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Physics Test - 1
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Physics Test - 1
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  • Question 1/10
    1 / -0

    If in the following figure, the height of the object is H1=+2.5 cm, then the height of image H2 formed is:

    Solutions

    By concave mirror formula,

    1f=1v+1u

    Here u=1.5f,f=f

    We have,

     1(f)=1v+1(1.5f)

    1v=13f or v=3f

    Now, magnification in mirror is given by,

    m=IO=vu

    Where I is size of image and O is size of object.

    Here O=+2.5 cm

    I2.5=3f(1.5f) or I=5 cm

  • Question 2/10
    1 / -0

    If the force on a moving body is always uniform and perpendicular to its motion, then:

    Solutions

    If the force on a moving body is always uniform and perpendicular to its motion, then speed remains the same, but direction changes.

    From the definition of the centripetal force, if a force is perpendicular to the motion, it is a centripetal force and this force makes the body move in a circular motion.

    We know the centripetal force acting on a body of mass 'm' revolving with radius 'r' is:

    F=mv2r

    Since F is uniform, so v will also be uniform. So speed (magnitude of velocity) will not change.

    In a circular motion, a body moves in a circle, and in a circle the direction of motion changes at every point.

    • At point A, the direction of the velocity is in the upward direction.
    • At point B, the direction of the velocity is in the leftward direction.
    • At point C, the direction of the velocity is in the downward direction.

    The body comes in the initial direction after one complete circle. So, if the force on a moving body is always uniform and perpendicular to its motion, then Speed remains the same, but direction changes.

  • Question 3/10
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    The bob of a simple pendulum is a spherical hollow ball filled with water. A plugged hole near the bottom of the oscillating bob gets suddenly unplugged. During observation, till water is coming out, the time period of oscillation would

    Solutions

    When water begins to come out, the centre of mass begins to lower. There is an increase in the effective length and hence an increase in the time period : When water flows out completely, the centre of mass begins to shift back to the geometrical centre of the follow bob. So, there is a decrease in the effective length and hence a decrease in time period. When water flows out completely, the centre of mass is again at the geometrical centre. Now, the time period is the same as in the beginning.

  • Question 4/10
    1 / -0

    One kilowatt-hour is unit of:

    Solutions

    The kilowatt-hour (SI symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy equal to 3600 kilojoules (3.6 megajoules). The kilowatt-hour is commonly used as a billing unit for energy delivered to consumers by electric utilities.

    Hence the correct option is (A).

  • Question 5/10
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    When an object is heated, the molecules of that object:

    Solutions

    When heat is added to a substance the molecules in it start moving faster. The space between them increases thus expanding and taking up space. As atoms move faster, the space between atoms increases. The motion and spacing of the particles determine the state of matter of the substance. The end result of increased molecular motion is that the object expands and takes up more space.

  • Question 6/10
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    A Carnot engine works as a refrigerator between 250 K and 300 K. If it receives 750 calories of heat from the reservoir at the lower temperature, then the amount of heat rejected at the higher temperature is

    Solutions

  • Question 7/10
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    F1 and F2 are focal lengths of the objective and the eyepiece of a telescope, respectively. The angular magnification for this telescope is equal to

    Solutions

    Angular magnification is the ratio of the focal length of the objective to the focal length of the eyepiece. 

  • Question 8/10
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    An observer is moving towards a stationary source with 1/10 the speed of sound. The ratio of apparent frequency to real frequency is

    Solutions

    Frequency as observed by the observer is 

  • Question 9/10
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    The disc of a siren containing 60 holes rotates at a constant speed of 360 rpm. The emitted sound is in unison with a tuning fork of frequency

    Solutions

    The number of holes in the disc determines the number of the waves produced on each rotation. The total number of waves emitted per second is the frequency,

  • Question 10/10
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    A police car horn emits sound at a frequency of 240 Hz when the car is at rest. If the speed of sound is 330 m/s, the frequency heard by an observer who is approaching the car at a speed of 11 m/s, is

    Solutions

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