885 + Interview Questions in Physics in Class 8 Page 7 InterviewSolution

301.	When only a small portion of the moon appears in the sky, it is known as
Answer» FULL moon new moon crescent moon half moon Answer :C

Discussion

302.	How much force is applied on the body when 780 J of work is done in displacing the body through a distance of 30 m in the direction of force?
Answer» ANSWER :26 N

Discussion

303.	An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?
Answer» ANSWER :An inflated balloon when rubbed with a piece of SYNTHETIC cloth ACQUIRES some CHARGE.

Discussion

304.	Two wires, A and B are placed parallel to each other in a vertical plane such that A carries 5 A and B carries 2 A of current in W-E direction. If a magnetic compass is placed mid way between A and B such that it is free to rotate in horizontal plane, then in which direction, would it deflect ? if the direction of current in A and B is reserved, in which direction would it deflect ?
Answer» Solution :(i) RELATIONS between strength of current and magnetic field. (ii) USE Ampere's right hand rule to find the direction of magnetic field. (iii) Usually to determine the magnetic MERIDIAN we use a magnetic compass and the magnetic needle INSIDE it is fixed in a horizontal plane.

Discussion

305.	My grandmother told me that the earth is balanced on the horn of a bull and when the bull shifts it to the other horn, an earthquake takes place. How could it b e true?
Answer» ANSWER :It is not true that the earth is balaced on the HORN of a bull and when the bull SHIFTS it to the other horn, an EARTHQUAKE takes place. It is a myth.

Discussion

306.	When the coils of an electric generator rotate in a megnatic field,
Answer» the mechanical ENERGY change into electric energy. the thermal energy changes into electric energy. the SOLAR energy changes into electric energy the WIND energy changes into electric energy. Answer :A

Discussion

307.	In a transverse wave, the time interval between 1st crest and 11th crest is 50s, then the time period of the wave is _____
Answer» 5s 10 s 20 s 2 s Answer :A

Discussion

308.	The amount of force to be applied on the spanner at a length of 0.25 m from the bolt is 400 N. Find the torque to open a bolt.
Answer» ANSWER :100 NM

Discussion

309.	Following are down the steps of an experiment to prove that medium is required for the propagation of sound waves. Arrange these steps in propagation of sound waves. Arrange these steps in proper sequence (a) Consider a glass jar with an outlet connected to a vacuum pump and a closed lid (b) Suspend an electric bell. (c) Evacuate the jar by using a vaccum pump (d) Switch on the electric bell (e) Observe that the intensity of the sound is less when the jar is evacuated (f) This proves that medium is required for the propagation of sound
Answer» f E d a b c a b d e c f a b d c e f a b c d e f Solution :Take a GLASS jar with CLOSED lid and an outlet connected to a vaccum pump (a) Suspend an electric bell (b) and switch it on (d) Now EVACUATE the jar (c) and observe that intensity of sound is DECREASED when the jar is evacuated (e). This proves that a medium is required for the propagation of sound (f)

Discussion

310.	The charge supplied to a good conductor always resides
Answer» at the suppliedposition itself. on its OUTER surface. inside the body. All the above. Answer :B

Discussion

311.	What is a full moon day?
Answer» Answer :FULL moon day is the day when the ILLUMINATED Part of the moon appears as an ENTIRE circle in the sky when the EARTH is between the SUN and the moon.

Discussion

312.	What is Alpha Centauri?
Answer» ANSWER :Alpha Centauri is the star NEAREST to the EARTH after the Sun. It is situated at a DISTANCE of about 4.3 light years.

Discussion

313.	The polarity of an electromagnet can be changed by changing the direction of electric current through the coil.
Answer» ANSWER :T

Discussion

314.	Fill in the blanks in the following. A person 1 m in front of a plane mirror seems to be________ m away from his ímage.
Answer» ANSWER :2

Discussion

315.	If the radius of curvature of a concave mirror is 22 cm, what would be its focal length?
Answer» ANSWER :11 CM

Discussion

316.	Two cylinderical bodies 'A' and 'B' have their radii in the ratio of 1:2 and their lengths are in the ratio of 3:2. When equal amount of heat energy is supplied to them, the rise in the temperature of A is found to be double the rise in temperature of B. Determine the ratio of their specific heat capacity. The ratio of density of A and B is 3:1
Answer» Solution :Compare the HEAT abosrbed by A and B `Q=msDeltat` But mass=density`xx`volume And volumej=length`xx`AREA of cross SECTION.

