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In an A.C. circuit, a resistance of R ohm is connected in series with an inductance L. If phase angle between voltage and current be 45o, the value of inductive reactance will be
An electron beam is subjected to perpendicular electric and magnetic fields of 5 x 10-4 wbm-2 and 3 x 103 V m-1 resectively. If there is no deflection, the velocity of electrons is
Consider telecommunication through optical fibres. Which of the following statements is not correct
A parallel plate condenser with oil between the plates (dielectric constant of oil K = 2) has a capacitance C. If the oil is removed, then capacitance of the capacitors becomes
On removing the oil, the capacitance of the capacitor will become.
C ′ = C/K = C/2
The temperature coefficient of resistivity of material is 0.0004/K. When the temperature of the material is increased by 50 oC , its resistivity increases by 2 x 10-8 ohm -meter. The initial resistivity of the material in ohm-meter is
A transformer is used to light a 100W and 110V lamp from a 220V mains. If the main current is 0.5A, the efficiency of the transformer is approximately
If the length of the wire is doubled and its area of cross section is decreased to half, then its resistance
A microammeter has a resistance of 100 Ω and full scale range of 50 μA. It can be used as a voltmeter or as a higher range ammeter provided a resistance is added to it. Pick the correct range and resistance combination
The expected energy of the electrons at the absolute zero is called
In a current carrying long solenoid, the field produced does not depend upon
Which of the following radiations have the least wavelength?
Equal charges are given to two conducting spheres of different radii. The potential will
A charged particle begins to move from the origin in a region which has a uniform magnetic field in the x-direction and a uniform electric field in the y-direction. Its speed is ν, when it reaches the point (x,y,z). The speed (ν) will depend upon
Two charges -10 C and + 10 C are placed 10cm apart. Potential at the centre of the line joining two charges is
The capacitor of a parallel plate capacitor with no dielectric substance and a separation of 0.4 cm is 2 μF. The separation is reduced to half and it is filled with a substance of dielectric value 2.8. The new capacity of the capacitor is
The path of particle moving under the influence of a force fixed in magnitude and direction is
In radioactive decay process, the negatively charged emitted β -particles are
What is the Q-value of the reaction
p + 7Li → 4He + 4He
The atomic masses of 1H , 4He and 7Li are 1.007825 u, 4.002603 u and 7.016004 u respectively
An alpha nucleus of energy 1/2 mv2 bombards a heavy nuclear target of charge Ze. Then the distance of closest approach for the alpha nucleus will be proportional to
Two plane mirrors inclined to each other at an angle 72o , what is the number of images formed?
The minimum potential difference between the base and emitter required to switch a silicon transistor 'ON' is approximately
In a P-type semiconductor the electrical conduction is due to
A p-n photodiode is made of a material with a band gap of 2.0 eV. The minimum frequency of the radiation that can be absorbed by the material is nearly
In intrinsic semiconductor at room temperature, number of electrons and holes are
When Ge crystal are doped with phosphorus atom then it becomes
Light was producing interference have their amplitudes in the ratio 3:2. The intensity ratio of maximum and minimum of interference fringes is
For which property are electrons used in an electron microscope?
According to wave theory, light is a form of energy which travels through a medium in the form of