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Page No 263:

Question A.1:

Liquids and gases are together called
(a) materials
(b) fluids
(c) group gases
(d) none of these

Answer:

(b) Fluids

Liquids and gases are together called fluids.

Page No 263:

Question 1:

Fill in the blanks with the correct words.
1. .................... (Gravitational/Electrostatic) force makes the Earth move around the sun and also makes the moon go around the Earth.
2. Atmospheric pressure is measured using an instrument called the .................... (barometer/biometer).
3. Objects that produce sound are called .................... (voice/sonorous).
4. Burning of fossil fuels like coal and petroleum in thermal power plants releases .................... (carbon dioxide/sulphur dioxide) and nitrogen.
5. The distance travelled by light in one year is called a .................... (satellite/light year).

Answer:

1. Gravitational force makes the Earth move around the sun and also makes the moon go around the Earth.

2. Atmospheric pressure is measured using an instrument called the barometer.

3. Objects that produce sound are called sonorous.

4. Burning of fossil fuels like coal and petroleum in thermal power plants releases sulphur dioxide and nitrogen.

5. The distance travelled by light in one year is called a light year.

Page No 263:

Question 2:

Write T for the true statement and F for the false one. Correct the false statement(s).
1. Mars is the largest planet in the solar system.
2. Richard scale is used to measure the magnitude of an earthquake.
3. The positively charged particles in an atom are called protons.
4. Ions are atoms or group of atoms with a positive or a negative charge.
5. The number of oscillation per second is called the frequency of oscillations.

Answer:

1.F Jupiter is the largest planet in the solar system.
2.F Richter scale is used to measure the magnitude of an earthquake.
3.T
4.T
5.T

Page No 263:

Question 1:

Fill in the blanks with the correct words.
1. .................... (Friction/Pressure) is defined as the force per unit area.
2. The sound produced is controlled by .................... (larynx/vocal cord).
3. .................... (Anode/Cathode) is the object to be used for coating in electrolysis.
4. 20.95% of the air is made up of .................... (nitrogen/oxygen).
5. .................... (CNG/Diesel) is a less polluting fuel.

Answer:

1. Pressure is defined as the force per unit area.
2. The sound produced is controlled by larynx.
3. Anode is the object to be used for coating in electrolysis.
4. 20.95% of the air is made up of oxygen.
5. CNG is a less polluting fuel.

Page No 263:

Question 2:

Write T for the true statement and F for the false one. Correct the false statement(s).
1. Ground water is obtained from oceans.
2. Water suitable for drinking is called potable water.
3. Large-scale planting of sapling is called deforestation.
4. Pluto is a dwarf planet.
5. A rainbow is an example of dispersion.

Answer:

1.F Ground water is obtained from wells.

2.T

3.F Large - scale planting of sapling is called afforestation

4.T

5.T



Page No 264:

Question A.2:

Unwanted, discomfort-causing sound from any source is called
(a) voice
(b) music
(c) noise
(d) all of these

Answer:

(c) noise

Unwanted discomfort caused by any sound is known as noise.

Page No 264:

Question A.3:

The positively charged ions are called
(a) anions
(b) cations
(c) anode
(d) cathode

Answer:

(b) cations
The positively charged ions are called cations.

Page No 264:

Question A.4:

Atoms that have equal number of positive and negative charges are electrically ....................
(a) charged
(b) discharged
(c) neutral
(d) either (a) or (b)

Answer:

(c) neutral
In an electrically neutral atom, the number of positive and negative charges are equal.

Page No 264:

Question A.5:

The white part of eye is called
(a) pupil
(b) iris
(c) cornea
(d) sclera

Answer:

(d) Sclera

Sclera is the white part of the eye that is filled with a clear watery fluid.

Page No 264:

Question A.6:

This planet is the brightest object in the sky after the moon.
(a) Venus
(b) Earth
(c) Mercury
(d) Pluto

Answer:

(a) Venus

Venus is the planet which is the brightest in the sky after the moon.

Page No 264:

Question A.7:

A very small portion of the moon that becomes visible to us is called
(a) half moon
(b) full moon
(c) crescent moon
(d) either (a) or (b)

Answer:

(c) Crescent Moon

Crescent moon is a very small portion of the moon that becomes visible to us.

