885 + Interview Questions in Physics in Class 8 Page 9 InterviewSolution

401.	What is a new moon day?
Answer» Answer :The DAY when moon is not visible is called new moon day.On a new moon day,the moon LIES in between the SUN and the EARTH.

Discussion

402.	Explain why a charged body loses its charge if we touch it with our hand.
Answer» ANSWER :when we TOUCH a charged body with our HAND, it gets discharged because the CHARGE MOVES though our body to the earth.

Discussion

403.	__________Right-hand grip rule is used to find the direction of deflection of a magnetic needle placed near a current carrying conductor.
Answer» ANSWER :AMPERE's

Discussion

404.	A constant immersion hydrometer floats vertically in water when the weight of its float is 30 g. When it is made to float in a liquid (miscible in water), the weight of its float is increased by 10 g. Find the weight of the hydrometer when it is floated in a mixture containing equal masses of water and the liquid.
Answer» Solution :(i) In constant immersion Hydrometer, will the level of the immersion of the hydrometer ramain same (constant) ? FIND the weight of the DISPLACED WATER using law of floatation. Is the volume of the displaced water = Volume of the immersed part of hydrometer `=30 cm^(3)` ? What is the weight of the hydrometer when it floats in the liquid ? By using law of floatation, find the density of the liquid. Since, density of the MIXTURE contains equal masses of liquid and water, so, `rho_("mixture")=(M_(W)+M_(L))/(V_(w)+V_(L))=`? But, `V_(L)=(M_(L))/(D_(L)) " and " V_(w)=(M_(w))/(D_(w))` By applying, find the value of `rho_("mixture")`. Substitute the values in, `W=U=Vrho_("mixture"g)` This gives the weight of the hydrometer. (ii)34.28 g

Discussion

405.	A is a conductingrod connected to acell as shown in the diagram. If 5 A of current passes through the circuit for 5 s, find the amount charge accumulated on 'A'.
Answer» SOLUTION :When current passes through a CONDUCTING rod, accumulation of CHARGE do not TAKE place. Hence, the charge ACCUMULATED on A is zero

Discussion

406.	The S.I. unit of surface charge density is ________ .
Answer» C ` CM^(-2)` A `m^(-2)` A `cm^(-2)` C `m^(-2)` ANSWER :D

Discussion

407.	The types of cells in which it is possible to restore thechemicals are called ___________ .
Answer» ANSWER :SECONDARY CELLS

Discussion

408.	Suppose a car has 4000 J of kinetic energy. What will be its kinetic energy if the speed is doubled? What if the speed is tripled?
Answer» Solution :When speed is doubled , KE will increase FOUR TIMES. Hence, KE=4000 x 4 =16000 J or 16 kJ When the speed is tripled, KE will become nine times. Hence, KE=4000 x 9 = 36000 J or 36 kJ

Discussion

409.	A' can finish certain work in one day and B can finish the same work in two days. The ratio of energy spent by A to that spent by B is ______.
Answer» ANSWER :`1 : 1`

Discussion

410.	Arrange the following statement in sequential order the process of plotting the lines of force around a bar magnet. (a) Draw a line in the middle of a white paper fixed on a drawing board. (b) Repeat the procedures described above, by shifting the compass and plot the points 2,3,4 , etc. (c) Place a bar magnet NS on the line so that its axial line coincides with the line on the paper and mark its boundary. (d) Join the points 0,1,2,3,....by a smooth curve. (e) Take a plotting compass and place it such that its south pole is directed towards point 0 at the edge of the bar magnet, and mark point 1 in the direction in which the north pole of the plotting compass points.
Answer» acebd abced ebcad eabcd Solution :(a) Draw a line in the middle of a white paper fixed on a drawing board. (b) PLACE a bar magnet NS on the line on the paper and mark its BOUNDARY. (C) take a plotting compass and place it such that its south pole is directed TOWARDS point 0 at the edge of the bar magnet and mark point 1 in the direction in which the north pole of the plotting compass points. (d) Repeat the procedure described above by shifting the compass and plot the points 2,3,4. etc. (E) Join the points 0,1,2,3,.... by a SMOOTH curve.

Discussion

411.	If a traveller using a compass needle follows the direction of the magnetic needle, would be able to reach the geographic north pole ? Explain in detail.
Answer» Solution :What is the DIFFERENCE between geographical poles and magnetic poles ? Will the geographical axis COINCIDE with the magnetic axis ? Why ? When a bar magnet is kept NEARER to a magnetic compass it DEFLECTS. Why ?

