CLASS-VIII

COMBUSTION

Q1. Fill in the blanks:

            a )    Fuel must be heated to its______________________ before it starts burning.

            b)     Fire produced by oil cannot be controlled by ________________.

            c)      ______________ is essential for combustion.

            d)     Fuel efficiency is expressed in units ___________.

            e)      ________________ fuels have highest calorific value.

            f)      Incomplete combustion of carbon produces __________________________ gas.

            g)     Complete combustion of carbon produces ___________________________ gas.

            h)      ___________________________ is the coldest part of the flame.

            i)       Luminous zone is _______________ in colour.

            j)       _________ phosphorous is present in matchstick.

Q2. What are inflammable substances? Give example.

Q3. Name 4 types of combustion. Give one example of each.

Q4. Differentiate between rapid and spontaneous combustion.

Q5. Name the unit in which the calorific value of a fuel is expressed.

Q6. Explain how CO₂  is able to control fires.

Q7. Which substances on burning give a flame?

Q8. Camphor burns with a flame, but charcoal glows. Why?

Q9. Which zone of a flame does a goldsmith use for melting gold and silver and why?

Q10. What is the basic principle in controlling fire?

Q11. Give reasons:

                i)   Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

               ii)   It is difficult to burn a heap of green leaves but dry leaves catch fire easily.

Q12. 1kg of LPG produces 55000 kJ of energy. What is the calorific value of LPG?

Q13. In an experiment 4.5kg of a fuel was completely burnt. The heat produced was measured to be 1,80,000 kJ. Calculate the calorific value of the fuel.

Q14. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?

HUMAN EYE

CLASS-VIII

THE HUMAN EYE

Q1. Name the outermost part of human eye.

Q2. Name the part of human eye which acts as a screen to obtain the image of an object.

Q3. Name two common defects of vision.

Q4. A child wears spectacles fitted with concave lenses. Name the defect of vision.

Q5. When we enter a dim-lit room from a bright light, we are not able to see the object in the room for some time. Explain, why?

Q6. Why do we have two eyes instead of one eye?

Q7. A child has difficulty in reading the black board while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?

Q8. What is the function of iris in the eye?

Q9. a) Which muscle controls the focal length of the eye lens?

       b) Which nerve sends the image to the brain?

Q10. Which phenomena is used in cinematography?

Q11. What happens to the image distance in the eye when we increase the distance of an object from the eye?

Q12. What type of lens is an eye lens?

Q13. Why does a person suffering from hypermetropia prefers to remove his spectacles while looking at distant objects? Explain.

Q14. Why do chickens wake up early and sleep early?

Q15. Visit an eye surgeon of your locality. Find out the following facts:

a)     Which part of our eye is donated at the time of eye donation?

b)    For how long the donated eye can be preserved?

c)     Who can’t donate his eyes?