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ICSE-X-Physics

Previous Year Paper year:2017

with Solutions - page 2

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  • #2-d-ii
    velocity of light in vacuum or air and the velocity of light in a given medium?
    Ans : Refractive index is the ratio of the velocity of light in vacuum to the
    velocity of light in a medium.
    ``\mu = \frac{c}{v}``
  • #2-e [2]
    State the conditions required for total internal reflection of light to take place.
    Ans : Conditions necessary for total internal reflection to take place are
    (i) Light must travel from a denser medium to a rarer medium.
    (ii) Angle of incidence must be greater than the critical angle for the pair of media
  • #3
  • #3-a [2]
    Draw a ray diagram to show the refraction of a monochromatic ray through a prism when it suffers minimum deviation.
    Ans : Refraction of a monochromatic ray through a prism when it goes through
    minimum deviation:
  • #3-b [2]
    The human ear can detect continuous sounds in the frequency range from ``\pu{20 Hz}`` to ``\pu{20,000 Hz}``. Assuming that the speed of sound in air is ``\pu{330 ms-1}`` for all frequencies; calculate the wavelengths corresponding to the given extreme frequencies of the audible range.
    Ans : Audible range of hearing for a normal human ear is 20 Hz to 20,000 Hz.
    Speed of sound in air, v = 330 m/s
    Speed, wavelength and frequency are related as
    $$v=\nu\lambda$$
    $$\lambda =\frac{v}{\nu}$$
    $$\nu_{lower} = \pu{20 Hz};$$
    $$\lambda_{lower} = \frac{330}{20) = 16.5 m$$
    similarly
    ``\nu_{higher} = \pu{20 Hz};``
    $$\lambda_{higher} = \frac{330}{20000} (*1000)= 16.5 mm$$
  • #3-c [2]
    An enemy plane is at a distance of 300 km from a radar. In how much time the
    radar will be able to detect the plane? Take velocity of radio waves as ``\pu{3E8 ms-1}``.
    Ans : Distance between the plane and the radar:
    d = 300 km = ``\pu{300E3 m} = \pu{3E5 m }``
    Velocity of radio waves, c = ``\pu{3E8 ms^-1}``
    Since Waves from the radar will travel to the plane(d) and
    then reflect and travel backto the receiver of the radar(d). Hence,
    the total distance travelled by the waves = 2d .
    $$2d = c*t$$
    $$2d/c = t$$
    $$t = \frac{2*\pu{3E5}}{\pu{3E8}}$$
    $$t = \pu{2E-3} * 1000 = \pu{2ms}$$
  • #3-d [2]
    How is the frequency of a stretched string related to:
  • #3-d-i
    it’s length?
    Ans : Frequency of a stretched string is inversely proportional to its length.
    $$f \propto \frac{1}{L}$$
  • #3-d-ii
    it’s tension?
    Ans : Frequency of a stretched string is directly proportional to the square root
    of the tension in the string.
    $$f \propto \sqrt T$$
  • #3-e [2]
    Define specific resistance and state its SI unit.
    Ans : Specific resistance or resistivity of a material is the resistance of a wire of
    that material of unit length and unit area of cross-section.
    Its SI unit is ``\pu{ohm metre (\Omega m)}``.
  • #4
  • #4-a [2]
    An electric bulb of ``\pu{300 \Omega}`` draws a current of ``\pu{0.4 A}``. Calculate the power of the bulb and the potential difference at its ends.
    Ans : Current drawn by the bulb, I = 0.4 A
    Resistance of the bulb, R = 300 ``\Omega``
    Power of the bulb is:
    ``p= i^2r``
    so, ``P = (0.4)^2 * 300 = 48 W``
    Potential difference at the ends of the bulb is
    V = IR
    V= 0.4 * 300 = 120 V
  • #4-b [2]
    State two causes of energy loss in a transformer.
    Ans : Causes of energy loss in a transformer:
    (i) Eddy currents developed in the core.
    (ii) Hysteresis loss because of repeated magnetisation and demagnetisation
    of the iron core.
  • #4-c [2]
    State two characteristics of a good thermion emitter.
    Ans : Characteristics of a good thermion emitter:
    (i) The work function of the substance should be low so that electrons may be emitted from it even when it is not heated to a high temperature.
    (ii) The melting point of the substance should be high so that it may not melt
    when it is heated to the temperature required for thermionic emission.
  • #4-d [2]
    State two factors upon which the rate of emission of thermions depends.
    Ans : Factors on which the rate of emission of thermions depend:
    (i) Nature of the metal surface: Lower the work function of the metal,
    greater is the rate of emission of electrons.
    (ii) Temperature of the surface: Higher the temperature of the surface, greater is the rate of emission of electrons.
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