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1301.

Find the work done if a particle moves from position r_(1)=(3hati+2hatj-6hatk) to a positon vecr_(2)=(14hati+13hatj-9hatk) under the effect of force vecF=(4hati+hatj+3hatk)N.

Answer»

Solution :`VECR=vecr_(2)-vecr_(1)=11hati+11hatj-3hatk`
`vecF=(4hati+hatj3hatk)N`
`:.W=vecF.vecr=46J`
Discussion
1302.

Namethephysical qulitieswhich are indicated by the directionof the thumb and forefinger in Fleming.s right - handrule .

Answer»

SOLUTION :The thumbdenotesdirection of MOTION of the conductor and the forefingerindicates the direction of the magnetic FIELD .
Discussion
1303.

When soap is added to hard water, it reacts with the salts to form a scum. Why does this scum form ?

Answer»

Solution :This forms due to the FORMATION of calcium and magnesium SALTS of fatty acid which is FORMED when calcium and magnesium ions of hard WATER REACT with soap.
Discussion
1304.

(a) What is biomass ? Give three examples of biomass. (b) Name the biomass which is still widely used as a source of heat energy in many households of our country.

Answer»


ANSWER :(B) WOOD
Discussion
1305.

An alpha-particle, (which is a positively charged particlel enters, a uniform magnetic field at right angles to it as shown below. Stating the relevant principle explain in which direction will this alpha -particle move ?

Answer»

SOLUTION :The alpha PARTICLE will move in a CIRCULAR path. This is because a centripetal FORCE ACTS on the particle due to the movement of particle in the magnetic field.
Discussion
1306.

A spherical mirror and a thin spherical lens have each of a focal length of -15 cm. The mirror and the lens are likely to be

Answer»

both CONCAVE
both CONVEX
the MIRROR is concave and the LENS is convex.
the mirror of the convex, but the lens is concave.

Answer :A
Discussion
1307.

A chargedparticlemovingin a unifrom magneticexperiences a forceofmaximum magnitudewhen direction of motion of charged particleis .

Answer»

parallel to thedirection of magneticfield
at rightangleto the DIRECTIONOF MAGNETIC FIELD
antiparallel to thedirection of magnetic field
inclined at `45^(@)` to thedirectionof magnetic field .

Solution :A CHARGED particleexperiences maximum forcewhen it is
Discussion
1308.

Microbial enzymes are used instead of chemical catalysts inchemical industry.

Answer»

Solution :(1) Microbial enzymes are active at low temperature, pH and pressure.
(2) Due to this property, the energy is saved. The costlier erosion-proof instruments NEED out not be used.
(3) In enzymatic reactions, the unnecessary byproducts are not formed as the reactions are highly specific.
(4) The EXPENSES on purification of the PRODUCT are MINIMIZED as no unnecessary products are formed.
(5) The ELIMINATION and decomposition of waste material is avoided and enzymes can be reused again. Hence, microbial enzymes are said to be eco-friendly.
Discussion
1309.

................ is used to remove the heat produced in the reactor core, to produce steam.

Answer»

SOLUTION : COOLANT
Discussion
1310.

Distinguish between the physical properties of metals and nonmetals with respect to the point : Lustre

Answer»

Solution :Lustre: Metals usually have a HIGH lustre (CALLED METALLIC justre). They can be polished to give a highly reflective surface. With the exceptions of GOLD and COPPER, metals usually have silvery grey colour. Nonmetals lack lustre, exceptions : grphite and iodine. Some nonmetals are colourless and others possess a variety of colours.
Discussion
1311.

Absolute refractive index of a transparent cannot be less than _____________.

Answer»


SOLUTION :N/A
Discussion
1312.

While performing an experiment to determine the equivalent resistance of two resistors connected in parallel, a student observes the pointer of voltmeter at position X when the key is 'off' and the same pointer at position Y when the key is 'on'. The correct voltmeter reading is :

Answer»

0.2 V
2 V
2.2 V
1.8 V

Solution :NA
Discussion
1313.

At what distance from a concave lens of focal length 20 cm, a 6 cm tall object be placed so as to obtain its image at 15 cm from the lens? Also calculate the size of the image formed. Draw a ray diagram to justify your answer for the above situation and label it.

