Pollution of Water

CLASS-VIII

ASSIGNMENT-5

POLLUTION OF WATER

Q1. Define water pollution.

Q2. Give 2 purposes of purification.

Q3. Water should be preferably boiled before consumption. Why?

Q4. Hot water can also be a pollutant. Comment.

Q5. Mention any 4 ways by which you can recognize water pollutants.

Q6. How is water pollution responsible for depletion of oxygen in water?

Q7. Name any three water-borne diseases.

Q8. Name any 2 chemicals used in purification of water.

Combustion

CLASS-VIII

COMBUSTION

ASSIGNMENT-4

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?

ANSWERS OF ASSIGNMENT-3

HUMAN EYE

CLASS-VIII

A1. Cornea

A2. Retina

A3. i) Myopia   ii) Hypermetropia

A4. Myopia

A5. In a bright light, the iris contracts the pupil of an eye to allow less light to enter the eye. When we enter the dim-lit room, iris takes some time to expand the pupil of an eye to allow more light to enter the eye so that image of the object forms on retina.

A6. Two eyes are better than one eye because the field of view with two eyes is more than with one eye.

A7. Myopia. This defect can be corrected by using a concave lens.

A8. Iris controls the amount of light entering the eye by controlling the size of the pupil and is also responsible for the colour of the eye.

A9. a) Ciliary muscle

       b) Optic nerve

A10. Persistence of vision

A11. It remains unchanged because the image distance in the eye is fixed as it is the distance between the eye lens and the retina.

A12. Convex lens

A13. A hypermetropic eye can have normal far point. If he uses spectacles of converging lens, he will have more converging power than needed and the distant object may get focused in front of the retina. As a result, the distant objects will appear blurred.

A14. Chickens have very few rod cells and therefore cannot differentiate in dim light.

A15. a) Cornea

 b) After eye tissue is recovered, the technician carefully places it in a special container, where it is submerged in a chemical preservation solution to keep it healthy during transport, storage and laboratory evaluation. If stored properly and refrigerated, corneas can be preserved for as long as 14 days after their recovery, though most are usually used much quicker.

 c) Death due to unknown causes. People who die due to infections such as rabies, syphilis, infectious hepatitis and AIDS, cannot donate.

Human Eye

CLASS-VIII

THE HUMAN EYE

ASSIGNMENT-3

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?

refraction n dispersion of light

REFRACTION AND DISPERSION OF LIGHT

ASSIGNMENT-2

CLASS-VIII

Q1. Who discovered that sunlight consists of 7 colours?

Q2. Why sunlight reaches us (earth) in the form of white light and not as its components?           

Q3. A laser beam consists of light of only single colour. Will a laser beam incident on a glass prism produce a spectrum?

Q4. A glass slab doesn’t show dispersion. Why?

Q5. A rainbow is seen in the sky after rainfall. Why?

Q6. Name the lens which has a virtual focus.

Q7. How many focus points does a concave or a convex lens have?

Q8. Name the lens which always forms a virtual and erect image, no matter where the object is placed.

Q9. Name the phenomenon on which working of lens is based.

Q10. What is the difference between a convex lens and a concave lens?

Q11. Which lens is present in the eye-- concave or convex?

Q12. The image of a candle is formed by a convex lens. If the lower half of the lens is covered with a black paper, will still the full image of the candle be formed on the screen? Explain by drawing a suitable ray diagram.

Q13. When a magnifying glass focuses the sun’s rays on a sheet of paper, it starts burning. Why?

Q14. Which of the following would you prefer to read very small letters printed on the pages of a dictionary?

i)                   A convex lens of focal length 100cm

ii)                 A concave lens of focal length 10cm

iii)               A concave lens of focal length 5cm

iv)               A convex lens of focal length 5cm

Q15. You are given a convex lens and a black paper. A teacher asks you to burn the paper in sunlight. Draw the ray diagram to show that paper burns in sunlight.

LIGHT

LIGHT

CLASS-VII

ASSIGNMENT-1

Q1. The focal length of a spherical mirror is 10cm. What is the radius of curvature of this spherical mirror?

Q2. Name a mirror that gives an erect and magnified (enlarged) image of an object.

Q3. Where should an object be placed on the principal axis of a concave mirror so that its real image is of the same size as that of the object?

Q4. Name the rear-view mirror used in vehicles.

Q5. No matter how far you stand from a mirror, your image appears erect. The mirror is:

i)                   plane

ii)                 convex

iii)               concave

iv)               either plane or convex

Q6. Name the type of mirror which always forms a virtual and diminished image.

Q7. A man standing in front of a magical mirror, finds his image having a very small head, a fat body and legs of normal (same) size. What type of mirrors are used in this magical mirror?

Q8. Differentiate between virtual image of a concave mirror and of a convex mirror.

Q9. The angle between the incident ray and the mirror is 40.

i)                   What is the angle of incidence?

ii)                 What is the angle of reflection?

Q10. Explain lateral inversion.

Q11. How can you distinguish between a plane mirror, a concave mirror and a convex mirror without touching them?

Q12. The minimum distance between an object and its real image formed by a concave mirror is _________.