DPS SA 2 Class 8 Sample Papers 2017
Download Delhi Public School Class 8 SA 2 Sample papers 2017
CBSE Class 8 Sound Worksheet
1.What is noise pollution and how is it caused and write its four harmful effects
2.What is frequency , amplitude.
3.Draw waves with same frequency and different amplitude, and with same amplitude and different frequency
2.What is frequency , amplitude.
3.Draw waves with same frequency and different amplitude, and with same amplitude and different frequency
Tags:
Class 8
Class 8 Science
Sound
Worksheet
Sound CBSE Class 8 Important Question and Answers
Q.1 How does a sound making object differ from one that is silent?
Answer: Sound making object can vibrate easily.
Q.2 How does sound from a sound producing body travel through air to reach our ears?
Answer: Sound from a sound producing body travel through air to reach our ears by making regular compression and
rarefaction.
Q.3 Why are the voices of men, Women and children different?
Answer: The voices of men, women and children differ from each other due to the following factors:
(i) The pitch is one of the most essential factors to determine the voice of the individual. For example, men have lower-pitched voices while women have higher-pitched voices.
(ii) Second factor which brings in the difference in the voices is the length and the thickness of vocal cords.
Q.4 Why a sound cannot be heard on the moon?
Answer: A sound cannot be heard on the moon due to absence of medium air
Q.5 How do astronauts talk to one another on the surface of moon and Why?
Answer: Astronauts communicate with the help of radio waves on moon because these waves do not need a medium to travel
Q.6 If you want to hear a train approaching from far away, why is it more convenient to put the ear to the track?
Answer: This is because sound can travel through railway track (solid ) faster than through air.
Q.7 State one observation from everyday life which shows that sound travels much more slowly than light?Answer: We hear thunder after lightining.
Q.8 What is the scientific name for the following? The number of vibrations made per second.
Answer: Frequency
Q.9 Why do we not hear the screams of a bat?
Answer: This is because the screams are ultra sonic(above 20,000 hertz) which human ear cannot hear.
Q.10 Which of the following frequency of sound can be heard by a dog but not by a man? (a) 50,000 hertz (b) 15,000 hertz
Answer: A sound of frequency 50,000 hertz can be heard by a dog but not by a man
Q.11 Explain how, noise pollution {or excessive loud noise} is harmful to human beings.
Answer: Noise pollution can lead to a number of health-related problems. Some of them are as follows:
(i) Hearing loss (ii) inability to sleep (iii) Hypertension (iv) Severe headache (v) Stress
Q.12 State the various measures which can be taken to control {or reduce} noise pollution in our surroundings.
Answer: Noise pollution can be reduced by using silencers in vehicles, industrial machines, and home appliances reducing use of vehicle horns, running TV, radio and music systems at low volumes. Planting of trees along roads and buildings also help to reduce noise pollution.
Q.13 Give two causes of noise pollution from the homes.
Answer: . In the home noise pollution is caused by television radio and music systems at high volume, some kitchen appliances, desert coolers, air conditioners etc.
Q.14 Sound of different pitch can be produced using a flute. Explain, how?
Answer: If we blow a flute, the air column vibrates and produces sound. Flute contains small air columns, when air is bowed through the mouth piece the air columns start vibrating which produces sound.
Q.15.How does Sound produced by humans?
Answer: In humans sound is produced by the vioce box or larynx. It is the upper part of the wind pipe. Two vocal cords are stretched across the voice box leaving a narrow slit. When the lungs force air through the slit, it vibrates and produces sound.
Q. 16. How Jal Tarang produces sound?
Answer: In Jal-tarang musical instrument the cup containing minimum water produces the sound of lowest frequency or lowest pitch. As the amount of water in the cup goes on increasing, the frequency (or the pitch) of the sound produced also goes on increasing.
Q. 17. If 125 oscillations are produced in 5 seconds, what is the frequency in hertz?
Answer: in 5 seconds 125 oscillations are produced
So, in 51 seconds 125/5 = 25 oscillations are produced Hence, the frequency = 25Hz
Q. 18. What is the frequency of a vibrating body whose time-period is 0.05 second?
Answer: f = 1/t = 1/0.05 = 100/5 = 20HZ
Q. 18. State true or false
(i) Sound can be produced by beating an object irrespective of whether there are vibrations or not.