Page No 264:

Question A.8:

.................... contains arsenic and mercury.
(a) Wood
(b) Petroleum
(c) Coal
(d) None of these

Answer:

(c) Coal
Coal contains poisonous metals such as arsenic and mercury.

Page No 264:

Question A.9:

This part of the human eye is filled with a clear watery fluid.
(a) Pupil
(b) Retina
(c) Iris
(d) Sclera

Answer:

(d) Sclera

Sclera is the part of the human eye that is filled with a clear watery fluid.

Page No 264:

Question A.10:

The percentage of nitrogen in air is
(a) 20.95%
(b) 0.97%
(c) 0.03%
(d) 78.8%

Answer:

(d) 78.8%

The percentage of nitrogen in air is 78.8%.

Page No 264:

Question A.11:

This planet is visible to the naked eye.
(a) Jupiter
(b) Neptune
(c) Uranus
(d) Mars

Answer:

(d) Mars

Mars is visible to the naked eye. Jupiter can also be seen with the naked eye, but not as easily as Mars. Uranus can also be barely discerned with the naked eye, but only when its at its brightest. Neptune cannot be seen by the naked eye.

Page No 264:

Question A.12:

The part of the .................... that is visible to us is called pinna.
(a) outer ear
(b) middle ear
(c) inner ear
(d) either (b) or (c)

Answer:

(a) outer ear

Pinna is the outer part of the ear that is visible to us.

Page No 264:

Question A.13:

The instrument used to measure pressure is called a
(a) manometer
(b) biometer
(c) pressure gauge
(d) pressure meter

Answer:

(a) Manometer
A manometer uses the height of a column of mercury to find the pressure.

Page No 264:

Question A.14:

Ball bearing is used to .................... friction.
(a) increase
(b) reduce
(c) decrease
(d) change

Answer:

(b) reduce

Ball bearing is used to reduce friction.

Page No 264:

Question A.15:

Skis have .................... area to reduce the pressure on the snow.
(a) large
(b) broad
(c) small
(d) narrow

Answer:

(a) large
Skis have large area to reduce the pressure on the snow.

Page No 264:

Question B:

Write one word for the following.
1. The frictional force offered when sliding an object
2. The rapid back and forth movement of a body a central position
3. This is used to measure seismic waves
4. The angle between the reflected ray and the normal
5. Forces that act on objects by direct of indirect physical contact.

Answer:

1.Sliding friction

2.Vibration

3.Seismograph

4.Angle of reflection

5.Contact force

Page No 264:

Question C:

Write T for the true statement and F for the false one. correct the false statement(s).
1. The presence of chemicals in the air in quantities harmful to human health is known as water pollution.
2. A relatively small body that revolves around a bigger body like a planet is called a celestial body.
3. Mars is the smallest planet in our solar system.
4. Reflection from a rough surface is called regular reflection.
5. Material in which charged particles can move freely is called an insulator.

Answer:

1.F  The presence of chemicals in the air in quantities harmful to human health is known as air pollution.

2.F A relatively small body that revolves around a bigger body like a planet is called a satellite.

3.F Mercury is the smallest planet in our solar system.

4.F Reflection from a rough surface is called diffused reflection.

5.F Material in which charged particles can move freely is called a conductor.



Page No 265:

Question D:

Circle the odd one.

1. Violin Tabla Guitar (Hint: It is not a stringed instrument.)
2. Silver Wood Rubber (Hint: It is a conductor.)
3. Earth Venus Sun (Hint: It is not a planet.)
4. Sun Tree Stars (Hint: It is not a luminous object.)
5. Smoke Loudspeaker TV (Hint: It is not a source of noise pollution.)

Answer:

1.Tabla
2.Silver
3.Sun
4.Tree
5.Smoke

Page No 265:

Question E.1.1:

What is a time period of oscillation? How can it be measured?

Answer:

The time taken to compete one oscillation is called the time period of oscillation. 
It is the inverse of the frequency of oscillation and is measured in seconds (s).

Page No 265:

Question E.1.2:

Define noise and noise pollution.

Answer:

Noise: Noise is an unwanted or unpleasant sound that might cause psychological or physiological disorders.

