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Physics Test 253

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Physics Test 253
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Weekly Quiz Competition
  • Question 1
    4 / -1

    Two radioactive substances A and B have decay constants 5λ and λ, respectively. At t = 0, a sample has the same number of the two nuclei. The time taken for the ratio of the number of nuclei to become (1/e)2 will be:

    Solution

     

  • Question 2
    4 / -1

    The magnetic field and number of turns of the coil of an electric generator is doubled then the magnetic flux of the coil will:

    Solution

    Given: N = 2N1 and B = 2B1

    The magnetic flux through the electric generator when the magnetic field is B, the Area is A, and the number of turns is N

    φ = N B A cos θ ....(1)

    The magnetic flux through the electric generator when the magnetic field and the number of turns of the coil of an electric generator is doubled

    φ1 = N1 B1 A cosθ   ...(2)

    ⇒ φ1 = (2N)(2B) A cos θ = 4 N B A cos θ = 4φ [∵φ = NBA cos θ]

     

  • Question 3
    4 / -1

    The frequency f of vibrations of a mass m suspended from a spring of spring consant k is given by f = Cmxky, where C is a dimensionless constant. The values of x and y are, respectively

    Solution

     

  • Question 4
    4 / -1

    Three forces are acting on a particle of mass m initially in equilibrium. If the first 2 forces (R1 and R2) are perpendicular to each other and suddenly the third force (R3) is removed, then the acceleration of the particle is

    Solution

    Three forces are acting on a particle of mass m initially in equilibrium. If the first two forces R1 and R2 perpendicular to each other, R3 has to balance the resultant of the other two forces. So,

    Now, the force R3 is removed

    So, the particle moves with the resultant force R1 and R2

    Now, the acceleration is

    R3 = ma

    a = R3/m

    Hence, the acceleration of the particle is R3/m.

     

  • Question 5
    4 / -1

    The distance x moved by a body of mass 0.5 kg by a force varies with time t as x = 3t2 + 4t + 5 where x is expressed in metre and t in second. What is the work done by the force in the first 2 seconds?

    Solution

     

  • Question 6
    4 / -1

    Frequency of a particle executing SHM is 10 Hz. The particle is suspended from a vertical spring. At the highest point of its oscillation the spring is unstretched Maximum speed of the particle is (g = 10 m/s2)

    Solution

    Mean position of the particle is mg/k distance below the unstretched position of spring. Therefore, amplitude of oscillation is A = mg/k

     

  • Question 7
    4 / -1

    If λ1 and λ2  are the wavelengths of the first members of Lyman and Paschen series, respectively, then λ1 : λ2 is:

    Solution

     

  • Question 8
    4 / -1

    Three rods of Copper, Brass and Steel are welded together to from a Y –shaped structure. Area of cross – section of each rod = 4 cm2. End of copper rod is maintained at 100°C where as ends of brass and steel are kept at 0°C. Lengths of the copper, brass and steel rods are 46, 13 and 12 cms respectively. The rods are thermally insulated from surroundings except at ends. Thermal conductivities of copper, brass and steel are 0.92, 0.26 and 0.12 CGS units respectively. Rate of heat flow through copper rod is

    Solution

     

  • Question 9
    4 / -1

    In an experiment for determination of refractive index of glass of a prism by i – δ plot, it was found that a ray incident at an angle of 35° suffers a deviation of 40° and that it emerges at an angle of 79°. In that case, which of the following is closest to the maximum possible value of the refractive index?

    Solution

     

  • Question 10
    4 / -1

    In an electron microscope, the resolution that can be achieved is of the order of the wavelength of electrons used. To resolve a width of 7.5 × 10-12 m, the minimum electron energy required is close to:

    Solution

     

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