(ii)The sound of a tabla normally has a lower pitch than the sound of a violin.
(ii)A short flute will produce sound of lower pitch than a long flute.
Answer:
(i) –False [Sound is produced from a vibrating object.]
(ii) -True [The sound of a tabla normally has a lower pitch than the sound of a violin.]
(iii) –True[A short flute will produce sound of lower pitch than a long flute.]
Q.19. Give reasons Why Trees planted along the roads reduce noise?
Answer: Trees are planted along the roads and around buildings so that it could cut off sound vibrations produced from vehicles speakers etc. by absorbing them, hence leading in prevention of Noise pollution.
Q.20. what are transverse and longitudinal waves?
Answer: Longitudinal waves: A wave in which the particles of the medium vibrate back and forth in the same direction in which the wave is moving is called longitudinal wave. Example: sound waves.
Transverse waves: A wave in which the particles of the medium vibrate at right angles to the direction, in which the wave is moving, is called transverse wave. Example: Light waves.
Q.21. Explain how bats use ultrasounds to catch a prey ?
Ans: Bats search out prey and fly in dark night by emitting and detecting reflections of ultrasonic waves. The high pitched ultrasonic squeaks of the bat are reflected from the obstacles or prey and returned to bat’s ear. The nature of reflection tells the bat where the obstacle or prey is and what it is like.
Q.22. Explain how moths of certain families are able to escape capture from a bat ?
Ans: Moths of certain families have very sensitive hearing equipment. These moths can hear the high frequency squeaks of the bat and know where a bat is flying nearby and are able to escape capture.
Q. 23.How does the ear drum of human ear vibrate ?
When a compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly the eardrum moves outward when a rarefaction reaches it. In this way the eardrum vibrates.
Q. What is the role of hammer bone, anvil bone, stirrup bone and cochlea of human ear in hearing a sound
Ans: The vibrations due to the ear drum is amplified several times by three bones in the middle ear. The pressure variations in the inner ear turned in to electrical signals by the cochlea.
Q.24. How does the stethoscope help the doctors in listening to the sound of the patients heart beat?
Ans. In a stethoscope, the sound produced within the body of a patient is picked up by a sensitive diaphragm and then reaches the doctor's ear by multiple reflections. Q.3. Explain how defects in a metal block can be detected using ultrasound. Ans. To detect minor cracks or flaws in metal block, ultrasonic waves are allowed to pass through metal blocks and detectors are used to detect the transmitted waves. If there is a crack in metal block, these waves get reflected back
Q.25. How is ultrasound used for cleaning?
Ans. The object to be cleaned is put in a tank fitted with ultrasonic vibrator. The tank is filled with cleaning solution. As the ultrasonic vibrator is switched on, high frequency vibrations are set up and the dust, grease and dust particles get detached and the object gets thoroughly cleaned
26.What is the difference between noise and music? Can
music become noise
sometimes? Answer: Sound making object can vibrate easily.
Q.2 How does sound from a sound producing body travel through air to reach our ears?
Answer: Sound from a sound producing body travel through air to reach our ears by making regular compression and
rarefaction.
Q.3 Why are the voices of men, Women and children different?
Answer: The voices of men, women and children differ from each other due to the following factors:
(i) The pitch is one of the most essential factors to determine the voice of the individual. For example, men have lower-pitched voices while women have higher-pitched voices.
(ii) Second factor which brings in the difference in the voices is the length and the thickness of vocal cords.
Q.4 Why a sound cannot be heard on the moon?
Answer: A sound cannot be heard on the moon due to absence of medium air
Q.5 How do astronauts talk to one another on the surface of moon and Why?
Answer: Astronauts communicate with the help of radio waves on moon because these waves do not need a medium to travel
Q.6 If you want to hear a train approaching from far away, why is it more convenient to put the ear to the track?
Answer: This is because sound can travel through railway track (solid ) faster than through air.