Answer»

Solution :`f=-20CM,h_(1)=6cm,v=-15cm, u=?`
LENS formula `1/f=1/v-1/u`
`impliesu=(VF)/(f-v)`
`(-15cmxx-20cm)/(-20cm-(-15cm))`
`=-60CM`
object at 60 cm from the lens
`h_(2)=v/uxxh_(1)`
`=(-15cm)/(-60cm)xx6cm`
`=+1.5cm` diiminished erect
Discussion
1314.

Draw schematic diagram of a circuit consuting of a battery of five 2V cells, a 5 ohm, a 10 ohm and a 15 ohm resistor and a plug key, all connected in series. Calculate the electric current passing through the above circuit when the key is dosed.

Answer»

Solution :The requued circuit DIAGRAM is :

APPLIED potential difference
`V=5xx2=10 V `
Total RESISTANCE
R = 5 +10+15=30 `Omega`
Current `I= (V)/(R) = (10)/(30) = 0.33A `
Discussion
1315.

What are the two disadvantages of burning fossil fuels ?

Answer»

SOLUTION :DISADVANTAGES are air pollution and ACID rain which AFFECTS soil and water.
Discussion
1316.

Match the following. {:("1. Linear momentum",-,"(a) Mass and acceleration"),("2. Force",-,"(b) Change in momentum"),("3. Moment of force",-,"(c ) "GM//R^(2)),("4. Impulse",-,"(d) Mass and velocity"),("5. Acceleration due to gravity",-,"(e) Force and perpendicular distance"):}

Answer»

Solution :1. (d) MASS and velocity
2. (a) Mass and acceleration
3. (e) Force and PERPENDICULAR distance
4. (B) Change in momentum
5. (c ) `GM//R^(2)`
Discussion
1317.

What is the othernameof Right- handthumb rule ?

Answer»

SOLUTION :Maxwell.scorkscrew RULE
Discussion
1318.

Gobar gas is :

Answer»

Foul smelling GAS
SWEET smelling gas
having high CALORIFIC VALUE
useless

Answer :C
Discussion
1319.

Define elastic and inelastic collision. A lighter body collides with a much more massive body at rest. Prove that the direction of lighter body is reversed and massive body remains at rest.

Answer»
Discussion
1320.

Objects beyond and above a holy fire appear to be shaking. Give scientific reasons.

Answer»

Solution :YES.
(i) The air NEAR the holi flame is hotter than the air above, hence it is a rarer medium than the air above.
(ii) Because of this change of medium the refractive index keeps on changing as we go higher and higher above the flame and so the REFRACTION of light also changes.
(iii) This gives a shaking EFFECT to OBJECTS beyond and above holy fire.
Discussion
1321.

Twinkling of stars is due to atmospheric.

Answer»

dispersion of LIGHT by water droplets
REFRACTION of light by different layers of varying refraction indices
scattering of light by dust particles
internal reflection of light by clouds.

Solution :Twinkling of stars is DUE to refraction of light by different layers of atmosphere having varying refractive indices.
Discussion
1322.

Jupiter has a mass 318 times that of earth, and its radius is 11.2 times the earth's radius Estimate the escape velocity of a body from Jupiter's surface, given that the escape velocity from the earth's surface 11.2 kms^(-1).

Answer»

Solution :Escape VELOCITY from the earth's surface is
`v_e =sqrt((2GM)/(R )) = 11.2 kms^(-1)`
Escape velocity from JUPITER's surface will be
`v_e' = sqrt((2GM')/(R'))`
But `M' = 318 M, R'= 11.2 R`
`v_e' = sqrt((2G(318M))/(11.2))= sqrt((2GM)/(R )xx(318)/(11.2))`
`v_e'xx sqrt((318)/(11.2))= 11.2xx sqrt((318)/(11.2))= 59.7 kms^(-1)`.
Discussion
1323.

The equivalent resistance between points X and Y in the circuit shown in the following figure is ………………. .

Answer»

SOLUTION :`5 OMEGA`
Discussion
1324.

A coil of isulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil (ii) Withdrawn from inside the coil (iii) held stationary inside of coil?

Answer»

Solution :(i) When a bar magnet is PUSHED into the coil, a momentary DEFLECTION is observed in the GALVANOMETER. This deflection indicates that a momentary CURRENT is producedin the coil.
(ii) When a bar magnet is HELD stationary inside the coil, there is no deflection in the galvanometer. It indicates that no current is produced in the coil.
(iii) When a bar magnet is withdrawn from the coil, the deflection of galvanometer is in opposite direction. It indicates that a current of an opposite direction is produced.
Discussion
1325.