Discussion

317.	Statement-1 : Combustion or burning takes place only in the presence of oxygen. Statement-2: Oxygen is supporter for combustion.
Answer» STATEMENT (1) and (2) are TRUE Statement (1) is true and statement (2) is FALSE Statement (1) and (2) are false Statement (1) is false and statement (2) is true. Answer :D

Discussion

318.	The total distance between the lower fixed point and the upper fiixed point of a thermometer is 12 cm. when this thermometer is palced in a vessel containing 500g water the reading on the scale was 3 cm.. When 10 lead shots at 100^(@)C were dropped into this container the mercury level int he thermometer rose to 31 mm. find the average heat capacity o the lead shots. (you may leave the answer as a fraction). Specific heat capacity of water =4.2 kJ kg^(-1)" "K^(-1)
Answer» Solution :12 CM`=100^(@)C` 3cm`=x^(@)C` 31mm`=y^(@)C` Find x and y. Rise in temperature of water=1nm=`(y-x)K` Heat gained/lost, `Q=mxxsxxDeltatheta` Heat capacity `H=mxxs` `therefore` Heat lsot by theh hot body `=HxxDeltatheta_("lead shots")` `=H(100-y)` Calculate the heat gained by the cold water. LET this be Q. Find, `H=(Q)/(100-y)` If N is the numbe of leads shots. Average heat capacity `=(Q)/(N(100-y))`

Discussion

319.	The strength of magnetic field due to a straight current carrying conductor, at a given distance increases with increase in the
Answer» TEMPERATURE of the conductor length conductor strength of the current Both (a) and (C) ANSWER :C

Discussion

320.	Fill in the blanks : Bifocal lenses, contact lenses, tinted lenses, magnifiers and telescopic aids are________ aids.
Answer» ANSWER :OPTICAL

Discussion

321.	Make two toy telephones. Use them as shown in Fig. 13.20. Make sure that the two strings are taut and touch each other. Let one of you speak. Can the remaining three persons hear? See how many more friends you can engage in this way. Explain your observations.
Answer» Answer :Yes, the remaining three persons can ALSO hear.As sound can TRAVEL through a MEDIUM, in this case sound is TRAVE ling through the STRING and thus everyone on the toy telephone can hear the voice.

Discussion

322.	Do you recall how we can decide whether an object is moving faster than the order?
Answer» Answer :We can decide WHETHER an object is moving faster than the order object by comparing the DISTANCE COVERED by the TWO object in a unit time.

Discussion

323.	Fill in the blanks : Friction is caused by ________between the two surfaces in contact.
Answer» ANSWER :IRREGULARITIES

Discussion

324.	If F_(CS), F_(CL), F_(CG) represents cohesive force of solids, cohesive force of liquid and cohesive force of gases, then the choose the correct answer.
Answer» `F_(CS)=F_(CL)= F_(CG)` `F_(CS) gt F_(CL) gt F_(CG)` `F_(CS) LT F_(CL) lt F_(CG)` `F_(CS) gt F_(CL) = F_(CG)` Solution :`F_(CS) gt F_(CL) gt F_(CG)` As the molecules is SOLIDS are closely packed COMPARED to liquid and compared to GASES, the cohesive force of solid `gt ` cohesive force of liquid `gt` cohesive in gas.

Discussion

325.	You are aware that a plane mirror forms only a single image of an object. What happens if two plane mirrors are used in combination?
Answer» ANSWER :If TWO PLANE mirrors are used in combination, at DIFFERENT angles, a NUMBER of images are formed.

Discussion

326.	What is the length of vocal cords in men and women?
Answer» Answer : The LENGTH of VOCAL cords in men is about 20 MM and that in women is about 5 mm SHORTER than men.