Q.7 State one observation from everyday life which shows that sound travels much more slowly than light?Answer: We hear thunder after lightining.
Q.8 What is the scientific name for the following? The number of vibrations made per second.
Answer: Frequency
Q.9 Why do we not hear the screams of a bat?
Answer: This is because the screams are ultra sonic(above 20,000 hertz) which human ear cannot hear.
Q.10 Which of the following frequency of sound can be heard by a dog but not by a man? (a) 50,000 hertz (b) 15,000 hertz
Answer: A sound of frequency 50,000 hertz can be heard by a dog but not by a man
Q.11 Explain how, noise pollution {or excessive loud noise} is harmful to human beings.
Answer: Noise pollution can lead to a number of health-related problems. Some of them are as follows:
(i) Hearing loss (ii) inability to sleep (iii) Hypertension (iv) Severe headache (v) Stress
Q.12 State the various measures which can be taken to control {or reduce} noise pollution in our surroundings.
Answer: Noise pollution can be reduced by using silencers in vehicles, industrial machines, and home appliances reducing use of vehicle horns, running TV, radio and music systems at low volumes. Planting of trees along roads and buildings also help to reduce noise pollution.
Q.13 Give two causes of noise pollution from the homes.
Answer: . In the home noise pollution is caused by television radio and music systems at high volume, some kitchen appliances, desert coolers, air conditioners etc.
Q.14 Sound of different pitch can be produced using a flute. Explain, how?
Answer: If we blow a flute, the air column vibrates and produces sound. Flute contains small air columns, when air is bowed through the mouth piece the air columns start vibrating which produces sound.
Q.15.How does Sound produced by humans?
Answer: In humans sound is produced by the vioce box or larynx. It is the upper part of the wind pipe. Two vocal cords are stretched across the voice box leaving a narrow slit. When the lungs force air through the slit, it vibrates and produces sound.
Q. 16. How Jal Tarang produces sound?
Answer: In Jal-tarang musical instrument the cup containing minimum water produces the sound of lowest frequency or lowest pitch. As the amount of water in the cup goes on increasing, the frequency (or the pitch) of the sound produced also goes on increasing.
Q. 17. If 125 oscillations are produced in 5 seconds, what is the frequency in hertz?
Answer: in 5 seconds 125 oscillations are produced
So, in 51 seconds 125/5 = 25 oscillations are produced Hence, the frequency = 25Hz
Q. 18. What is the frequency of a vibrating body whose time-period is 0.05 second?
Answer: f = 1/t = 1/0.05 = 100/5 = 20HZ
Q. 18. State true or false
(i) Sound can be produced by beating an object irrespective of whether there are vibrations or not.
(ii)The sound of a tabla normally has a lower pitch than the sound of a violin.
(ii)A short flute will produce sound of lower pitch than a long flute.
Answer:
(i) –False [Sound is produced from a vibrating object.]
(ii) -True [The sound of a tabla normally has a lower pitch than the sound of a violin.]
(iii) –True[A short flute will produce sound of lower pitch than a long flute.]
Q.19. Give reasons Why Trees planted along the roads reduce noise?
Answer: Trees are planted along the roads and around buildings so that it could cut off sound vibrations produced from vehicles speakers etc. by absorbing them, hence leading in prevention of Noise pollution.
Q.20. what are transverse and longitudinal waves?
Answer: Longitudinal waves: A wave in which the particles of the medium vibrate back and forth in the same direction in which the wave is moving is called longitudinal wave. Example: sound waves.
Transverse waves: A wave in which the particles of the medium vibrate at right angles to the direction, in which the wave is moving, is called transverse wave. Example: Light waves.
Q.21. Explain how bats use ultrasounds to catch a prey ?
Ans: Bats search out prey and fly in dark night by emitting and detecting reflections of ultrasonic waves. The high pitched ultrasonic squeaks of the bat are reflected from the obstacles or prey and returned to bat’s ear. The nature of reflection tells the bat where the obstacle or prey is and what it is like.
Q.22. Explain how moths of certain families are able to escape capture from a bat ?
Ans: Moths of certain families have very sensitive hearing equipment. These moths can hear the high frequency squeaks of the bat and know where a bat is flying nearby and are able to escape capture.
