On this Page we have given West Bengal Class 8 English Medium Science Solution Chapter 1 (Force and Pressure, Forces Active Without Contact, Heat, Light) Question and Answer for our Students of West bengal Class 8 English Medium. Hope this following Question Answer will help our Students.
West Bengal Class 8 | Chapter 1 | Force and Pressure, Forces Active Without Contact, Heat, Light
(1) MCQ
(1) Which of the following is correct measurement of pressure ?
(a) Force × Area
(b) Force/Area
(c) Mass × acceleration
(d) Mass/acceleration
Ans –(b)
(2) Newton is the unit of _____
(a) Force
(b) Pressure
(c) Density
(d) Atmospheric pressure
Ans – (a)
(3) 1Kg = ______ N
(a) 9.1
(b) 9.7
(c) 9.8
(d) 9.0
Ans –(c)
(4) Which of the following force defines gravity ?
(a) Repulsive force
(b) Attractive force
(c) Attractive and repulsive force
(d) None of the above
Ans – (b)
(5) Which of the following is an example of non-contact force ?
(a) Force exerted by magnet
(b) Force exerted by car on road
(c) Force exerted by a man to lift a weight
(d)None of the above
Ans – (a)
(6) The terms Force and motion stated by _____
(a) Sir Isaac Newton
(b) Robert Einstein
(c) Neil Bohr
(d) Mendeleev
Ans – (a)
(7) If the force is doubled , then the acceleration should be ____
(a) Tripled
(b) Changes some magnitude
(c) Remains same
(d) Doubled
Ans – (d)
(8) The force exerted by Earth on the object and it’s the object towards itself is called ___
(a) Contact force
(b) Gravitational force
(c) Muscular force
(d) Magnetic force
Ans – (b)
(9) The force between two surfaces opposes the motion of each other called as _____
(a) Gravitational force
(b) Magnetic force
(c) Frictional force
(d) Non-contact force
Ans – (c)
(10) Mass of unit volume of any substance is known as ____
(a) Force
(b) Density
(c) Pressure
(d) Newton
Ans – (b)
(11) When object is inserted in liquid, the liquid exerts upward force on that object is called as___
(a) Pressure
(b) Density of the object
(c) Buoyancy of the object
(d) None of the above
Ans – (c)
(12) he force exerted by any charged body on another body is called __
(a) Non-contact force
(b) Contact force
(c) Electrostatic force
(d) Gravitational force
Ans – (c)
(13) The force exerted by our muscles to lift the weight is ____
(a) Non-contact force
(b) Muscular force
(c) Contact force
(d) Gravitational force
Ans –(b)
(14) Which of the following term is measured by using spring balance.
(a) Force
(b) Pressure
(c) Mass
(d) Weight
Ans – (d)
(15) Ramesh and Akash are playing Tug of war in two teams. If the rope moves towards Akash. then which of the following statement is correct?
(a) Magnitude of force applied by team Ramesh is greater than that of team Akash
(b) Magnitude of force is same on both sides
(c ) Magnitude of force applied by Ramesh is slightly greater thanthat of Akash.
(d) Magnitude of force applied by team Ramesh is smaller than that of team Akash.
Ans – (a)
(16) When two forces act in opposite direction then the total force is termd as ___
(a) Addition of the two forces
(b) Difference between the two forces
(c) Only first force
(d) Only second force
Ans – (b)
(17) An apple falls on the ground due to
(a) Muscular force
(b) Magnetic force
(c) Static force
(d) Gravitational force
Ans – (d)
(18) Which of the following describes state of motion
(a) Position of motion
(b) Position of rest
(c) Position of static force
(d) Position of both by the set of rest or motion
Ans – (d)
(19) Sunita experiences her hairs are flying apart while combing hair , the force responsible for this is
(a) Electrostatic force
(b) Force of friction
(c) Magnetic force
(d) Gravitational force
Ans – (a)
(20) When two objects retailing each other than this repulsion is due to
(a) Magnetic force
(b) Electrostatic force
(c) Both magnetic and electrostatic force
(d) None of the above
Ans – (c)
(21) Which of the following is a contact force?
