885 + Interview Questions in Physics in Class 8 Page 10 InterviewSolution

451.	Recall some of your experiences. A ball rolling along the ground gradually slows down and finally comes to rest. When we stop pedalling a bicycle, it gradually slows down and finally comes to rest once its engine is switched off. Similarly, a boat comes to rest if stop rowing it. Can you add some more such experiences? What causes a change in their state of motion? Can you guess the direction in which the force must be acting in each case?
Answer» Answer :Some more such experiences are :(i) A FAN stops moving when the switch is turned off.(II) A top stops moving after ROTATING on the floor for sometime.

Discussion

452.	A person, sitting in a car, tries to move the car by applying force to its walls. Will the car move? Explain in detail.
Answer» SOLUTION :An internal FORCE does not PRODUCE an acceleration. Only EXTERNAL force produces an acceleration.

Discussion

453.	Assertion : When a bar magnet is freely suspended, it points in the north-south direction. Reason : The earth behaves as a magnet with the magnetic field pointing approximately from the geographic south to north.
Answer» ANSWER :SOUTH POLE

Discussion

454.	What is meant by frequency of oscillation?
Answer» Answer :The number of COMPLETE oscillations or to and FRO MOVEMENT produced by an object PER second is called the FREQUENCY of oscillation or frequency.

Discussion

455.	How do we see luminous objects?
Answer» Answer :When LIGHT from LUMINOUS OBJECTS such as sun, FIRE, etc. falls on our eyes, we can seethe objects.

Discussion

456.	What is an earthquake?
Answer» Answer :The suddend shaking or TREMBLING of the EARTH which occurs for a very short time is called earthquake.

Discussion

457.	By increasing the number of turns in the coil, the strength of the magnetic field.
Answer» Solution :What happens to the total length of the wire when the NUMBER of turns PER unit length is INCREASED. What are the factors affecting the STRENGTH of the magnetic FIELD and how are they related ?

Discussion

458.	A train moving at a speed of 100 ms^(-1) comes to rest in 5 seconds. Find its retardation.
Answer» Solution : In VELOCITY of the train `u=100 ms s^(-1)` Final velocity of the train, `v=0 m s^(-1)` Time TAKEN by the ratio to come to rest, `t=5s` `:.` ACCELERATION of the train, `a=(v-u)/(t)=(0.100)/(5)=-20 ms^(-2)` Hence, retradatio of the train `=20 m s^(-2)`

Discussion

459.	Natural magnets are stronger than artificial magnets.
Answer» ANSWER :F

Discussion

460.	Richter scale is not linear. What does it indicate?
Answer» Answer :When we say that the Richter SCALE is not LINEAR, it INDICATES that the MEASURES on the scale are not SIMPLE.

Discussion

461.	Fill in the blanks : _________ and frequency are the two important properties of sound.
Answer» ANSWER :A::D

Discussion

462.	If the refractive index of ice is 1.31, what will be the speed of light in it?
Answer» ANSWER :`2.29xx10^8` m/s

Discussion

463.	Life is known to exist only on ________.
Answer» Venus Earth Mars Jupiter Answer :B

Discussion

464.	When an iron bar is moved over a bar magnet along its length the attractive force______
Answer» INCREASES FIRST and then decreases decreases first and then increases remains same increases Answer :B

Discussion

465.	Find the ratio of time periods of two pendula whose lengths are in the ratio 1 : 4
Answer» SOLUTION :`(T_(1))/(T_(2)) = sqrt((l_(1))/(l_(2))) = sqrt((1)/(4)) = (1)/(2) RARR T_(1) : T_(2) = 1:2`

Discussion

466.	An effort applied on the small piston of a hydraulic jack lifts the load through a distance of 50 cm and the effort is displaced through 2 m. If the diameter of the larger piston is 28 cm, calcualte the area of the cross section of the smaller piston.
Answer» SOLUTION :`d_(1)=50 CM` `THEREFORE M.A. (L)/(E )=(d_(E ))/(d_(L))=(2)/(0.5)=4` `4=(pi_(2)^(2))/(pi r_(1)^(2))` `4=((22)/(7)xx0.14xx0.14)/(A_(1))` `A_(1)=0.0154`