Discussion

412.	Define Period of rotation.
Answer» Answer :It is the TIME taken by a planet to COMPLETE one ROTATION on its own axis.

Discussion

413.	Which of these is not a lubricant?
Answer» Aircushion Grease Granite Soil Answer :D

Discussion

414.	In the following graphs, the velocity of linearly moving body is against its time of travel.Analyse each of the given graphs and disecus the type of motion of the body
Answer» Solution :(i) Does the velocity of the moving body REMAING constant with time Then FIND the acceleration of the body (II) Can the velocity of the body become infinity at a given instant of time. [(or) can abody have two different velocities at the same time]. Is it possible to find the acceleration of the body? (ii) Does a body undergo equal change in velocity in the equal intervals of time? If yes, then find the type of accelertation of the body . (iv) Find how the velcity of anody changes with time. Is the bodyaccelerated or decerated ? If `a=(v-u)/(t)` is positive, what does it mean? How does the velocity of the body change with time? Then, find whether the body is acceleratd or decelerated. If `a=(v-u)/(t)` is NEGATIVE, what does it mean?

Discussion

415.	State whether the following statements are true or false : In the treatment of cataract, the opaque lens is removed and a new artificial lens is inserted.
Answer» ANSWER :1

Discussion

416.	When a conductor is connected to a source of current, the number of electrons enteringat one end of the conductor is equal to the number of electronsleavingthe conductor fromthe other end, per second
Answer» ANSWER :1

Discussion

417.	Why do gaseous fuels have high calorific values ?
Answer» SOLUTION :(i) REASON for high calorific value of a FUEL. (II) Presence of hydrogen

Discussion

418.	What is meteor shower?
Answer» Answer :When EARTH comes ACROSS the tail of a COMET, a cluster of meteors can be seen. This is CALLED meteor shower. It occurs at REGULAR intervals.

Discussion

419.	Define the following: Angle of incidence
Answer» Answer :Angle of INCIDENCE:The angle between the incident RAY and the NORMAL at the POINT of incidence is known as the angle of incidence.

Discussion

420.	In order to prevent loss of magnetism, ______are used.
Answer» ANSWER :MAGNETIC KEEPERS

Discussion

421.	In which direction would a compass needle point when placed at the centre of the soft iron ring shown in the figure below ? Substantiate your answer with reason
Answer» Solution :(i) What is net magnetic field at the CENTRE of the ring ? (ii) Compare the ABILITY of soft iron to allow the magnetic lines of force to PASS through it with that of air. Which DIRECTION does a magnetic needle point in the absence of an external magnetic field ?

Discussion

422.	A pebble of mass 33 g is lowered into a measuring jar containing water so that it is completely covered in water. The initial level of water was 60 ml and after lowering the stone it was found to be 74 ml. What is the density of stone?
Answer» ANSWER :`2.35 "g/cm"^3`

Discussion

423.	A magnet is dropped vertically downwards along the axis of the Aluminium loop of wire lying horizontally. Will there be any difference in the time of fall if the wire is at room temperature and heated to below its melting point ? If so, explain. (Hint: Resistance of a conductor is directly proportional to its temperature).
Answer» Solution :(i) CHANGE in the magnetic field (II) Dependence of induced current on RESISTANCE of the coil (iii) Dependence of resistance on temperature (iv) Force between induced current and magnet. (v) Dependence of fall in amount of current induced.

Discussion

424.	Stand in the centre of a big room and start rotating.Inwhich direction will the objects in the room appear to move? Do you see them moving in the direction opposite to your motion?
Answer» Answer :Yes,the OBJECTS in the room will appear to MOVE in the DIRECTION opposite to our MOTION.

Discussion

425.	How is water useful in the protection of fruits and vegetables from damage during storage at sub zero temperature?
Answer» Solution :At subzero temperature, does water convert into ICE by loosing heat energy equal to its latent heat of fusion? What ROLE does the SPECIFIC heat capacity of water play. FIND the AMOUNT of (heat energy) latent heat of fusion. Can this energy be used to protect the fruits and vegetables from freezing temperature?

Discussion

426.	In the following figures, state which of the cases is possible, discuss giving reason in each case.
Answer» Solution :(i) PRESSURES at TWO different points in a horizontal surface are equal. (ii) Lower density liquids will float on heavier DENSER liquids. Here, dissimilar non-soluble liquids can seek their own level. Is the pressure at different points inside liquid lying on the same horizontal plane equal ? Find the ratio of the densities of MERCURY and water. Also find the ratio of the HEIGHTS.