(a) Gravitational force
(b) Magnetic force
(c) Frictional force
(d) Electrostatic force
Ans – (c)
(22) Sunita throws a ball on a slope of a road, the ball rolling on the road and finally stops. Which of the following is the reason for this.
(a) Friction
(b) Sunita applied more force
(c) Sunita applied less force
(d) Due to slope of the road
Ans – (a)
(23) The direction of force of friction when it acts on moving objects is alwas ___
(a)Opposite direction
(b) Perpendicular to the direction of motion
(c) Along with the direction of motion
(d) On any direction
Ans – (b)
(24) In a tug of war, two teams pulling a rope and the rope does not move towards any of the team then which of the following statement is correct.
(a) Equal force applied in opposite direction
(b) Equal force applied in any direction
(c) No force is applied in any direction
(d) None of the above
Ans – (a)
(25) Which of the following is an example of non-contact force.
(a) Ramesh hits a football.
(b) Sushma hits a tennis ball
(c) Force of attraction between magnets
(d) Raju Pushing his car
Ans – (c)
- More Extra Questions
1.) We apply a force to a stationary object
a) To change its direction
b) To accelerate it
c) To decelerate it
d) To mobilize it
Answer: To mobilize it
2.) According to Newton’s First Law of Motion, what can be inferred if an object is stationary or its velocity remains unchanged
a) No force is operating on the object
b) The object has a constant force acting on it
c) The object is undergoing constant acceleration
d) The object is in a state of equilibrium
Answer: No force is operating on the object or the aggregate of forces operating on the object is zero.
3.) According to Newton’s Second Law of Motion, what happens to the acceleration of an object when the force applied to it is doubled
A) The acceleration is halved
b) The acceleration remains the same
c) The acceleration is doubled
d) The acceleration is quadrupled
Answer: The acceleration is doubled
4.) What is the relationship between the force exerted by an object and the force exerted on it, according to Newton’s Third Law of Motion
A) They are equal in magnitude and opposite in direction
b) They are directly proportional to each other
c) They are inversely proportional to each other
d) They have no relationship
Answer: They are equal in magnitude and opposite in direction
5.) A force on a particular object can be measured
a) By observing its velocity
b) By observing its acceleration
c) By observing its displacement
d) By observing its mass
Answer: By observing its acceleration
6.) The SI unit to measure force is
a) Kilogram
b) Meter
c) Newton
d) Second
Answer: Newton
7.) What will be the force applied on your hand when you are holding a weight of 1kg
A) 1 Newton
b) 9.8 Newton
c) 10 Newton
d) 100 Newton
Answer: 9.8 Newton
8.) How can you measure the force when an object is stationary and there is no acceleration
A) By observing its velocity
b) By observing its mass
c) By observing the gravitational pull
d) By observing the magnitude of acceleration
Answer: By observing the gravitational pull
9.) As per Newton’s third law of motion, what happens when a force is applied to an object
A) The object accelerates
b) The object remains stationary
c) An equal and opposite force is generated
d) The force doubles in magnitude
Answer: An equal and opposite force is generated
10.) When the weight of the suspended object is doubled, what happens in the spring expansion
A) The spring contracts
b) The spring expands further
c) The spring remains unchanged
d) The expansion of the spring is halved
Answer: The spring expands further
11.) Force can be measured using a spring balance
a) By observing the velocity of the object
b) By observing the mass of the object
c) By observing the elongation of the spring
d) By observing the acceleration of the object
Answer: By observing the elongation of the spring
12.) It is the position of the index on the scale when no weight is hung from the spring
A) Zero
b) 1 kg
c) 9.8 Newton
d) 3 kg
Answer: Zero
