Question

Science practical class 10 practical number 3,4,5,6 hurry up!

Answer 1

3. Write two precautions to be taken while identifying different parts of an embryo of a dicot seed.

Answer.

(i) The slide should be properly focused.

(ii) Slide should be observed first under low-power magnification and then under high-power magnification of the compound microscope.

4. A student is to conduct an experiment to show CO2 is released during respiration. List two precautions that he/she must take for obtaining correct observation.

Answer.

Two precautions to be taken are:

(i) Germinating seeds (living) should be used.

(ii) The experiment set up must be air-tight.

5. A student focuses the image of a candle flame, placed at about 2 m from a convex lens of focal length 10 cm, on a screen. After that he moves gradually the flame towards the lens and each time focuses its image on the screen.

(a) In which direction does he move the lens to focus the flame on the screen?

(b) What happens to the size of the image of the flame formed on the screen?

(c) What difference is seen in the intensity (brightness) of the image of the flame on the screen?

(d) What is seen on the screen when the flame is very close (at about 5 cm) to the lens?

Answer.

(a) The student moves the lens away from the screen to focus the image because on moving the candle towards the lens, the image distance increases.

(b)The size of the image increases when the object is moved towards the lens.

(c) Intensity of the image decreases.

(d) When the candle is moved very close to the lens, no image is formed on the screen. A virtual image is formed behind the candle on the same side of the screen.

6. A student dropped few pieces of marble in dilute hydrochloric acid contained in a test tube. The evolved gas was then passed through lime water. What change would be observed in lime water? Write balanced chemical equation for both the change observed?

Answer.

When dilute HCl is added to marble which is calcium carbonate, it forms calcium chloride, water and carbon dioxide. The chemical equation for the reaction is as follows:

                                    CaCO3 + 2HCl → CaCl2 + H2O + CO2

Carbon dioxide gas turns lime water milky due to the formation of calcium carbonate.

The chemical equation showing the reaction between lime water and carbon dioxide is as follows:

                                      Ca(OH)2 + CO2 → CaCO3 + H2O

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