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CBSE Class 9 Science Exam 2018: Important Practical Based Questions

Feb 8, 2018 17:31 IST
    CBSE Class 9 Science Important Practical Based Questions
    CBSE Class 9 Science Important Practical Based Questions

    Here we are providing a set of important practical based questions to be prepared for CBSE class 9 Science annual exam 2018. From this year, i.e., 2018 onwards, class 9 Science paper will have a separate section for practical based questions.

    Section- B will comprise practical based questions only. There will a total of six questions carrying 2 marks each.

    Given below is a collection of important questions based on practical skills to prepare for CBSE class 9 Science exam:

    1. Mention the two precautions to determine the boiling point of water in laboratory.

    Answer.

    (i) The position of bulb should be slightly above the water level.

    (ii) Stir the water continuously in beaker so that temperature should remain constant

    2. The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?

    Answer.

    Number of vibrations produced in 1s = 100

    Number of vibrations produced in 60 sec = 100 × 60 = 6000

    Now, 1 minute = 60 seconds

    Thus, number of vibrations produced in one minute = 6000

    CBSE Class 9 Science Exam 2018: Important Long Answer Type Questions

    3. In which of the two, glycerine or kerosene, the loss in weight of a solid when fully immersed in them will be more and why ?

    Answer.

    Density of glycerine is more than that of kerosene.

    A liquid having higher density exerts more upthrust force on object than other liquid having low density. Thus, greater the density of a liquid, the more will be the the buoyant force exerted on the object immersed in it.  Now, due to this greater upthrust (buyont force), the object experiences greater apparent weight loss.

    Thus in case of glycerine, the loss in weight of a solid when fully immersed in it will be more than when immersed in kerosene.

    4. A sound wave travels at a speed of 340m/s. If its wavelength is 2 cm, what is the frequency of the wave? Will it be in the audible range?

    Answer.

    It is given that,

    Velocity of sound, v = 340 m/s

    Wavelength, λ = 1.4 m

    Frequency, ν =?

    We know that, speed = wavelength × frequency

    ⟹          340 = 1.4 x ν
    ⟹              ν = 340/1.4 = 242.86 Hz
    As the audible range is between 20 Hz – 20,000 Hz
    Here, 242.86 Hz < 20,000 Hz
    Therefore it is in the audible range.

    5. When dipped in a fluid, name the factor on which the loss in weight of a solid depends. Name the two forces which act upon the solid dipped in the fluid.

    Answer.

    Loss in weight of a solid dipped in a fluid depends upon the density of that fluid.
    The two forces which act upon the solid dipped in the fluid are:

    • True weight of the body acting vertically downwards.
    • Buoyant force or upward thrust acting vertically upwards.

    6. In an experiment to determine the boiling point of water, state reason for the following:

    (i) Pumice stone pieces are added to water in the beaker.

    (ii) A glass stirrer is used.

    Answer.

    (i) Pumice stone is added to avoid any bumping of water. When the temperature is raised for boiling the water, it starts to bump. But pumice stone being porous, provides space for air. This reduces bubbling in hot water to facilitate the boiling process.

    (ii) A glass stirrer is used to ensure uniform heating of water.

    7. A mixture of sand, powdered glass and common salt is dissolved in water and then filtered. Name the substance left on filter paper. Name the substance in the filtrate.

    Answer.

    Out of the given three substances only common salt is soluble in water whereas both sand and powdered glass are insoluble in water. Thus when a mixture of sand, powdered glass and common salt is dissolved in water and then filtered sand and powdered glass would be left on filter paper while common salt will be present in the filtrate. 

    8. A free falling object eventually stops on reaching the ground. What happens to its kinetic energy?

    Answer.

    Its kinetic energy will be zero on reaching the ground. Actually, when an object falls freely towards the ground, its potential energy decreases and kinetic energy increases. But as soon as the object touches the ground, all its potential energy gets converted into kinetic energy and finally when the ball stops after hitting the ground, all its kinetic energy gets converted into heat energy and sound energy. 

    9. Name the adaptation of fish which helps it in each of the following:

    (i) Swimming in water

    (ii) Breathing

    Answer.

    (i) Fish have fins for swimming in water.
    (ii) They have gills for breathing in water.

    CBSE Class 9 Science Exam 2018: Important Very Short Answer Type Questions

    10. A baby is not able to tell her/his caretakers that she/he is sick. What would help us to find out that the baby is sick?

    Answer.

    Behavioural changes like constant crying, irritabilty, improper intake of food, low period of activeness and mood swings can help to determine that the baby is sick.

    11. List any two precautions you must take while finding the melting point of ice and boiling point of water.

    Answer.

    (i)  The bulb of the thermometer should be completely inside the crushed ice.

    (ii) The thermometer should not touch the wall of the beaker.

    12. When a body hanging with the hook of a spring balance is immersed in a liquid, state the factor due to which the reading of spring balance decreases. Define the factor.

    Answer.

    The factor due to which the reading of spring balance immersed in a liquid decreases is buoyant force or upthrust.

    Buoyant force (upthrust) is the upward force exerted by any fluid upon a body immersed in it.

    13. A student recorded the mass of dry raisins as 2.0 g and mass of raisins after soaking as 3.5 g. Calculate the percentage of water absorbed by raisins. Write one precaution for this experiment.

    Answer.

    Mass of dry raisins = 2.0 g

    Mass of raisins after soaking = 3.5 g

    Mass of water absorbed = 3.5 – 2.0 = 1.5 g

    Precaution: 
    Raisins should be well immersed in water instead of lying not on surface.

    14. Mention two features adopted by birds which help them to fly.

    Answer.

    Two features adopted by birds which help them to fly are:

    • Streamlined body shape which helps them to cut the air flow.
    • Light bones reduce their overall body weight to help in easy flight.

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