13.) The force exerted by a mass of 2 kg or 3 kg can be measured using the spring balance
A) By observing the position of the index on the scale
b) By measuring the mass of the object
c) By calculating the acceleration of the object
d) By observing the elongation of the spring
Answer: By observing the position of the index on the scale
14.) The index of the spring balance records 3 kg , what can be said by that
A) Each force exerted on the spring balance is equal to 3 kg
b) The mass of the spring balance is 3 kg
c) The force exerted by the spring balance is 3 kg
d) The acceleration of the spring balance is 3 kg
Answer: Each force exerted on the spring balance is equal to 3 kg
15.) 1.) What can we conclude from Newton’s first law of motion if the box does not move or remains stationary
A) A force of 9.8 Newton is applied to the left side of the box
b) The net force on the box is zero
c) The box is experiencing frictional force
d) The box is in a state of equilibrium
Answer: The net force on the box is zero
16.) _______ is the force that opposes the motion of an object
A) Gravitational force
b) Magnetic force
c) Frictional force
d) Tension force
Answer: Frictional force
17.) Speculate the magnitude of the frictional force in the case where the box remains stationary on the table
A) 0 Newton
b) 9.8 Newton
c) 19.6 Newton
d) It cannot be determined
Answer: 9.8 Newton
18.) If a stationary object is pulled with increasing force, what happens to the magnitude of the static frictional force
A) It remains constant.
b) It decreases.
c) It increases proportionally.
d) It increases up to a certain level, then decreases.
Answer: It increases proportionally
19.) If an object remains stationary on a particular surface, does the maximum magnitude of static friction of the object with the surface always remain constant
A) Yes, it always remains constant.
b) No, it changes according to the pulling force.
c) It depends on the surface roughness.
d) It depends on the weight of the object.
Answer: Yes, it always remains constant.
20.) If the mass of a body is divided by its volume the physical quantity we get is known as
a ) surface area
b ) density
c ) refractive index
d ) mass volume ratio
Answer. Density
21.) _____ is the density of water in grams per cubic centimeter (g/cc)
a) 1 g/cc
b) 10 g/cc
c) 100 g/cc
d) 1000 g/cc
Answer: 1 g/cc
22.) Mercury has a very high density of
A) 1 g/cc
b) 10 g/cc
c) 13.6 g/cc
d) 100 g/cc
Answer: 13.6 g/cc
23.) When water and mustard oil are mixed in a bowl, what can be observed
a) Water floats on oil
b) Oil floats on water
c) They mix evenly
d) They separate into distinct layers
Answer: They separate into distinct layers
24.) One of the following liquid has a greater density, water or mustard oil
a) Water
b) Mustard oil
c) They have the same density
d) Cannot be determined
Answer: Mustard oil
25.) With how much force is the earth pulling the 10 kg iron block downward
A) 10 Newton
b) 98 Newton
c) 108 Newton
d) 392 Newton
Answer: 98 Newton
26.) A 10 kg iron block remain stationary inspite of the downward force exerted by the earth
A) The block is too heavy to move.
b) The table exerts an equal and opposite upward force on the block.
c) The block Is stuck to the table.
d) The earth’s force is canceled out by air resistance.
Answer: The table exerts an equal and opposite upward force on the block.
27.) What is the pressure exerted by the block on the table if the total area of contact is 0.25 sq.m
A) 0.25 Newton/sq.m
b) 98 Newton/sq.m
c) 392 Newton/sq.m
d) 1000 Newton/sq.m
Answer: c392 Newton/sq.m
27.) The force per unit area applied on the surface of an object is known as
a ) Joule
b ) atm
c ) pressure
d ) buoyancy
Answer : pressure
28.) Water spurts out forcefully from the hole in the bottle as compared to the tumbler because
A) The earth pulls the water in the bottle with greater force.
b) The bottle has a larger area of the base.
c) The height of the water column in the bottle is greater.
d) The tumbler has a smaller capacity to hold water.