Discussion

467.	Mark the following statements as true (T) or false (F) . Constellation Orion can be seen only with a telescope.
Answer» ANSWER :F

Discussion

468.	If the speed of light in diamond is 1.24xx10^8 m/s, find its refractive index.
Answer» ANSWER :2.42

Discussion

469.	State whether the following statements are true or false: The longer lead of the LED is connected to the positive terminal of the battery and the shorter lead is connected to the negative terminal of the battery.
Answer» ANSWER :1

Discussion

470.	What is inaudible sound?
Answer» Answer :SOUNDS having frequency less than 20 Hz or more than 20,000 Hz cannot be HEARD by human EARS. It is called inaudible SOUND.

Discussion

471.	Quantity of heat gained by 100 kg of iron in raising its temperature by 10^(@)C is 11xx10^(4)cal. If a heater can supply heat at the rate of 1000 J s^(-1), how much time does it take to heat an iron block of mass 2.5 kg when the mecury level in a Fahrenheit thermometer rises by 45 divisions.
Answer» Solution :Find the mass of the iron from GIVEN data. Find the amoun of heat gained by iron to RAISE its temperature by `10^(@)C`, from the given data. Find the specific heat of the iron fro the formula, `Q=msDeltatheta` find the corresponding temperature change in CELSIUS scale, when there is temperature change of 45 divisions in Fahrenheit scale from the formula `(DeltaC)/(100)=(DeltaF)/(180)` . . .(1) Fdin how much amount of heat energy 'Q' is REQUIRED for 2.5 kg iron block to increase its temperatrue by `'DeltaC'` makeuse of `Q'=2.5xxsxxDeltaC`. . .(2) Check the units of Q' If it in calorie, convert it into joule. then, find the amount of time taken to PRODUCE Q' by dividing Q' by 1000.

Discussion

472.	A physics teacher has a weight of 700 N. What pressure does he exert on the ground if his feet have an area of 0.025 m^2 each?(Remember, he has two feet!)
Answer» SOLUTION :Weight =Force = 700 N Total area = `0.50 m^2` Pressure = `700 N//0.050 m^2` = 14000 PA

Discussion

473.	Fill in the blanks. Friction opposes the _________ between the surfaces in contact with each other.
Answer» ANSWER :RELATIVE MOTION

Discussion

474.	A constant external force acts on a body in motion. If the mass of the body is doubled with the force remaining the same, its acceleration also doubles.
Answer» ANSWER :FALSE

Discussion

475.	_________is the brightest planet in the night sky.
Answer» Jupiter Mars Saturn Venus Answer :D

Discussion

476.	Magnetic lines of force around a current carrying conductor are circular.
Answer» ANSWER :1

Discussion

477.	Name two materials that can conduct electricity.
Answer» ANSWER :two metals like COPPER and aluminium can conduct ELECTRICITY.

Discussion

478.	Fill in the blanks : Any celestial body revolving around another celestiai body is called its __________
Answer» ANSWER :SATELLITE

Discussion

479.	In a telegraph______is connected to positive terminal of a battery and the negative terminal of the battery is connected to__________
Answer» ANSWER :MORSE KEY, EARTH

Discussion

480.	What happens when you open the mouth of an inflated balloon?
Answer» ANSWER :When we open the MOUTH of an INFLATED balloon, it GETS deflated.

Discussion

481.	What are the properties of electrostatic force?
Answer» ANSWER :When a charge BODY is brough NEAR an uncharged body, it attract OTHERS.

Discussion

482.	A ball is thrown vertically upward.If it spend 4s in air,then find the maximum height achieved by it.
Answer»

Discussion

483.	In a tsunami the shock waves originating in the ocean bed propagate
Answer» as TRANSVERSE WAVES only as LONGITUDINAL waves only as both transverse and longitudinal waves Neither as transverse nor as longitudinal waves Answer :C

Discussion

484.	Fill in the blanks : All the stars appear to revolve around the _________
Answer» ANSWER :POLE STAR

Discussion

485.	In Which of the following devices is a permanent magnet not used ?
Answer» Electric MOTOR Telegraph Generators Particle accelerators. Solution :Permanent magnets are USED in electric motor, GENERATOR and particle accelerator. An ELECTROMAGNET, which is a temporary magnet, is used in telegraph system.

