Model-2 Test Papers Class 8 Science
Model Test Paper 2
Fill in the blanks. (1×10 = 10)
- Rolling friction is less than sliding friction.
- The S.I. unit of pressure is Pascal.
- Friction can be reduced by lubrication.
- S.I. unit of the time period is hertz.
- The flow of electrons is called an electric current.
- The loud sound produced during lightning is called thunder.
- The angle of incidence equals the angle of reflection.
- When white light passes through a prism it is deflected.
- The Ursa Major constellation has seven prominent stars.
10.Water Pollution causes excessive growth of algae in water bodies.
Match the following. (0.5 × 10 = 5)
Column A Column B
- Comet (a) 20 Hz – 20,000Hz
- Drug (b) repel
- Cataract (c) force
- Push or pull (d) amplitude
- Benjamin Franklin (e) pharma dynamics
- Loudness (f) number of cycle per second
- Bird (g) lightning conductor
- Frequency (h) has a bright head and long tail
- Audible range (i) cloudy areas in the lens of the eye
- Like charges (j) streamlined body
- h 2.e 3.i 4.c 5.g 6.d 7.j 8.f 9.a 10.b
Answer the following in one sentence: (1×5 = 5)
Q1. Why is friction called a ‘necessary evil’?
Ans. Friction is necessary for many applications to prevent slipping or sliding. But also, it can be a nuisance because it can hinder motion. A good compromise is necessary to get just enough friction or a proper combination of frictions. We cannot walk, write and drive, without, friction. In certain cases like the motion of machines, wear and tear of machines, loss of energy friction is an ‘evil’.
Q2. Name few greenhouse gases.
Ans. Water vapour (H2O), carbon dioxide (CO2), methane
Q3. What type of sounds can a bat detect?
Ans. Bats can hear frequencies up to 100 kHz. They can detect ultrasonic sounds.
Q4. Why is CNG called as cleaner fuel?
Ans. CNG is called as cleaner fuel because it pollutes less than the other fossil fuel and emission of co2 is less compared to other fuels.
Q5. Define pollution and pollutant.
Ans. Pollution is defined as the presence of impurities or pollutant substances in sufficient concentration levels, causing harmful effects on human beings, animals, plant life or material resources when exposed for a sufficient duration of time, thus reducing the quality of life in the environment. Any substance that causes pollution is called pollutant.
Short answer questions: (1×5 = 5)
Q1. How is acid rain formed?
Ans. Acid rain is caused by a chemical reaction that begins when compounds like sulphur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.
Q2. Why is it difficult to observe the planet, Mercury?
Ans. It is difficult to observe the planet Mercury because Mercury is the closest planet to the sun and the smallest planet in the solar system. Mercury has no natural satellite. Sun-scorched Mercury is only slightly larger than the earth’s moon.
Q3. What is hypermetropia? How can it be corrected?
Farsighted individuals typically develop a problem of reading up close before the age of 40. The farsighted eye is usually slightly shorter than a normal eye and may have a flattened cornea. Thus, the light of distant objects focuses behind the retina unless the natural lens can compensate fully. Near objects require even greater focusing power to be seen clearly and therefore, blue red more easily. Hypermetropia can be corrected by using a convex lens.
Q4. How can you protect yourself from lightning?
When a thunderstorm threatens, get inside a home or large buildings.
- If inside a home, avoid using the telephone except for emergencies.
- If outside, within no time reach to a safe building or an automobile.
- Do not stand underneath a natural lightning rod such as a tall, isolated tree.
- Get out of and stay away from open water.
- Get away from tractors and other metal farm equipment.
- Stay away from wire fences, cloth lines, metal pipes, rails and other metallic paths which could carry lightning to you from some distance away.
- In a forest, seek shelter in a low area under a thick growth of small trees. Be alert for flash floods.
Q5. How can liquids be tested for conduction of electricity?
Ans. To test whether a liquid conducts electricity or not.
Dry cell, water in a container, connecting wires and bulb.
Take a dry cell, connecting wires and electric bulb. Connect the electric bulb
and dry cell with connecting wires. Take a container & fill it about half with distilled water. Distilled water is pure water. Dip the open ends of conducting wires in water (as shown in fig.) What do you observe?
Repeat the activity with tap water.
The bulb does not light up because pure water is a bad conductor of electricity. If you test it with simple tap water, a bulb will light up. It is because of dissolved salts in tap water.
Answer the following questions in 50-60 words: (3×5 = 15)
Q1. What are the advantages of electroplating?
Ans. Electroplating is used to coat a surface with a thin layer of metal through electrochemical processes. It is widely used in various industries for coating metal objects with the thin layer of a different metal. The layer of metal deposited has some desired properties, which the metal of the object lacks. For example, chromium plating is done on many objects such as car parts, bath taps, kitchen gas burners, wheel rims and many others for the fact that chromium is corrosion resistant, and thus prolongs the life of the parts.
Electroplating has wide usage in industries. It is also used in making inexpensive jewellery. Electroplating increases the life of the metal and prevents corrosion.
Q2. Write an activity to show that rolling friction is less than sliding friction.
Ans. To Show that rolling friction is less than sliding friction:
Place a book on a table. Apply a force so that this book starts sliding. Now place the pencils under the book as shown in the figure. Now apply force to move the book. You will find the force applied now to roll the book is less than the force to make the book slide over the given surface.
Q3. Write different ways by which noise pollution can be controlled.
Ans.(i) Use of horns with loud sounds, motorbikes with damaged exhaust pipes, noisy trucks should be banned.
(ii) Noise producing industries, airports, bus and transport terminals and railway stations to be located far from residential areas.
(iii) Community law enforcers should check the misuse of loudspeakers, processions, outdoor parties and discos, as well as public announcement systems. Community laws must create silence zones near schools/ colleges, hospitals,
(iv) Vegetation (trees) along roads and in residential areas is a good way to reduce noise pollution as they absorb sound.
Q4. What are sex hormones? How is a father responsible for deciding the sex of the baby?
Ans. Human beings have 23 pairs of chromosomes. Out of these, twenty-two (22) autosomes are identical in both females and males while the sex chromosomes are different. The sex chromosomes in females are a pair of X-chromosomes while those in males are an X-chromosome and Y-chromosome. The sex-determining chromosomes are called sex chromosomes.
The father is responsible for the sex of an unborn child. Human beings have 23 pairs of chromosomes. Out of these, twenty-two (22) autosomes are identical in both females and males while the sex chromosomes are different. The sex chromosomes in females are a pair of X-chromosomes while those in males are an X-chromosome and Y-chromosome. Of the total sperms produced during spermatogenesis, 50% carry X-chromosomes while the remaining 50% carry Y-chromosomes, the sex of the offspring is determined by the genetic makeup of the sperm. Whether a baby is going to be a girl or a boy depends on upon which sperm fertilises ovum. If the sperm carrying X chromosome fertilises the egg then the female child is born. If the sperm carrying Y chromosome fertilises the egg, then the male child will be born.
Q5. Why do the trucks and buses have broader wheels than the wheels of scooters or cycles?
Ans. Trucks and buses have broader wheels than the wheels of scooters or cycles because so that it reduces pressure and the tyres don’t burst.
Draw diagram for each of the following. (1.5×2 = 3)
- Human Ear
- Endocrine glands in human
One Word Answers: (1×7 = 7)
- The maximum increase in height takes place during:
- Which of the following gland secretes oil?
- A charged balloon attaches to a wall because of ………………….. force
- Sound waves do not travel through ……………………..
- Carbon rods, used as electrodes are made up of ………………………..
- Movement of the tectonic plates leads to ………………………