Q. 23.How does the ear drum of human ear vibrate ?
When a compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly the eardrum moves outward when a rarefaction reaches it. In this way the eardrum vibrates.
Q. What is the role of hammer bone, anvil bone, stirrup bone and cochlea of human ear in hearing a sound
Ans: The vibrations due to the ear drum is amplified several times by three bones in the middle ear. The pressure variations in the inner ear turned in to electrical signals by the cochlea.
Q.24. How does the stethoscope help the doctors in listening to the sound of the patients heart beat?
Ans. In a stethoscope, the sound produced within the body of a patient is picked up by a sensitive diaphragm and then reaches the doctor's ear by multiple reflections. Q.3. Explain how defects in a metal block can be detected using ultrasound. Ans. To detect minor cracks or flaws in metal block, ultrasonic waves are allowed to pass through metal blocks and detectors are used to detect the transmitted waves. If there is a crack in metal block, these waves get reflected back
Q.25. How is ultrasound used for cleaning?
Ans. The object to be cleaned is put in a tank fitted with ultrasonic vibrator. The tank is filled with cleaning solution. As the ultrasonic vibrator is switched on, high frequency vibrations are set up and the dust, grease and dust particles get detached and the object gets thoroughly cleaned
Ans.The unpleasant sound is called noise. Whereas pl easant sound is called music. Noise can produce so many health hazards, whereas noise m usic brings about soothing effect. Yes, music can become a noise sometimes when the mu sical instruments produce very high volume sounds.
27.On what factors pitch and loudness of the sound depends
Ans.The pitch of the sound depends on frequency,
and the loudness of the sound depends on the amplitude.
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Class 8
STARS AND THE SOLAR SYSTEM CBSE Class 8 Important Question Solutions
Short Answers
Q.1.Name the planet
appears I the northern sky before sun rise?
Ans: Venus brightest
of all planets
|
Q.2. Name the planet
which has 28 moons?
|
Ans: Jupiter manly
consist of hydrogen and helium gases
|
Q.3. In which direction
stars move except Polar star? |
Tags:
Class 8
Class 8 Mensuration Important Questions Worksheet
1.In a building there are 4 cylindrical pillars. T
he radius of each pillar is 21 cm and
height is 5 m. Find the curved surface area of four
pillars.
Reaching The Age of Adolescene Important Question and Answers
SCIENCE REACHING THE AGE OF ADOLESCENCE
Important Question and Answers
Q. What do you mean by adolescence?
Answer: The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence. Adolescence begins around the age of 11 and lasts up to 18 or 19 years of age. In girls, adolescence may begin a year or two earlier than in boys
Important Question and Answers
Q. What do you mean by adolescence?
Answer: The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence. Adolescence begins around the age of 11 and lasts up to 18 or 19 years of age. In girls, adolescence may begin a year or two earlier than in boys
Reaching the Age of Adolescence CBSE Class 8 Important Notes
What is Adolescence or Adolescent Age?
The period of life, when the body undergoes changes, leading to reproductive maturity is called
adolescence. It begins around the age of 11 years and lasts up to 18 or 19 years of age. Adolescents are
also called ‘teenagers’, In girls, adolescence begins a year or two earlier than in boys.
During adolescence, the human body undergoes a number of changed. The testes start to make sperms
and the ovaries start to make eggs. In other words, the reproductive organs become functional. The age
at which reproductive organs become functionally active is called puberty. At puberty, therefore the
boys and girls become capable of reproduction.
The period of life, when the body undergoes changes, leading to reproductive maturity is called
adolescence. It begins around the age of 11 years and lasts up to 18 or 19 years of age. Adolescents are
also called ‘teenagers’, In girls, adolescence begins a year or two earlier than in boys.
During adolescence, the human body undergoes a number of changed. The testes start to make sperms
and the ovaries start to make eggs. In other words, the reproductive organs become functional. The age
at which reproductive organs become functionally active is called puberty. At puberty, therefore the
boys and girls become capable of reproduction.