Discussion

327.	An office safe has a weight of 800 N. If the area of the base is 1.25 m^2, what is the pressure on the floor of the office?
Answer» ANSWER :640 PA

Discussion

328.	Two identical flasks - one filled with water to the "500 cm"^3 mark, and the other filled with kerosene to the same "500 cm"^3 mark are measured on an electronic balance. The flask filled with water is found to weigh 620 g, and that filled with kerosene weighs 520 g. The empty flask is measured and found to be 120 g. Find the densities of water and kerosene.
Answer» SOLUTION :Volume of water = `"500 cm"^3` Mass of empty beaker = 120 G Mass of water = 620-120 = 500 g DENSITY of water = M/V `= "500 g/500 cm"^3 = 1 "g/cm"^3` Volume of kerosene = `500 "cm"^3` Mass of kerosene = 520-120 =400 g Density of kerosene = M/V = 400/500 = 0.8 `"g/cm"^3`

Discussion

329.	In which part of the sky can you find Venus if it is visible as an evening star?
Answer» Answer :lf Venus is VISIBLE as an EVENING star,then it is visible in the WESTERN SKY.

Discussion

330.	What do you mean by Iateral inversion?
Answer» ANSWER :Lateral inversion is the phenomenon of FORMATION of image by a plane mirror when the right hand SIDE ofan object appears to be the left hand side and VICE versa.

Discussion

331.	Choose the correct option (Multiple choice questions) : Which among the following has white light?
Answer» Fire Laser Tubelight Sunlight Answer :D

Discussion

332.	A brick measures 12 cm xx 6 cm xx 3 cm. Initially, it is kept on the ground such that the rectangular surface with the smallest area is in contact with the ground and then it is placed such that the rectangular surface with the largest area touches the ground. Calculate the height of the centre of gravity from the ground in the two cases. Out of the two positions, in which case does the brick have greater stability and why?
Answer» Solution :(i) In first case HEIGHT of the brick = 12 CM Height fo CG from the ground = 6 cm (i) In second case Height of the brick = 3 cm Height of CG from the ground = 1.5 cm In the second case the brick has more stability because height of CG is small and also BASE area is more.

Discussion

333.	Determine the torque on a bolt, if you are pulling with a force of 250 N directed perpendicular to a wrench of length 20 cm.
Answer» ANSWER :50 NM

Discussion

334.	Do gases also excert pressure? Do they also exert pressure on the walls of their containers?
Answer» ANSWER :YES, GASES ALSO excert PRESSURE.

Discussion

335.	Find the force that produces a pressure of 20 kPa on an area of 0.20 m^2?
Answer» ANSWER :4000 N

Discussion

336.	The time in seconds taken for 20 oscillations noted down in an simple pendulum experiment are 38.6, 40.0, 41.5, 42.8 and 39.4, the time period of the given simple pendulum is ____ s
Answer» `2.5` `2.2` `2.0` `10.1` SOLUTION :`T = (38.6 + 40 + 41.5 + 42.8 + 39.4)/((5)/(20))` `= 2.023s ~~ 2S`

Discussion

337.	If the distance between two successive crests of a wave is 12 cm, then the distance between two successive troughs is ___
Answer» 24 cm 6 cm 12 cm 4 cm Answer :C

Discussion

338.	Find the amount of heat enegy required to convert 100 g of ice at -10^(@)C into stea at 120^(@)C. (Take S_(ice)=0.5" cal "g^(-1).^(@)C^(-1),S_(W)=1" cal "g^(-1)^(@)C^(-1),S_("Steam")=0.5" cal "g^(-1).^(@)C,L_(f)=80" cal "g^(-1),L_(V)=540" cal "g^(-1))
Answer» Solution :Mass of ice=100g. TEMPERATURE of ice, `t_(1)=-100` `.^(@)C`. `S_(ice)=0.5" cal "g^(-1).^(@)C^(-1):L_(f)=80" cal "g^(-1)` `S_(W)=1" cal "g^(1).^(@)C^(-1):L_(V)=540cal" cal "g^(-1)` `S_("steam")=0.5" cal "g^(-1).^(@)C^(-1)`: amount of heat supplied to is `Q=M" "M_(ice)(Deltat)` `Q_(1)=100xx0.5xx[0-(10)]=100xx0.5xx10=500` cal The amount of heat supplied to convert ice into WATER at `0.^(@)C` is `Q_(2)=ML_(F)=100xx80=8000cal` The amount OFHEAT supplied to increase the temperature of water from `0.^(@)C` to `100.^(@)C` is. `Q_(3)=MS_(W)Deltat=100xx1xx(100-0)`

