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

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. Two identical conducting balls having positive charges q1 and q2 are separated by a center to center distance r. If they are made to touch each other and then separated to the same distance, the force between them will be

    (a)

    less than before

    (b)

    same as before

    (c)

    more than before

    (d)

    zero

  2. A non-conducting material which has no free electrons is called

    (a)

    capacitor

    (b)

    Dielectric

    (c)

    conductor

    (d)

    Inductor

  3. The electric flux through a surface will be minimum when the angle between Eand A is

    (a)

    90°

    (b)

    60°

    (c)

    (d)

    45°

  4. 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

  5. A Gaussian surface in the figure is shown by dotted line. The electric field on the surface will be

    (a)

    due to q1 and q2 only

    (b)

    due to q2 only

    (c)

    zero

    (d)

    due to all

  6. A wire connected to a power supply of 230 V has power dissipation P1. Suppose the wire is cut into two equal pieces and connected parallel to the same power supply. In this case power dissipation is P2. The ratio \(\frac{P_2}{P_1}\) is

    (a)

    1

    (b)

    2

    (c)

    3

    (d)

    4

  7. The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 Ω is

    (a)

    0.2 Ω

    (b)

    0.5 Ω

    (c)

    0.8 Ω

    (d)

    1.0 Ω

  8. In a carbon resistor, the third ring represents___________

    (a)

    powers of zeros

    (b)

    powers of ten

    (c)

    ten

    (d)

    infinity

  9. An electron moves straight inside a charged parallel plate capacitor of uniform charge density σ. Th e time taken by the electron to cross the parallel plate capacitor when the plates of the capacitor are kept under constant magnetic fi eld of induction \(\vec { B } \)is

    (a)

    \({ \varepsilon }_{ ° }\frac { eIB }{ \sigma } \)

    (b)

    \({ \varepsilon }_{ ° }\frac { IB }{ \sigma {I} } \)

    (c)

    \({ \varepsilon }_{ ° }\frac { IB }{ {e}\sigma } \)

    (d)

    \({ \varepsilon }_{ ° }\frac { IB }{ \sigma } \)

  10. Which of the following produces large Joule heating effect

    (a)

    IA current through 2Ω resistor for 3 seconds

    (b)

    IA current through 3Ω resistor for 2 seconds

    (c)

    2A current through 1Ω resistor for 2 seconds

    (d)

    3A current through 1Ω resistor for 1 second

  11. Th e fl ux linked with a coil at any instant t is given by \(\Phi\)B =10t2−50t+ 250 . The induced emf at t = 3s is

    (a)

    −190 V

    (b)

    −10 V

    (c)

    10 V

    (d)

    190 V

  12. A step-down transformer reduces the supply voltage from 220 V to 11 V and increase the current from 6 A to 100 A. Then its efficiency is

    (a)

    1.2

    (b)

    0.83

    (c)

    0.12

    (d)

    0.9

  13. Which current- time graph represents the steady movement of short magnet through a coil XY?

    (a)

    (b)

    (c)

    (d)

  14. In a single phase dynamo, the direction of the induced current is given by __________

    (a)

    Faraday's laws

    (b)

    Maxwell's equations

    (c)

    Einstein's equation

    (d)

    Fleming's right hand rule

  15. The instantaneous current in an AC circuit containing a pure inductor is i = Io sinωt, The instantaneous emf is: The

    (a)

    e = Eosin\(\left( \omega t+\frac { \pi }{ 2 } \right) \)

    (b)

    e = Eosin\(\left( \omega t-\frac { \pi }{ 2 } \right) \)

    (c)

    e=Eosin(ωt - π)

    (d)

    e = Eosin

  16. During the propagation of electromagnetic waves in a medium

    (a)

    electric energy density is double of the magnetic energy density

    (b)

    electric energy density is half of the magnetic energy density

    (c)

    electric energy density is equal to the magnetic energy density

    (d)

    both electric and magnetic energy densities are zero

  17. The phase difference between electric and magnetic field vectors in the electromagnetic waves?

    (a)

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

    (b)

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

    (c)

    \(\pi\)

    (d)

    zero

  18. Stars twinkle due to,

    (a)

    reflection

    (b)

    total internal refl ection

    (c)

    refraction

    (d)

    polarisation

  19. Light transmitted by Nicol prism is,

    (a)

    partially polarised

    (b)

    unpolarised

    (c)

    plane polarised

    (d)

    elliptically polarised

  20. If a light of wavelength 330 nm is incident on a metal with work function 3.55 eV, the electrons are emitted. Then the wavelength of the emitted electron is (Take h = 6.6 × 10–34 Js)

    (a)

    <2.75×10−9m

    (b)

    ≥2.75×10−9m

    (c)

    ≤2.75×10−12m

    (d)

    <2.5×10−10m

  21. When the intensity of a light source is increased

    (a)

    the number of photons emitted by the source in unit time increases

    (b)

    more energetic photons are emitted

    (c)

    faster photons are emitted

    (d)

    total energy of the photons emitted per unit time decreases.

  22. Below the threshold frequency, if the intensity of radiation is increased, the emission of photoelectrons _______

    (a)

    increases

    (b)

    decreases

    (c)

    is zero

    (d)

    is a constant

  23. mirror of focal length of f and the maximum and minimum distance of

    (a)

    1

    (b)

    2

    (c)

    3

    (d)

    4

  24. Doping a semiconductor results in

    (a)

    The decrease in mobile charge carriers

    (b)

    The change in chemical properties

    (c)

    The change in the crystal structure

    (d)

    The breaking of the covalent bond

  25. The particle size of ZnO material is 30 nm. Based on the dimension it is classified as

    (a)

    Bulk material

    (b)

    Nanomaterial

    (c)

    Soft material

    (d)

    Magnetic material

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