Noise pollution: The production of the unwanted or unpleasant sound, which disturbs human beings and animals is called noise pollution.

Page No 265:

Question E.1.3:

Give two examples each of conductors and insulators.

Answer:

Conductors are substances that allow the flow of electricity through them.
Examples: Iron and Aluminium

Insulators are the substances that do not allow the flow of electricity through them.
Examples: Rubber and Wood

Page No 265:

Question E.1.4:

Define electrolysis and electroplating.

Answer:

Electrolysis: The method of producing a chemical reaction by passing electric current through liquids containing ions is called electrolysis.

Electroplating:  A process which uses electrolysis to coat one metal with another is called electroplating. The object to be plated  is made the cathode and the metal to be deposited on to the object is made the anode.
 

Page No 265:

Question E.1.5:

Write any two safety measures you can follow to protect yourself during a thunderstorm.

Answer:

 We can protect ourselves from thunderstorms by:
1.Avoiding taking shelter under a tree because, if the lightning strikes the tree, the tree could catch fire and cause severe harm.
2. Taking shelter indoors, or by taking shelter in a car during a thunderstorm.

Page No 265:

Question E.1.6:

Distinguish between incident rays and reflected rays.

Answer:

Sl.No Incident rays Reflected rays
1. Incident rays are the light rays from an object that fall on to the mirror. Reflected rays are the light rays that return or bounce back from the mirror into the same medium in which the incident rays travel.

Page No 265:

Question E.1.7:

Differentiate between Ursa Major and Ursa Minor?

Answer:

Sl.No Ursa Major Ursa Minor
1. Ursa Major is a bright constellation and fairly easy to spot in the night sky. Ursa Minor is a faint constellation and quite difficult to spot in the night sky.
2. A part of this constellation comprising of seven stars,fairly easy to spot is called the Big Dipper or Vrihat Saptarshi. A part of this constellation comprising of seven stars is called Little Dipper or Laghu Saptarshi.
3. Ursa Major is also called the great bear. Ursa Minor is also called the lesser bear.

Page No 265:

Question E.1.8:

Write any two effects of air pollution on plants.

Answer:

Air pollution can have adverse effect on the growth and development of the plants.
The two effects of air pollution on plants are:
1. Photochemical smog, an air pollutant, forms a layer on the leaves and blocks carbon dioxide from being absorbed by the leaves. This leads to a reduction of the photosynthetic activity in plants, thereby curbing its growth.
2. Acid rains which contain sulphuric acid and nitric acid can harm plants' growth and can also cause premature leaf falls.

Page No 265:

Question E.1.9:

Write two main causes of global warming.

Answer:

The two main causes of global warming are:
1.Deforestation.
2.Burning of fossil fuels.

Page No 265:

Question E.1.10:

What is plate tectonics? In how many plates is the Earth divided?

Answer:

The theory that the earth’s lithosphere (outer layer of the earth) is divided into many plates which move with respect to one another due to activities of deeper layers of Earth beneath lithosphere is called the plate tectonics.
Earth is divided into seven major plates and several sub plates.

Page No 265:

Question E.2.1:

Differentiate between deforestation and afforestation.

Answer:

Sl.No Deforestation Afforestation
1. A continual degradation of forests is called deforestation. Large scale planting of saplings is called afforestation.
2. Deforestation results in the complete destruction of forest resources. Afforestation helps in conserving and renewing the forest resources.

Page No 265:

Question E.2.2:

What do you understand by noise pollution? Write two common sources of noise pollution.

Answer:

The production of unwanted and unpleasant sounds, which causes disturbance to both human beings and animals is called noise pollution.
The two common sources of noise pollution are:
1. Horns of vehicles.
2. Loudspeakers being played at high volume.

Page No 265:

Question E.2.3:

What is electrical conductivity? How can liquids be affected by it?

Answer:

The measure of the ability of a material to accommodate the flow of an electric charge is called electrical conductivity.  In order for a substance to be electrically conductive, there should be freely moving charged particles in it.

In liquids, this purpose is carried out by ions. Ions are the charge carriers in liquids which are a collection of atoms with a positive or negative charge. They are formed when impurities such as salts dissolve in water which then makes it possible for the electric current to pass through, making liquids electrically conductive.