Discussion

427.	The frequency of a sound wave is 200 Hz and its wavelength is 150 cm. What is the distance travelled by a sound wave in the time taken to produce 150 waves ?
Answer» SOLUTION :(i) Find the wavelength of the given sound wave. Then, distance traveled by 150 WAVES is `150 (LAMDA)` (II) 225 m

Discussion

428.	The flame of candle or kerosene stove is sometimes yellow and sometimes blue. What do these colours indicate ?
Answer» Solution :(i) Factors AFFECTING the combusting of substance. (ii) ADEQUATE or inadequate supply of OXYGEN or fuel for COMBUSTION. (iii) Complete and incomplete supply of oxygen

Discussion

429.	Explain why objects moving in fluids must have special shape.
Answer» Answer :The force of friction exerted by FLUIDS when an OBJECT is moving through them is CALLED fluid friction or DRAG. Hence, objects moving in fluids must have special shapes to minimise friction and to improve EFFICIENCY between the object and the fluid.

Discussion

430.	The frequency of the ringing of the bell in an electric bell can be altered by______adjustment.
Answer» ANSWER :CONTACT SCREW

Discussion

431.	Why do we reduce friction?
Answer» ANSWER :We REDUCE FRICTION to INCREASE EFFICIENCY.

Discussion

432.	The group of solar cells connected in specific pattern to produce definite potential difference and current is known as____.
Answer» ANSWER :SOLAR PANEL

Discussion

433.	An archer streches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms. muscular, contact,non-contact,gravity, friction, attraction While the arrow moves towards its target, the forces acting on it are due to ______ and that due to ______ of air.
Answer» ANSWER :GRAVITY; FRICTION.

Discussion

434.	An archer streches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms. muscular, contact,non-contact,gravity, friction, attraction The type of force responsible for a change in the state of motion of the arrow is an example of a ______force.
Answer» ANSWER :CONTACT

Discussion

435.	An archer streches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms. muscular, contact,non-contact,gravity, friction, attraction The force applied by the archer to strech the bow is an example of _______ force.
Answer» ANSWER :MUSCULAR

Discussion

436.	An archer streches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms. muscular, contact,non-contact,gravity, friction, attraction To strech the bow, the archer applies a force that cause a change in its _______.
Answer» ANSWER :SHAPE

Discussion

437.	In which of the following devices temporary magnets are used ?
Answer» Dynamo Electric motors Generators Electric cranes Answer :D

Discussion

438.	At constant temperature, when the pressure of a given mass of gas is increased by two times, its volume ____.
Answer» SOLUTION :N//A

Discussion

439.	Fill in the blanks: ____ is an application of chemical effect of electric current.
Answer» ANSWER :ELECTROPLATING

Discussion

440.	Fill in the blanks : The________ contains several nerve cells.
Answer» ANSWER :RETINA

Discussion

441.	Explain how winnowing allows the grain to get separated from the husk.
Answer» SOLUTION :INERTIA of REST of GRAIN is more than inertia of rest of HUSK.

Discussion

442.	The apparent weight of an object on the surface of the moon, if the mass of the object and liquid displaced are X and Y, respectively, is
Answer» `(X-Y)/(G)` `(g)/(6)(x-Y)` `6G(X-Y)` `(6)/(g)(X-Y)` SOLUTION :N//A

Discussion

443.	In the figure shown below if 'D' isa diamanetic substance placed between two strong magnetic poles, map the magnetic lines of force.
Answer» Solution :Is it POSSIBLE to INCREASES the strength of a MAGNET if the maximum number of molecular MAGNETS are arranged in an orderly way ?

Discussion

444.	What is Pole star?
Answer» Answer :POLE star is a star visible TOWARDS the north and remains stationary in the sky with respect to the Earth. It can be located with the HELP of Ursa MAJOR and is not visible from the southern hemisphere.

Discussion

445.	Energy used by maglev trains:
Answer» Solution :What TYPE of ENERGY conversion TAKES PLACES in a magnetic trains ? How is the electrical energy convert into MECHANICAL energy ?