Answer: The height of the water column in the bottle is greater.
29.) If the mass of water in the bottle is 1 kg, what is the pressure of water on the base of the bottle if the area of the base is A sq.m
A) 1/A Newton/sq.m
b) 9.8/A Newton/sq.m
c) 19.8/A Newton/sq.m
d) 49/A Newton/sq.m
Answer: 9.8/A Newton/sq.m
30.) The relationship between height and pressure exerted by the liquid is
a) The greater the height, the greater the pressure.
b) The smaller the height, the greater the pressure.
c) The height of the liquid surface does not affect the pressure.
D) It is not mentioned in the passage.
Answer: The greater the height, the greater the pressure
31.) Concentrated saline water exert a greater pressure compared to plain water because
A) The density of concentrated saline water is greater than that of water.
b) The height of the liquid column is greater for concentrated saline water.
c) The mass of concentrated saline water is greater than that of plain water.
d) It is not mentioned in the passage.
Answer: The density of concentrated saline water is greater than that of water.
32.) Identity the factors which determine the pressure exerted by a liquid at a given point
a) The height of the liquid column only.
b) The density of the liquid only.
c) Both the height of the liquid column and the density of the liquid.
d) It is not mentioned in the passage.
Answer: Both the height of the liquid column and the density of the liquid.
33.) The pressure exerted by a column of water having height of _____ is equal to air pressure.
a ) 10.3 m
b ) 10.4 m
c ) 10.5 m
d ) 10.6 m
Ans. 10.3 m
34.) It is the force that a liquid exerts on an object when it is immersed in the liquid
A) Gravitation force
B) Buoyancy force
C) Frictional force
D) Magnetic force
Answer: Buoyancy force
35.) How does the reading of the spring balance change when an object is partially immersed in a liquid
A) It increases
B) It decreases
C) It remains the same
D) It fluctuates
Answer: It decreases
36.) Does the magnitude of the buoyant force depend on the extent to which the object is immersed in the liquid
A) Yes, It depends on the extent of immersion
B) No, it remains the same regardless of immersion
C) It depends on the density of the object
D) It depends on the temperature of the liquid
Answer: Yes, it depends on the extent of immersion
37.) A steel bowl, which is heavier than a small nail, float on water because
A) The bowl has a larger surface area
B) The bowl is less dense than water
C) The bowl displaces more liquid than the nail
D) The bowl experiences greater buoyancy force
Answer: The bowl is less dense than water
38.) The weight of the displaced liquid is equal to the magnitude of _______ force
a ) upward
b) downward
c) sideways
d ) diagonal
Answer. Upward
39.) He was the first person to conceptualize the concept of Buoyancy
a ) Albert Aldrin
b ) Warren Buffett
c ) Archimedes
d ) Schweinfurt
Ans. Archimedes
40.) If an object floats in a liquid, the weight of the object and the weight of the displaced liquid are ____
a ) different
b ) same
c ) massively different
d ) cannot be said
Answer. Same
Q.(2) Very short answer.
(1) What is the formula of pressure ?
→ Pressure = force / area
(2) Define force and give its unit.
→ The force is defined as push or pull upon an object resulting an object’s interaction with another object.
(3) Define atmospheric pressure.
→The pressure exerted by air is called as atmospheric pressure.
(4) Write the name of the force which acts on every object.
→Gravitational force acts on every object.
(5) What is pressure ?
→The force per unit area applied to the surface of an object is called as pressure.
(6) What is frictional force ?
→ The force generated between two surfaces of contact, opposes the motion of the object , or any attempt to move the object is called as fictional force.
(7) What is static friction ?
→ When the object is stationary on the surface, even though it has been pulled by the force it is called as static friction.
(8) What happened with the opposite frictional force when the pulling force is increasing continuously ?