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Cbse Science notes
Class 8
Coal and Petroleum CBSE Class 8 Important Question and Answers
State whether the following statements are true or false :-
a. The percentage of carbon is more in coke than in coal.
b. Petroleum is soluble in water.
c. Petroleum is an exhaustible or non renewable energy source.
d. Ammoniacal liquor is formed by solution of ammonia in oil.
e. Natural gas is a domestic and industrial fuel with high calorific value.
Ans.true, false, true, false, true .
2.What are petrochemicals? Explain.
Ans.Many useful products are obtained from petroleum and natural gas. They are called
petrochemicals.
These petrochemicals are the raw materials for the manufacture of the synthetic fibres
(nylon, acrylic, polyester etc) and detergents and many other useful polymers. Natural
gas yields which is used in the manufacture of ammonia which is further employed as
a raw material in the manufacture of fertilisers like urea.
a. The percentage of carbon is more in coke than in coal.
b. Petroleum is soluble in water.
c. Petroleum is an exhaustible or non renewable energy source.
d. Ammoniacal liquor is formed by solution of ammonia in oil.
e. Natural gas is a domestic and industrial fuel with high calorific value.
Ans.true, false, true, false, true .
2.What are petrochemicals? Explain.
Ans.Many useful products are obtained from petroleum and natural gas. They are called
petrochemicals.
These petrochemicals are the raw materials for the manufacture of the synthetic fibres
(nylon, acrylic, polyester etc) and detergents and many other useful polymers. Natural
gas yields which is used in the manufacture of ammonia which is further employed as
a raw material in the manufacture of fertilisers like urea.
Chemical Effects of Electric Current CBSE Class 8 Important Questions
Class–VIII Science (Chemical Effects of Electric Current
Q.1Fill in the blanks
a. Electrolysis is used for ______ one metal over another metal.
b. A combination of cells is known as ______ .
c. In liquid the moving charges are called ______ .
d. The driving force that carries charges around a circuit is ______ force.
e. Electric current is the flow of negatively charged particles called ______
Ans.electroplating, battery, ions, electromotive, electrons.
Q2.Fill in the blanks :-
a. An electric current can bring about a ______ change.
b. An ______ when dissolved in water, breaks up into ions.
c. ______ are materials that allow electricity to flow through them.
d. ______ are also called as insulators.
e. A source of electricity is called a ______ .
Ans.chemical, electrolyte, conductors, non- conductors, cell.
Q2. What is the actual direction of electric current?
Ans.Electrons flow from an electron rich body/object to an electron deficit one. In other
words from a body that is negatively charged to a body that is positively charged.
However, scientists from earlier days thought that electric current is the flow of
positive charge from a positively charged body to a negatively charged body.
Therefore, they took this as the direction of flow of current.
Today, we consider the flow of conventional electric current to be from positive to
negative electrode
3. Why is it dangerous to handle electrical appliances with wet hands or while standing
on a wet floor ?
Ans.Small amounts of mineral salts are present naturally in water. They are beneficial for
human health. However, these salts make water conducting as such if we touch an
electrical appliance with wet hands or while standing on a wet floor, current will flow
through our body and result will be an electric shock.
4.Define electrolysis. Through diagram represent movement of ions during electrolysis.
Ans.If any substance conducts electricity when dissolved in water and breaks up into its
constituents during the process of dissolving, is known as an electrolyte. The process
of breaking down of an electrolyte on passing electric current through it is called
electrolysis.
5. Write one important application of electrolysis in our daily life.
Ans.Electrolysis has many applications in our daily life but the most common of all the
applications is electroplating. In the process of electroplating, a thin layer of a metal
like gold, silver, chromium, tin, nickel etc is coated over another cheaper metal either
to protect the cheaper metal or to make that metal look attractive
6. Pick the odd word out of the following:
salt solution, sugar solution, lime water, tap water, river water.
Ans.Except sugar all solution will conduct electricity
7. Is electric shock lethal? What should be done in case of electric shock?
Ans.The electric shocks vary in their effect, as they can be mild to severe, sometimes they
even lead to death i.e. lethal.
