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12th Standard Physics English Medium Free Online Test one mark questions with answer key 2020 - Part Six

12th Standard EM

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Physics

Time : 00:25:00 Hrs
Total Marks : 25
    Answer all the questions 
    25 x 1 = 25
  1. A thin conducting spherical shell of radius R has a charge Q which is uniformly distributed on its surface. The correct plot for electrostatic potential due to this spherical shell is

    (a)

    (b)

    (c)

    (d)

  2. Charge Q on a capacitor varies with voltage Vas shown in graph, where Q is along X-axis and V along Y-axis. The area of triangle OAB represents

    (a)

    capacitance

    (b)

    capacitive reactance

    (c)

    magnetic field between the plates

    (d)

    energy stored in the capacitor

  3. When an electric dipole is placed in a uniform external electric field parallel to the field, it will experience_________.

    (a)

    a torque but no force

    (b)

    a force but no torque

    (c)

    a torque as well as a force

    (d)

    neither a force nor a torque

  4. A wire of resistance 2 ohms per meter is bent to form a circle of radius 1m. Th e equivalent resistance between its two diametrically opposite points, A and B as shown in the fi gure is

    (a)

    \(\pi \Omega\)

    (b)

    \(\frac{\pi}{2}\Omega\)

    (c)

    2\(\pi \Omega\)​​​​​​​

    (d)

    \(\frac{\pi}{4}\Omega\)

  5. Four resistances are connected to a 5V battery of negligible internal resistance as shown what is the potential across \(2\Omega \)?

    (a)

    0.5 V

    (b)

    1:5 V

    (c)

    1.0 V

    (d)

    1.0 V

  6. The potentiometer wire is made of___________

    (a)

    Manganin

    (b)

    Copper

    (c)

    Aluminium

    (d)

    Nichrome

  7. The mobility of an electron is one million times less than that of its specific charge, the mean time taken between two successive collisions is_______

    (a)

    1ms

    (b)

    \(1\mu s\)

    (c)

    1nano sec.

    (d)

    1giga sec

  8. Two identical coils, each with N turns and radius R are placed coaxially at a distance R as shown in the fi gure. If I is the current passing through the loops in the same direction, then the magnetic field at a point P which is at exactly at\(\frac { R }{ 2 } \) distance between two coils is
     
     

    (a)

    \(\frac { 8N{ \mu }_{ ° }I }{ \sqrt { 5 } R } \)

    (b)

    \(\frac { 8N{ \mu }_{ ° }I }{ { 5 }^{ \frac { 3 }{ 2 } }R } \)

    (c)

    \(\frac { 8N{ \mu }_{ ° }I }{ { 5 }R } \)

    (d)

    \(\frac { 4N{ \mu }_{ ° }I }{ \sqrt { 5 } R } \)

  9. Joule's law is verified using

    (a)

    Joule's calorimeter

    (b)

    Joule's voltmeter

    (c)

    Joule's galvanometer

    (d)

    thermometer

  10. Calculate the current passing through a coil of diameter 20 cm, having 50 turns, when the field at the centre of the coil is 200 ampere-turns/ meter

    (a)

    80 ampere

    (b)

    1.6 ampere

    (c)

    0.8 ampere

    (d)

    160 ampere

  11. A circular coil with a cross-sectional area of 4 cm2 has 10 turns. It is placed at the centre of a long solenoid that has 15 turns/cm and a cross-sectional area of 10 cm2. The axis of the coil coincides with the axis of the solenoid. What is their mutual inductance?

    (a)

    7.54 μH

    (b)

    8.54 μH

    (c)

    9.54 μH

    (d)

    10.54 μH

  12. An alternating current has

    (a)

    only positive value

    (b)

    only negative value

    (c)

    both positive and negative value

    (d)

    steady value

  13. The frequency of electromagnetic radiation Hertz produced was _________ Hz.

    (a)

    108

    (b)

    5x107

    (c)

    3x108

    (d)

    6x105

  14. For light incident from air on a slab of refractive index 2, the maximum possible angle of refraction is,

    (a)

    30o

    (b)

    45o

    (c)

    60o

    (d)

    90o

  15. An object 5 cm tall is placed 1m from concave spherical mirror which has a radius of curvature of 20 cm. The size of the image is

    (a)

    0.11 cm

    (b)

    0.50 cm

    (c)

    0.55 cm

    (d)

    0.60 cm

  16. The light photon has _______ nature.

    (a)

    wave

    (b)

    particle

    (c)

    matter

    (d)

    dual

  17. Length contraction is known as ________

    (a)

    Gerner resolution

    (b)

    Thomson contraction

    (c)

    Compton effect

    (d)

    Lorentz-Fitzgerald contraction

  18. The fig. represents the observed intensity of X-rays emitted by an X-ray tube as a function of wavelength. The sharp peaks A and B denote

    (a)

    continuous spectrum

    (b)

    band spectrum

    (c)

    characteristic spectrum

    (d)

    white radiations

  19. Bohr's radius gives the radius of the _________ orbit.

    (a)

    first

    (b)

    second

    (c)

    third

    (d)

    fourth

  20. Why can't we physically join p-type and n-type semiconductor directly to form a p-n junction?

    (a)

    Inter-atomic spacing become less than 1 AO

    (b)

    p -type will repet N-type

    (c)

    There will be discontinuity for the flowing charge carriers

    (d)

    Semi-conducting properties will be lost

  21. Most of the electron in the base of N-P-N transistor flow

    (a)

    out of the base lead

    (b)

    into the collector

    (c)

    into the emitter

    (d)

    into the base supply

  22. Energy gap between valence band and conduction band is called as the _____________

    (a)

    forbidden energy gap

    (b)

    conduction band gap

    (c)

    valence band gap

    (d)

    filled band gap

  23. The most commonly,employed modulation in satellite communication is the

    (a)

    amplititude modulation

    (b)

    FM

    (c)

    phase modulation

    (d)

    all

  24. The materials used in Robotics are

    (a)

    Aluminium and silver

    (b)

    Silver and gold

    (c)

    Copper and gold

    (d)

    Steel and aluminum

  25. Chinese scientists have created the world's first autonomous _________ to combat caner tumours.

    (a)

    RNA Robot

    (b)

    DNA Robot

    (c)

    m RNA Robot

    (d)

    r RNA Robot

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