Discussion

486.	You have learnt class VII that strong winds during a storm or a cyclone can blow away even the roof - tops. You also learnt that winds and cyclones are caused by the differences in air pressure. Is there any relation between pressure and force?
Answer» ANSWER :YES, PRESSURE and FORCE are RELATED to each other.

Discussion

487.	I learnt in class VI that a magnet attracts a piece of iron towards it. Is attraction also a pull? What about repulsion between similar poles of two magnets? Is it a pull or a push?
Answer» ANSWER :Yes, ATTRACTION by magnet is also a PULL.Yes, attrsction between a piece of IRON and a magnet is also a pull.

Discussion

488.	The unit of calorific value is Jg^(-1) .^(@)C^(-1).
Answer» ANSWER :F

Discussion

489.	A constant immersion hydrometer weighing 20 g sinks upto mark 'x' in water and this hydrometer has to weight 25 g to mark 'x' in a given liquid. Then the relative density of the liquid is ____.
Answer» 0.25 1.25 0.75 `2.00` SOLUTION :`R.D.=("WEIGHT of HYDROMETER in liquid")/("weight of hydrometer in WATER")` `=(25)/(20)=1.25`

Discussion

490.	A coil is moved towards a stationary magnet. The voltage induced in the coil depends on____________
Answer» area of the COIL the speed with which the coil is moved towards the bar magnet. number of TURNS of the coil All the above Answer :D

Discussion

491.	What is the charge acquired by a glass rod when it is rubbed with silk?
Answer» ANSWER :When a GLASS rod is RUBBED with SILK, it acquires a positive CHARGE.

Discussion

492.	The heat produced on complete combustion of 20 g of a fuel could raise the temperature of 1.5 kg of water form 25^(@)C to 75^(@)C. Calculate the calorific value of the fuel if the specific heat capacity of water is 4.2 J g^(-1).^(@)C^(-1). Assume that the heat absorbed by the container is negligible.
Answer» Solution :(i) Formula for calorfic value, Q=`msDeltatheta`. (ii) Find the amount of heat energy required to INCREASES the temperature of 1.5 `mug` of water from `25^(@)C` to `75^(@)C` using the formula Q=ms ...(i) Let 's' denote specific heat capacity of water and `'Delta theta'` denote change in the temperature. Is this heat energy RELEASED due to COMPLETE combustion of 20 g of a fuel ? Then, the formula related to combustion of fuel is Q=m.K. ....(2) Q=m.k =mwst, since heat released in combustion is absorbed by water. Thus, find the value of 'k' (iii) `15.75 kJ g^(-1)`

Discussion

493.	What are the safety measures to be followed during lightning and thunderstorm?
Answer» Answer :We should FIND a SHELTER or a CLOSED indoor space LIKE a house or a BUILDING.

Discussion

494.	If the focal lenght of a convex mirror is 12 cm, what would be its radius of curvature?
Answer» ANSWER :24 CM

Discussion

495.	State whether the following statements are true orfalse : Fluid friction is also known as drag.
Answer» ANSWER :1

Discussion

496.	Fill in the blanks : _________of it-regularities between two surface in contact causes friction.
Answer» ANSWER :INTERLOCKING

Discussion

497.	Instrument (s) capable of producing musical notes is/are _____
Answer» viola oboe cello All the above Answer :D

Discussion

498.	Fill in the blanks : Saturn appears _________ in colour.
Answer» ANSWER :YELLOWISH

Discussion

499.	As an air bubble comes from the bottom of a lake to the top, its radius "_____"
Answer» the PRESSURE exerted by WATER on the bubble decreases as the height of the water COLUMN above it decrease. the density of water INCREASES as we move downwads. at constant temperature, pressure inside the AIR bubble are volume of the bubble inversely proportional to each other. Both 1 and 3 Solution :N//A

Discussion

500.	Why do fountains of water rush out of the leaking joints or holes in pipes supplying water?
Answer» Answer :FOUNTAINS of WATER RUSH out of the leaking joints or holes in pipes supplying water DUE to the pressure excerted by water on the WALLS of the pipe.

Discussion

Explore topic-wise InterviewSolutions in .