Electric shocks can cause severe burns and tissue damage. The function of the heart
can also be disrupted by a strong electric shock. Irreparable injury to vital organs
result into lethality. If shock occurs indoors, immediate disconnection of power supply
is required. If a person is in contact with source of electric current, stand on a dry
rubber mat, wooden slab etc and try to move the person using a completely dry
wooden pole.
8. What is deplating? How is it useful?
Ans.The process just opposite to electroplating is deplating. In this process, the object to
be deplated is used as the anode ( positively charged electrode) and the recovered
metal is deposited on a cathode (negatively charged electrode) usually of the same
metal.
To recover gold and other valuable metals from the circuits of computers, mobiles,
other electronic goods, the process of deplating is very useful.
9.Describe the specific features of an LED?
Ans.An LED or light emitting diode is an electronic device. It lights up (starts emitting
light) even when a very weak current flows through it. It contains two leads (as shown
in worksheet 68) one of which is longer than the other. The longer lead is connected to
the cell/battery. Hence when current flowing through the circuit is too weak then bulb
may not glow at all so for such cases we can utilise LED which is a more sensitive
detector of current.
10. Chrome plating is very popular in the industry. What are its pros and cons?
Ans.Chrome plated objects have a good lustrous shine and appear attractive. They are
scratch and corrosion resistant. Therefore, chromium plating is done on large number
of objects, like fancy lights, bathroom accessories, kitchen appliances, automobile
parts etc.
However, chrome plating is done in a bath (solution) of chromic acid, which is
considered carcinogenic and has been known to be poisonous/toxic and cause sores
and ulcers etc.
11.Are conductors and electrolytes same? If not explain differences between them with
examples.
Ans.Materials that allow electricity to flow through them are called conductors.
Conductors like, silver, gold, copper, mercury, aluminium, iron, graphite etc are
elements, and remain unchanged when they conduct electricity.
Substances which conduct electricity when dissolved in water or when melted are
called electrolytes. In solution or in molten state, electrolyte decomposes into ions that
are charged particles and conduct electricity. Example: common salt, vinegar, caustic
soda etc.
12. Purification of metals is possible through electrolysis. Describe this application.
Ans.Purification of metals can be done by electrorefining, where metals are refined by
electrolytic method. For example: copper, silver, nickel, gold, aluminium etc purified
through electrorefipning.
The purified metal after electrolysis deposits at the negatively charged electrode i.e.
the cathode and is collected from time to time.
Q13.State whether the following statements are true or false :-
a. Natural water that runs down the hills is 100% pure water.
b. Formation of a new chemical compound by electricity is electrolysis.
c. Kerosene is a non electrolyte.
d. Lemon juice is an electrolyte.
e. All liquids conduct electricity.
Ans.false, false, true, true, false.
Q14.State whether the following statements are true or false :-
a. Passing electric currents through a conducting liquid causes chemical changes.
b. Electrolysis is an application of electroplating.
c. Vinegar is a conductor of electricity.
d. A solution that contains oppositely charged ions conducts electricity.
e. Glucose solution is an electrolyte and hence conducts electricity.
Ans.true, false, true, true, false.
Q15.State whether the following statements are true or false :-
a. Every ion has both positive as well as negative charges.
b. Electricity is a form of energy.
c. Asbestos is a good conductor of electricity.
d. Current flows in a closed circuit as well as an open circuit.
e. Different LEDs may give out light of different colours.
Ans.false, true, false, false, true.
Q.1Fill in the blanks
a. Electrolysis is used for ______ one metal over another metal.
b. A combination of cells is known as ______ .
c. In liquid the moving charges are called ______ .
d. The driving force that carries charges around a circuit is ______ force.
e. Electric current is the flow of negatively charged particles called ______
Ans.electroplating, battery, ions, electromotive, electrons.
Q2.Fill in the blanks :-
a. An electric current can bring about a ______ change.
b. An ______ when dissolved in water, breaks up into ions.
c. ______ are materials that allow electricity to flow through them.
d. ______ are also called as insulators.
e. A source of electricity is called a ______ .
Ans.chemical, electrolyte, conductors, non- conductors, cell.
Q2. What is the actual direction of electric current?