→The frictional force is increasing to some extent and the object will cease to be stationary and will starts to move. The opposite frictional force doesn’tincrease with increasing pulling force.
(9) What is the term density ? Give its unit.
→Mass of unit volume of any substance is called as density. The unit of density is gram per cubic centimeter.
(10) What do you mean by the term buoyancy ?
→ When an object is immersed in a liquid, then the liquid exerts upward force on that object is called as buoyancy.
(11) Define gravitational force.
→ The earth pulls all the objects in the universe towards itself with the force called as the gravitational force.
(12) What is the use of spring balance?
→Spring balance is used to measure the weight of any object with the help of Earth’s gravitational force.
(13) Give the unit of universal gravitational constant.
→ The universal gravitational constant denoted by ‘G’ . The unit of universal gravitational constant ( G ) is Nm^2 / Kg^2
(14) State the magnitude of the force exerted by Earth on an object of 1 kilogram.
→ The magnitude of force exerted by Earth on an object of 1 kilogram is 9.8 N.
(15) Define free falling object ?
→ When an object is falling freely towards Earth due to gravitation is called as free-falling object.
(16) What is induction ?
→ In presence of charged object, the opposite ends of a neutral object will develop opposite electrical charges. This phenomenon is called as an induction.
(17) Define the term unit heat ?
→ The amount of heat required for 1 gram of pure water to raise its temperature by 1 degree Celsius is called as unit heat.
(18) Define the term melting point.
→ The temperature at which solid phase converted into liquid phase and both the phase are in equilibrium is called as melting point.
(19) What do you mean by the term solidification ?
→ When the substance changes from liquid state to solid state by giving up heat then it is called as solidification.
(20) What is freezing ?
→ Freezing is also known as solidification. When the substance changes from liquid state to solid state by giving up the heat is called as freezing or solidification.
(21) What will happen with the volume when water freezes ?
→ When water freezes the volume of ice will increases.
(22) Write the two factors which affects the melting point.
→
- Nature of the substance
- Pressure
(23) Explain the term latent heat for that change of state.
→ The quantity of heat required by unit mass of substance for a particular change of state is called as latent heat for that change of state.
(24) What is evaporation ?
→ Evaporation is the process in which liquid is slowly converted into its vapor.
(25) What is boiling ?
→The process in which liquid is rapidly converted into its vapor is called as boiling.
(26) Define the term boiling point?
→ The temperature at which pure liquid starts boiling and it remains constant throughout the process called as boiling point.
(27) Write the factors affecting boiling point.
→
- Nature of the liquid
- Impurities present in the liquid
- Super incumbent pressure on the liquid.
(28) State the boiling points of following.
→
- Mercury – 357 degrees Celsius
- Water – 100 degrees Celsius
(29) Explain the term condensation ?
→ The process in which water vapors changes into liquid phase is called as condensation.
(30) What do you mean by the fog?
→ Air Gets saturated by the water vapor , and finally the water vapor present in the region condenses to a small droplet around the dust particles suspended in the air. These droplets called as fog.
Q.(3) Short answer questions.
(1) Why diamonds look shiny?
→ Refractive index of diamond with respect to air is very high. So critical angle of diamond with respect to air is very low. Diamonds are cut in such a way that light ray’s incident on inner surface of the diamond at angles greater than critical angle suffers total internal reflection. After such reflection, light emergence with negligible loss of brightness hence diamond looks shiny.
(2) Explain the term absolute refractive index ?
→ When the refraction of light occurs between vacuum and specific medium, then the refractive index in that medium is called as absolute refractive index.
(3) State the difference between real image and virtual image.
→
1 | A real image can be obtained on a screen. | A virtual image cannot be obtained on a screen. |
2. | A real image is inverted with respect to the object. | A virtual image is erect with respect to the object. |
3. | Example: The image of a distant object formed by a concave mirror. | Example: The image of an object formed by a plane mirror or by a convex mirror. |
(4) What is the principle of working of thermos flask .