Discussion

339.	What will happen if two surfaces in contact are pressed harder?
Answer» The FORCE of FRICTION will increase The force of friction will reduce There is no effect on FRICTIONAL force None of these Answer :B

Discussion

340.	What is audible sound?
Answer» Answer :Sound which can be heard by human ears is CALLED AUDIBLE sound. Its FREQUENCY RANGES from 20 HZ to 20,000 Hz.

Discussion

341.	Arrange the following statement is sequential order to magnetize a steel bar using single touch method. (a) Once, it has reached the other end, lift the magnet away from the steel bar and again bring it to the starting point. (b) Keep a steel bar to be magnetized ona wooden table. (c) Take a strong magnet and bring one of the poles of the magnet near one end of the steel bar and gently rub from one end to the other end. (d) Repeat this process several times.
Answer» bcad bacd cbda cabd Solution :(a) Keep a steel bar to be magnetized on a WOODEN table (b) (b) Take a strong MAGNET and bring one of the poles of the magnet NEAR one END of the steel bar and gently rub from one end to the other end (c) (c) Once, it has reached the other end, LIFT the magnet away from the steel bar and again bring it to the starting point (a) Repeat this process several times (d)

Discussion

342.	State whether the following statement are true or false : Earthquakes occurs at a time all over the earth.
Answer» ANSWER :1

Discussion

343.	On a certain scale of temperature, the freezing and boiling points of water are maked as 20 and 180 degress, respectively. What is the temperature of a patient suffering with a high fever of 104^(@)F on that scale?
Answer» Solution :What are the LFP and UFP for Fahrenheit scale ? Now for given scale of TEMPERATURE, take LFP and UFP as `20^(@)` and `180^(@)`. The, take CORRESPONDING temperature of `104^(@)F` as 'T' in the given scale. Find the value of 'T' from the FORMULA `(T-LFP)/(UFP-LFP)=`constant.

Discussion

344.	If the percentage decrease in the length of a simple pendulum is 10%, then find the percentage decrease in its time period
Answer» Solution :(i) `l_(2) = l_(1) -10% " of " l_(1), (T_(1))/(T_(2)) = SQRT((l_(1))/(l_(2))), (T_(1) - T_(2))/(T_(1)), xx 100` (ii) 5%

Discussion

345.	Calculate the pressure in the following cases : (i)On the surface ofa block , if it weighs 60 N and is lying on a side with area 0.3 m x 0.1 m. (ii)On the same 60 N block , if it is lying on a side with area 0.1 m x 0.2 m .
Answer» Solution :i. Pressure =Force/AREA =60 N / (0.3 m x 0.1 m) =`60 N // (0.03 m^2)`= 2000 Pa II. Pressure = Force/Area =60 N / (0.1 m x 0.2 m) `=60//0.02 m^2`= 3000 Pa Therefore , we notice that for the same force , pressure INCREASES as area DECREASES .

Discussion

346.	What do you do to make a football move?
Answer» ANSWER :We KICK a FOOTBALL to MAKE it MOVE.

Discussion

347.	To increase the stability of a ship
Answer» the base area should be MADE large height of its centre of GRAVITY should be KEPT as LOW as possible Both (a) and (b) Neither (a) nor (b) Answer :C

Discussion

348.	If the speed of light in air is 3 xx 10^8 m/s, and the refractive index of water is 1.33, find the speed of light in water.
Answer» ANSWER :`2.25xx10^8` m/s

Discussion

349.	Choose the correct option (Multiple choice questions) : The size of the pupil is controlled by the________.
Answer» iris retina cornea lens Answer :A

Discussion

350.	What is the mass of air in a room measuring 10.0 m x 5.2 m x 2.5 m, if the density of air is 1.3 kg//m^3 ?
Answer» ANSWER :169 KG

Discussion

Explore topic-wise InterviewSolutions in .