Discussion

446.	In a classroom, if all the students speak together, what would the sound produced be called?
Answer» ANSWER :The sound produced in a classroom when all STUDENTS speak together is CALLED noise

Discussion

447.	Speed of light is __________
Answer» `3xx10^6 km//sec` `3xx10^7 km//sec` `3xx10^5 km//sec` `3xx10^4 km//sec` ANSWER :C

Discussion

448.	Fill in the blanks : A mirror________ the direction of light that falls on it.
Answer» ANSWER :CHANGES

Discussion

449.	What steps should be followed to make buildings and other structures 'Quake Safe'?
Answer» ANSWER :We should CONSULT QUALIFIED ARCHITECTS and engeneers,

Discussion

450.	When two heating devices are used to heat two different substance A and B the heat absorbed by A after 2 seconds is found to be equal to the heat absorbed byy B after 3 seconds. The rise in temperature of A after 5 seconds is found to be equal to the rise in temperature of B after 6 seconds.i the ratio of masses o A and B is 1:2, determine the ratio of the specific heat capacities of two substances.
Answer» Solution :Equate the heat absorbed by A in 2S to that of B in 3s. FIND the ratio of heat SUPPLIED to A and B in unit TIME. find the ratio of heat supplied in 5s to A to heat supplied to B in 6s to determine the ratio of specific heat.

Discussion

Explore topic-wise InterviewSolutions in .

What is a new moon day?

Explain why a charged body loses its charge if we touch it with our hand.

__________Right-hand grip rule is used to find the direction of deflection of a magnetic needle placed near a current carrying conductor.

A is a conductingrod connected to acell as shown in the diagram. If 5 A of current passes through the circuit for 5 s, find the amount charge accumulated on 'A'.

The S.I. unit of surface charge density is ________ .

The types of cells in which it is possible to restore thechemicals are called ___________ .

Suppose a car has 4000 J of kinetic energy. What will be its kinetic energy if the speed is doubled? What if the speed is tripled?

A' can finish certain work in one day and B can finish the same work in two days. The ratio of energy spent by A to that spent by B is ______.

If a traveller using a compass needle follows the direction of the magnetic needle, would be able to reach the geographic north pole ? Explain in detail.

Define Period of rotation.

Which of these is not a lubricant?

In the following graphs, the velocity of linearly moving body is against its time of travel.Analyse each of the given graphs and disecus the type of motion of the body

State whether the following statements are true or false : In the treatment of cataract, the opaque lens is removed and a new artificial lens is inserted.

When a conductor is connected to a source of current, the number of electrons enteringat one end of the conductor is equal to the number of electronsleavingthe conductor fromthe other end, per second

Why do gaseous fuels have high calorific values ?

What is meteor shower?

Define the following: Angle of incidence

In order to prevent loss of magnetism, ______are used.

In which direction would a compass needle point when placed at the centre of the soft iron ring shown in the figure below ? Substantiate your answer with reason

A pebble of mass 33 g is lowered into a measuring jar containing water so that it is completely covered in water. The initial level of water was 60 ml and after lowering the stone it was found to be 74 ml. What is the density of stone?

Stand in the centre of a big room and start rotating.Inwhich direction will the objects in the room appear to move? Do you see them moving in the direction opposite to your motion?

How is water useful in the protection of fruits and vegetables from damage during storage at sub zero temperature?

In the following figures, state which of the cases is possible, discuss giving reason in each case.

The frequency of a sound wave is 200 Hz and its wavelength is 150 cm. What is the distance travelled by a sound wave in the time taken to produce 150 waves ?

The flame of candle or kerosene stove is sometimes yellow and sometimes blue. What do these colours indicate ?

Explain why objects moving in fluids must have special shape.

The frequency of the ringing of the bell in an electric bell can be altered by______adjustment.

Why do we reduce friction?

The group of solar cells connected in specific pattern to produce definite potential difference and current is known as____.

In which of the following devices temporary magnets are used ?

At constant temperature, when the pressure of a given mass of gas is increased by two times, its volume ____.

Fill in the blanks: ____ is an application of chemical effect of electric current.

Fill in the blanks : The________ contains several nerve cells.

Explain how winnowing allows the grain to get separated from the husk.

The apparent weight of an object on the surface of the moon, if the mass of the object and liquid displaced are X and Y, respectively, is

In the figure shown below if 'D' isa diamanetic substance placed between two strong magnetic poles, map the magnetic lines of force.

What is Pole star?

Energy used by maglev trains:

In a classroom, if all the students speak together, what would the sound produced be called?

Speed of light is __________

Fill in the blanks : A mirror________ the direction of light that falls on it.

What steps should be followed to make buildings and other structures 'Quake Safe'?