A person, sitting in a car, tries to move the car by applying force to its walls. Will the car move? Explain in detail.

Assertion : When a bar magnet is freely suspended, it points in the north-south direction. Reason : The earth behaves as a magnet with the magnetic field pointing approximately from the geographic south to north.

What is meant by frequency of oscillation?

How do we see luminous objects?

What is an earthquake?

By increasing the number of turns in the coil, the strength of the magnetic field.

A train moving at a speed of 100 ms^(-1) comes to rest in 5 seconds. Find its retardation.

Natural magnets are stronger than artificial magnets.

Richter scale is not linear. What does it indicate?

Fill in the blanks : _________ and frequency are the two important properties of sound.

If the refractive index of ice is 1.31, what will be the speed of light in it?

Life is known to exist only on ________.

When an iron bar is moved over a bar magnet along its length the attractive force______

Find the ratio of time periods of two pendula whose lengths are in the ratio 1 : 4

An effort applied on the small piston of a hydraulic jack lifts the load through a distance of 50 cm and the effort is displaced through 2 m. If the diameter of the larger piston is 28 cm, calcualte the area of the cross section of the smaller piston.

Mark the following statements as true (T) or false (F) . Constellation Orion can be seen only with a telescope.

If the speed of light in diamond is 1.24xx10^8 m/s, find its refractive index.

State whether the following statements are true or false: The longer lead of the LED is connected to the positive terminal of the battery and the shorter lead is connected to the negative terminal of the battery.

What is inaudible sound?

Quantity of heat gained by 100 kg of iron in raising its temperature by 10^(@)C is 11xx10^(4)cal. If a heater can supply heat at the rate of 1000 J s^(-1), how much time does it take to heat an iron block of mass 2.5 kg when the mecury level in a Fahrenheit thermometer rises by 45 divisions.

A physics teacher has a weight of 700 N. What pressure does he exert on the ground if his feet have an area of 0.025 m^2 each?(Remember, he has two feet!)

Fill in the blanks. Friction opposes the _________ between the surfaces in contact with each other.

A constant external force acts on a body in motion. If the mass of the body is doubled with the force remaining the same, its acceleration also doubles.

_________is the brightest planet in the night sky.

Magnetic lines of force around a current carrying conductor are circular.

Name two materials that can conduct electricity.

Fill in the blanks : Any celestial body revolving around another celestiai body is called its __________

In a telegraph______is connected to positive terminal of a battery and the negative terminal of the battery is connected to__________

What happens when you open the mouth of an inflated balloon?

What are the properties of electrostatic force?

A ball is thrown vertically upward.If it spend 4s in air,then find the maximum height achieved by it.

In a tsunami the shock waves originating in the ocean bed propagate

Fill in the blanks : All the stars appear to revolve around the _________

In Which of the following devices is a permanent magnet not used ?

You have learnt class VII that strong winds during a storm or a cyclone can blow away even the roof - tops. You also learnt that winds and cyclones are caused by the differences in air pressure. Is there any relation between pressure and force?

I learnt in class VI that a magnet attracts a piece of iron towards it. Is attraction also a pull? What about repulsion between similar poles of two magnets? Is it a pull or a push?

The unit of calorific value is Jg^(-1) .^(@)C^(-1).

A constant immersion hydrometer weighing 20 g sinks upto mark 'x' in water and this hydrometer has to weight 25 g to mark 'x' in a given liquid. Then the relative density of the liquid is ____.

A coil is moved towards a stationary magnet. The voltage induced in the coil depends on____________

What is the charge acquired by a glass rod when it is rubbed with silk?

What are the safety measures to be followed during lightning and thunderstorm?

If the focal lenght of a convex mirror is 12 cm, what would be its radius of curvature?

State whether the following statements are true orfalse : Fluid friction is also known as drag.

Fill in the blanks : _________of it-regularities between two surface in contact causes friction.

Instrument (s) capable of producing musical notes is/are _____

Fill in the blanks : Saturn appears _________ in colour.

As an air bubble comes from the bottom of a lake to the top, its radius "_____"

Why do fountains of water rush out of the leaking joints or holes in pipes supplying water?

In a telegraphis connected to positive terminal of a battery and the negative terminal of the battery is connected to____