When only a small portion of the moon appears in the sky, it is known as

How much force is applied on the body when 780 J of work is done in displacing the body through a distance of 30 m in the direction of force?

An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

My grandmother told me that the earth is balanced on the horn of a bull and when the bull shifts it to the other horn, an earthquake takes place. How could it b e true?

When the coils of an electric generator rotate in a megnatic field,

In a transverse wave, the time interval between 1st crest and 11th crest is 50s, then the time period of the wave is _____

The amount of force to be applied on the spanner at a length of 0.25 m from the bolt is 400 N. Find the torque to open a bolt.

The charge supplied to a good conductor always resides

What is a full moon day?

What is Alpha Centauri?

The polarity of an electromagnet can be changed by changing the direction of electric current through the coil.

Fill in the blanks in the following. A person 1 m in front of a plane mirror seems to be________ m away from his ímage.

If the radius of curvature of a concave mirror is 22 cm, what would be its focal length?

Statement-1 : Combustion or burning takes place only in the presence of oxygen. Statement-2: Oxygen is supporter for combustion.

The strength of magnetic field due to a straight current carrying conductor, at a given distance increases with increase in the

Fill in the blanks : Bifocal lenses, contact lenses, tinted lenses, magnifiers and telescopic aids are________ aids.

Make two toy telephones. Use them as shown in Fig. 13.20. Make sure that the two strings are taut and touch each other. Let one of you speak. Can the remaining three persons hear? See how many more friends you can engage in this way. Explain your observations.

Do you recall how we can decide whether an object is moving faster than the order?

Fill in the blanks : Friction is caused by ________between the two surfaces in contact.

If F_(CS), F_(CL), F_(CG) represents cohesive force of solids, cohesive force of liquid and cohesive force of gases, then the choose the correct answer.

You are aware that a plane mirror forms only a single image of an object. What happens if two plane mirrors are used in combination?

What is the length of vocal cords in men and women?

An office safe has a weight of 800 N. If the area of the base is 1.25 m^2, what is the pressure on the floor of the office?

In which part of the sky can you find Venus if it is visible as an evening star?

What do you mean by Iateral inversion?

Choose the correct option (Multiple choice questions) : Which among the following has white light?

Determine the torque on a bolt, if you are pulling with a force of 250 N directed perpendicular to a wrench of length 20 cm.

Do gases also excert pressure? Do they also exert pressure on the walls of their containers?

Find the force that produces a pressure of 20 kPa on an area of 0.20 m^2?

The time in seconds taken for 20 oscillations noted down in an simple pendulum experiment are 38.6, 40.0, 41.5, 42.8 and 39.4, the time period of the given simple pendulum is ____ s

If the distance between two successive crests of a wave is 12 cm, then the distance between two successive troughs is ___

Find the amount of heat enegy required to convert 100 g of ice at -10^(@)C into stea at 120^(@)C. (Take S_(ice)=0.5" cal "g^(-1).^(@)C^(-1),S_(W)=1" cal "g^(-1)^(@)C^(-1),S_("Steam")=0.5" cal "g^(-1).^(@)C,L_(f)=80" cal "g^(-1),L_(V)=540" cal "g^(-1))

What will happen if two surfaces in contact are pressed harder?

What is audible sound?

State whether the following statement are true or false : Earthquakes occurs at a time all over the earth.

On a certain scale of temperature, the freezing and boiling points of water are maked as 20 and 180 degress, respectively. What is the temperature of a patient suffering with a high fever of 104^(@)F on that scale?

If the percentage decrease in the length of a simple pendulum is 10%, then find the percentage decrease in its time period

Calculate the pressure in the following cases : (i)On the surface ofa block , if it weighs 60 N and is lying on a side with area 0.3 m x 0.1 m. (ii)On the same 60 N block , if it is lying on a side with area 0.1 m x 0.2 m .

What do you do to make a football move?

To increase the stability of a ship

If the speed of light in air is 3 xx 10^8 m/s, and the refractive index of water is 1.33, find the speed of light in water.

Choose the correct option (Multiple choice questions) : The size of the pupil is controlled by the________.

What is the mass of air in a room measuring 10.0 m x 5.2 m x 2.5 m, if the density of air is 1.3 kg//m^3 ?