Ans.Electrons flow from an electron rich body/object to an electron deficit one. In other
words from a body that is negatively charged to a body that is positively charged.
However, scientists from earlier days thought that electric current is the flow of
positive charge from a positively charged body to a negatively charged body.
Therefore, they took this as the direction of flow of current.
Today, we consider the flow of conventional electric current to be from positive to
negative electrode
3. Why is it dangerous to handle electrical appliances with wet hands or while standing
on a wet floor ?
Ans.Small amounts of mineral salts are present naturally in water. They are beneficial for
human health. However, these salts make water conducting as such if we touch an
electrical appliance with wet hands or while standing on a wet floor, current will flow
through our body and result will be an electric shock.
4.Define electrolysis. Through diagram represent movement of ions during electrolysis.
Ans.If any substance conducts electricity when dissolved in water and breaks up into its
constituents during the process of dissolving, is known as an electrolyte. The process
of breaking down of an electrolyte on passing electric current through it is called
electrolysis.
5. Write one important application of electrolysis in our daily life.
Ans.Electrolysis has many applications in our daily life but the most common of all the
applications is electroplating. In the process of electroplating, a thin layer of a metal
like gold, silver, chromium, tin, nickel etc is coated over another cheaper metal either
to protect the cheaper metal or to make that metal look attractive
6. Pick the odd word out of the following:
salt solution, sugar solution, lime water, tap water, river water.
Ans.Except sugar all solution will conduct electricity
7. Is electric shock lethal? What should be done in case of electric shock?
Ans.The electric shocks vary in their effect, as they can be mild to severe, sometimes they
even lead to death i.e. lethal.
Electric shocks can cause severe burns and tissue damage. The function of the heart
can also be disrupted by a strong electric shock. Irreparable injury to vital organs
result into lethality. If shock occurs indoors, immediate disconnection of power supply
is required. If a person is in contact with source of electric current, stand on a dry
rubber mat, wooden slab etc and try to move the person using a completely dry
wooden pole.
8. What is deplating? How is it useful?
Ans.The process just opposite to electroplating is deplating. In this process, the object to
be deplated is used as the anode ( positively charged electrode) and the recovered
metal is deposited on a cathode (negatively charged electrode) usually of the same
metal.
To recover gold and other valuable metals from the circuits of computers, mobiles,
other electronic goods, the process of deplating is very useful.
9.Describe the specific features of an LED?
Ans.An LED or light emitting diode is an electronic device. It lights up (starts emitting
light) even when a very weak current flows through it. It contains two leads (as shown
in worksheet 68) one of which is longer than the other. The longer lead is connected to
the cell/battery. Hence when current flowing through the circuit is too weak then bulb
may not glow at all so for such cases we can utilise LED which is a more sensitive
detector of current.
10. Chrome plating is very popular in the industry. What are its pros and cons?
Ans.Chrome plated objects have a good lustrous shine and appear attractive. They are
scratch and corrosion resistant. Therefore, chromium plating is done on large number
of objects, like fancy lights, bathroom accessories, kitchen appliances, automobile
parts etc.
However, chrome plating is done in a bath (solution) of chromic acid, which is
considered carcinogenic and has been known to be poisonous/toxic and cause sores
and ulcers etc.
11.Are conductors and electrolytes same? If not explain differences between them with
examples.
Ans.Materials that allow electricity to flow through them are called conductors.
Conductors like, silver, gold, copper, mercury, aluminium, iron, graphite etc are
elements, and remain unchanged when they conduct electricity.
Substances which conduct electricity when dissolved in water or when melted are
called electrolytes. In solution or in molten state, electrolyte decomposes into ions that
are charged particles and conduct electricity. Example: common salt, vinegar, caustic
soda etc.
12. Purification of metals is possible through electrolysis. Describe this application.
Ans.Purification of metals can be done by electrorefining, where metals are refined by
electrolytic method. For example: copper, silver, nickel, gold, aluminium etc purified
through electrorefipning.
The purified metal after electrolysis deposits at the negatively charged electrode i.e.
the cathode and is collected from time to time.
