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Modern Physics Test - 2
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Modern Physics Test - 2
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  • Question 1/10
    4 / -1

    A radioactive material decays by simultaneous emission of two particles with respective half-lives 1620 and 810 years.
    The time, in years, after which one-fourth of the material remains is

    Solutions

    when No is initial number of atoms

  • Question 2/10
    4 / -1

    The probability of electrons to be found in the conduction band of an intrinsic semiconductor at a finite temperature

    Solutions

    KEY CONCEPT : For a semi conductor n = n0e–Eg/kT where n0 = no. of free electrons at absolute zero, n = no. of free electrons at T kelvin, Eg = Energy gap, k = Boltzmann constant.
    As Eg increases, n decreases exponentially.

  • Question 3/10
    4 / -1

    A full-wave rectifier circuit along with the out-put is shown in Figure. The contribution (s) from the diode 1 is (are)

    Solutions

    As shown in the fig. (i) during one half cycle the polarity of P and S are opposite such that diode (1) is reversed biased and hence non conducting.

    During the other half cycle, diode (1) gets forward biased and is conducting. Thus diode (1) conducts in one half cycle and does not conduct in the other so the correct option is (b) (a and c.)

  • Question 4/10
    4 / -1

    As per Bohr model, the minimum energy (in eV) required to remove an electron from the ground state of doubly ionized Li atom (Z = 3) is

    Solutions

    KEY CONCEPT :

    Therefore, ground state energy of doubly ionized lithium atom (Z = 3, n = 1) will be

    ∴ Ionization energy of an electron in ground state of doubly ionized lithium atom will be 122.4eV.

  • Question 5/10
    4 / -1

    The circuit shown in the figure contains two diodes each with a forward resistance of 50 ohms and with infinite backward resistance. If the battery voltage is 6V, the current through the 100 ohm resistance (in  amperes) is

    Solutions

    In the circuit, diode D1 is forward biased, while D2 is reverse biased. Therefore, current i (through D1 and 100Ω resistance) will be

    Here, 50Ω is the resistance of D1 in forward biasing.

  • Question 6/10
    4 / -1

    Which of the following statements is not true?

    Solutions

    In n-type semiconductors, electrons are the majority charge carriers.

  • Question 7/10
    4 / -1

    The maximum kinetic energy of photoelectrons emitted from a surface when photons of energy 6 eV fall on it is 4 eV. The stopping potential, in volt, is

    Solutions

    Stopping potential is the negative potential applied to stop the electrons having maximum kinetic energy.
    Therefore, stopping potential will be 4 volt.

  • Question 8/10
    4 / -1

    In hydrogen spectrum the wavelength of Hα line is  656 nm, whereas in the spectrum  of a distant galaxy, Hα line wavelength is 706 nm. Estimated speed of the galaxy with respect to earth is,

    Solutions

    KEY CONCEPT : According to Doppler’s effect of light, the wavelength shift is given by

  • Question 9/10
    4 / -1

    A particle of mass M at rest decays into two particles of masses m1 and m2, having non-zero velocities. The ratio of the de Broglie wavelengths of the particles, λ1/λ2, is

    Solutions

    Applying conservation of linear momentum, Initial momentum = Final momentum

    0 = m1v1 – m2v2 ⇒ m1v1 = m2v2

  • Question 10/10
    4 / -1

    Which of the following is a correct statement?

    Solutions

    Beta rays are same as cathode rays as both are stream of electrons.

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