsilon }_{0}R}$
• $\frac{{Q}^{2}}{3\pi {\epsilon }_{0}R}$
• $\frac{{Q}^{2}}{24\pi {\epsilon }_{0}R}$
• None of these

11. Which of the following is best neutron moderator
• Barium oxide
• graphite
• pure water
• Heavy water

12. n1 rows,each having n2 cells in series are connected in parallel. This battery is sending maximum current to 3ohm resistor. The internal resistance of the each cell is .5ohm 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