Page No 265:

Question E.2.4:

Write three main methods used to purify water at home.

Answer:

Water supplied to our homes through water mains may not be entirely free of impurities. Therefore, it is essential to purify the water at homes.The three main methods used to purify water at home are:

1. Addition of chemical tablets
2. Use of electric water filters
3. Boiling

Page No 265:

Question E.2.5:

What are the phases of moon? Write the three shapes of the moon.

Answer:

The different shapes of the moon that we see from the earth due to the revolution of moon around the earth are called phases of the moon.

The three shapes of the moon are :

  1. Crescent Moon: A very small curved portion of the moon visible to us in the shape of a crescent.
  2. Half Moon: Moon appears like a semicircle.
  3. Full Moon: Moon looks like a complete circle.

 

Page No 265:

Question F.1:

Define earthing. Why do we not get an electric shock due to earthing?

Answer:

The process of release of excess electric charges from a charged body into the earth is called earthing. Earthing allows current to flow into the earth; therefore, discharges any object. This will prevent anyone coming into contact with the charged object suffering an electric shock.

Page No 265:

Question F.2:

With the help of a labelled diagram, explain the different parts of our eye.

Answer:

The human eye is a very small sensitive organ which enables vision. The following diagram shows the internal structure of the eye. The internal parts of the eye with their functions is shown in the figure.

 

Sl.No Part of the eye Function
1. Pupil Inner aperture of the eye through which light enters
2. Iris Coloured part of the eye which regulates the amount of light entering entering the pupil by decreasing and increasing the size of the pupil
3. Sclera White part of the eye which contains clear watery fluid. It gives strength and protection to the eye.
4. Cornea A thin transparent layer in front of the eye which refracts the incoming light and also protects the rest of the eye from dust, germs and harmful foreign bodies. This is called the window of the eye.
5. Retina A lining behind the eyeball sensitive to light which has visual receptors such as rods and cones.
6. Ciliary Muscles Muscles in the eye which alter the curvature of the eye lens
7. Lens A transparent tissue between the pupil and retina which helps in focussing light
8. Optic Nerve The nerve that connects the eye to the brain transmitting impulses to the brain and back to the eye
9. Blind spot A portion in the retina insensitive to light where the nerve endings enter the optic nerve.

Page No 265:

Question F.3:

Write a short note on mercury.

Answer:

Mercury is the planet closest to the Sun and therefore not always visible due to the sun's glare. It is classified as a terrestrial or inner planet due to its proximity with the Sun. It is the smallest planet in our solar system and mostly made up of rocks. It has no atmosphere and therefore, cannot sustain life. Mercury can be seen as a bright spot in the sky during specific times of the year. In the months of  September and October, it can be seen just before sunrise and in the months of March and April it can be seen just after sunset.

Page No 265:

Question F.4:

Describe the major consequences of over-extraction of fossil fuels.

Answer:

The major consequences of over extraction of fossil fuels are:

1.Depletion of existing reserves: The over extraction of fossil fuels such as coal, gas and petroleum depletes the Earth of its existing reserves and if this continues, we will face a severe energy crisis in the near future.

2. Over-extraction of fossil fuels has environmental consequences such as:

  1. Air pollution: Burning the fuels such as coal and petroleum releases greenhouse gases into atmosphere causing  global warming. Air pollutants such as carbon monoxide, sulphur oxides and nitrogen oxides are also released  into the air causing air pollution.
  2. Threat to the biodiversity:  Coal contains toxic metals such as mercury which when released into atmosphere settle in water with the passage of time. This water enters the aquatic bodies of aquatic fauna such as fishes which in turn can harm other animals and humans who consume them.

Page No 265:

Question F.5:

What is acid rain? Give a detailed explanation on its causes and effects.

Answer:

Acid rain is an effect of air pollution. The reaction of air pollutants such as oxides of sulphur and nitrogen with water vapour and oxygen of the earth’s atmosphere results in the formation of dilute sulphuric and nitric acids. When these acids mix with rain water, they pour down as acid rain. Acid rains results in:
1. Acidification of soil which leads to the destruction of vegetation.
2. Leaching of soils and rocks.
3. Decay of building materials such as marble and lime stone.
4. Acidification of water bodies causing harm to aquatic lifeforms.



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