Q13.State whether the following statements are true or false :-
a. Natural water that runs down the hills is 100% pure water.
b. Formation of a new chemical compound by electricity is electrolysis.
c. Kerosene is a non electrolyte.
d. Lemon juice is an electrolyte.
e. All liquids conduct electricity.
Ans.false, false, true, true, false.
Q14.State whether the following statements are true or false :-
a. Passing electric currents through a conducting liquid causes chemical changes.
b. Electrolysis is an application of electroplating.
c. Vinegar is a conductor of electricity.
d. A solution that contains oppositely charged ions conducts electricity.
e. Glucose solution is an electrolyte and hence conducts electricity.
Ans.true, false, true, true, false.
Q15.State whether the following statements are true or false :-
a. Every ion has both positive as well as negative charges.
b. Electricity is a form of energy.
c. Asbestos is a good conductor of electricity.
d. Current flows in a closed circuit as well as an open circuit.
e. Different LEDs may give out light of different colours.
Ans.false, true, false, false, true.
Delhi Public School Science Sample Paper S.A 1 Class 8
DELHI PUBLIC SCHOOL, CHANDIGARH
Summative Assessment-I, Session 2014-15
Class : VIII, Subject : Science (Sample Paper)
Time : 3 hours MM : 90
Section-A (Physics)
Q1 Choose and write the correct option: (1 x 4 = 4)
(i) An image is formed in
(a) regular reflection (b) diffused reflection
(c) irregular reflection (d) none
Ans.Regular Reflection
(ii) When two plane mirrors are held at an angle of 60°, the number of images formed are
(a) 5 (b) 6
(c) 3 (d) 4
Ans.5
Summative Assessment-I, Session 2014-15
Class : VIII, Subject : Science (Sample Paper)
Time : 3 hours MM : 90
Section-A (Physics)
Q1 Choose and write the correct option: (1 x 4 = 4)
(i) An image is formed in
(a) regular reflection (b) diffused reflection
(c) irregular reflection (d) none
Ans.Regular Reflection
(ii) When two plane mirrors are held at an angle of 60°, the number of images formed are
(a) 5 (b) 6
(c) 3 (d) 4
Ans.5
Tags:
Class 8
Sample paper
Science
Microorganisms Friends and Foe Class 8 CBSE Ncert Solutions
1.
Fill in the blanks
.
a. Microorganisms can be seen with the help of a microscope .
b. Blue green algae fix nitrogen directly from air to enhance fertility of soil.
c. Alcohol is produced with the help of yeast .
d. Cholera is caused by bacteria
a. Microorganisms can be seen with the help of a microscope .
b. Blue green algae fix nitrogen directly from air to enhance fertility of soil.
c. Alcohol is produced with the help of yeast .
d. Cholera is caused by bacteria
CELL - STRUCTURE AND FUNCTIONS Class 8 CBSE NCERT Solutions
NCERT Book Solutions of Cell Structure and Functions
1. Indicate whether the following statements are True or False.
a. Unicellular organisms have one celled body. True
b. Muscle cells are branched. False
c. The basic living unit of an organism is an organ. False
d. Amoeba has irregular shape. True
1. Indicate whether the following statements are True or False.
a. Unicellular organisms have one celled body. True
b. Muscle cells are branched. False
c. The basic living unit of an organism is an organ. False
d. Amoeba has irregular shape. True
Metals and Non Metals Important Question and Answers
One Word Answers
1.Which metal is liquid at room temperature other than mercury?Ans.Gallium
2.Which non metal is lustrous and shiny?
Ans.Iodine
Metals and Non Metals Notes Class 8 CBSE
Metals
They are elements which lose electrons to form cations and are electropositive, e.g Iron,Zinc,Calcium etc.
They are elements which lose electrons to form cations and are electropositive, e.g Iron,Zinc,Calcium etc.
Class 8 Science Synthetic Fibres and Plastics Important MCQs
Here are some important multiple choice question for you to revise from Synthetic Fibres and plastics
Class 8 Science Plastics Notes and Important Points
Plastics
Any Synthetic material which can be easily moulded into any desired shape on heating is called plastic.Plastic is also a polymer like the synthetic fibres.There are two types of arrangement in plastics linear and cross linked.
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