→ Working principle – glass is poor conductor of heat. The lid of the vessel is also made of a substance which is poor conductor of heat. The glass vessel is covered by cork like substance hence heat cannot flow through it by the process of conduction. The space between two layers of the glass pot is almost free of air hence heat cannot flow by the process of conduction or convection. The radiant heat is also reflected by the shiny surface of the glass wall hence heat loss due to radiation gets minimized. Hence hot substance remains hot and cold substance remains cold.
(5) Explain the term radiation ?
→ The process in which no material medium is required to transmit The heat from a hot substance to the relatively cold surroundings is called as radiation.
(6) What do you mean by convention current?
→ The hottest portion of gas or liquid are lighter and hence move upwards while the colder portion of the gas or liquid flow downward to take that place. They in turn rise when they get warm. This continuous cyclic process results in the formation of current is called as convection current.
(7) What is conduction?
→ The process by which heat flows through a solid surface is called as conduction. The heat flows from hot surface to the colder one. The movement of heat is from hotter to colder surface.
(8) How clouds are formed?
→
- Water evaporates from rivers ponds lakes oceans wet lands and living body. This water vapor mixes with hot air near the earth surface.
- Air which is hot and more humid is lighter done the air which is cool and less humid.
- So hot and you made air moves in upward direction. At higher altitude pressure of air is low. Air expands and cools down.
- Then the point is reached where water vapor in the air condenses to water droplets around the dust particles present in the air.
- The large collection of such water droplets floating in the sky called as clouds.
(9) Write three examples of motion due to electrostatic force ?
→
- The motion of electrons revolving around the nucleus
- In winter the plastic comb attracts pieces of paper after combing.
- In winter, inflated balloon stuck to your sweater.
10.) Define free falling object. And state the laws of free-falling objects.
→ When an object is falling freely towards Earth due to gravitation is called as free-falling object. Galileo States three laws for free falling objects.
- When an objects address is allowed to fall freely from a certain height they fall with the same rapidity.
- Speed of free-falling body increases with increasing time of fall.
- Distance covered by body increases with its time of fall.
Q.(4) Long answer question.
(1) Explain the experiment that shows liquid exerts se pressure on the walls of the container they exist.
→
- We take a plastic bottle and fix a cylindrical glass tube at its bottom
- Heat the end of a glass tube and insert it immediately near the bottom of the plastic bottle.
- Any leakage occurs on the bottle seal it with molten wax.
- Now cover the open end of the glass tube with rubber sheet and fill the bottle with water near to its half.
- Be sure that rubber sheet bulges out due to the pressure applied by water. And hence the liquid exerts pressure on the walls of the container they exist is proved.
(2) The object in motion is easy to move than the static object ?
→ When the object is in motion the contact points on it surface does not get time to lock into the contact points on the floor. Hence it is easier to move the object which is in motion than that of the static object.
(3) Describe two types of friction ?
→
- Static friction – the friction between stationary object and the surface on which it is resting is called static friction.
- Sliding friction – the friction between two surfaces in contact when one of them sliding over the other is called as sliding friction.
(4) Why does white light disperse while passing through glass prism
→ The seven constituent colors are present in white light. The speed of each color is very different. While passing through the glass prism each color deviates by different amounts. Therefore, white light disperses while passing through a prism.
(5) Fill in the blanks.
(1) Mass of the water in the Tumblr is 5 Kg then weight of the water in the Tumblr is ____ .
Ans – 49 N
(2) When an object floats in a liquid, weight the object and weight of the displaced liquid are _______
Ans – same
(3) The earth pulls all objects with ____ force
Ans – gravitational force
(4) Force of gravity on unit mass is numerically equal to ____
Ans – acceleration due to gravity
(5) melting point of gold is _____
Ans – 1063 degree Celsius