List two main causes of the pollution of water of the river Ganga . State how pollution and contamination of river water prove harmful for the health of the people of neighbouring areas.

Answer»

Solution :CAUSES for pollution of water of river Ganga ,
(i)Dumping of untreated SEWAGE
(ii)INDUSTRIAL wastes
Effects :
(a) Growth of disease - causing microorganisms in the river water.
(b)The river water becomes more ACIDIC which makes the soil acidic and affects the productivity of CROPS.
Discussion
1326.

Name the gland which release thyroxin.

Answer»

SOLUTION :THYROIDGLAND
Discussion
1327.

Explain the use of concave lenses in the following: Torch

Answer»

Solution :(d) Torch - Concave lens is USED to spread widely the light PRODUCED by a small BULB inside a torch.
Discussion
1328.

Two blocks of masses 8 kg and 2 kg respectively, lie on a smooth horizontal surface in constant with one other. They are pushed by a horizontally applied force of 15 N. Calculate the force exterted on the 2 kg mass.

Answer»

Solution :Given: `m_(1)=8KG, m_(2)=2kg, F=15N`
`F=m_("total"), F=(m_(1)+m_(2))a=(8+2)a=10a`
`15=10 a RARR a=(15)/(10)=(3)/(2)MS^(-2)`
`therefore"Force exerted by MASS of 8kg"`
`F_(1)=m_(1)=a=8xx(3)/(2)=12N`
Discussion
1329.

Ability to change one's own behaviour according ot changing social conditions is an important characteristic of social health.

Answer»


ANSWER :TRUE.
Discussion
1330.

In an electric circuit three resistors R_1,R_2 and R_3 are connected in series such that R_2=R_3. IF V_1,V_2 and V_3 are the voltage across R_1,R_2 and R_3 respectively , then

Answer»

`V_1=V_2`
`V_2=V_3`
`V_1=V_3`
`V_1=V_2=V_3`

SOLUTION :Since `R_2=R_3` and in a series CIRCUIT same current J FLOWS through the ENTIRE circuit here `V_2=V_3`
Discussion
1331.

Which of the following persons can donate their eyes after death ? A person suffering from (i) Hepatitis B (ii) myopia (iii) leukaemia (iv) asthma.

Answer»

Solution :A person suffering from (ii) and (IV) can donate their eyes SINCE they are not suffering from CONTAGIOUS disease and their cornes is WORKING PROPERLY.
Discussion
1332.

Two resistances when connected in parallel give resultant value of 2Omega, when connected in series the value becomes 9Omega. Calculate the value of each resistance.

Answer»

Solution :LET `R_(1)andR_(2)` be the two resistances.
When they are in PARALLEL, resultant resistance `R_(p)` is given by
`1/R_(p)=1/R_(1)+1/R_(2)`
`R_(p)=(R_(1)R_(2))/((R_(1)+R_(2)))`
`2=(R_(1)R_(2))/((R_(1)+R_(2)))`
`2[R_(1)+R_(2)]=R_(1)R_(2)`
When they are in series effective resistance
`R_(s)=R_(1)+R_(2)`
`9=R_(1)+R_(2)rArrR_(2)=9-R_(1)`
`2xx9=R_(1)R_(2)=R_(1)[9-R_(1)]=9R_(1)-R_(1)^(2)`.
`18=9R_(1)-R_(1)^(2)`
`R_(1)^(2)-9R_(1)+18=0`
Solving by using quadratic formula, we get
`R_(1)=((9pmsqrt(81-4xx1xx18))/2)""R_(1)=((9pmsqrt9)/2)=((9pm3)/2)`
`R_(1)` = 3 OHM or 6 ohm
If `R_(1)` = 3 ohm, `R_(2)` = 6 ohm and vice VERSA.
Discussion
1333.

…… is used for preparing the filament of an electric bulb.

Answer»

SOLUTION :TUNGSTEN
Discussion
1334.

Draw a ray diagram in each of the following cases to show the position and nature of image formed when the object is placed: (i) Between pole and focus of a concave mirror. (ii) Between focus and centre of curvature of a concave mirror. (iii) At the centre of curvature of a concave mirror. (iv) Between infinity and pole of a convex mirror.

Answer»

SOLUTION :
Discussion
1335.

If the energy of incident beamand the scattered beam are same, then the scattering of light is called as ______________.

Answer»

INELASTIC
elastic
Raman
Rayleigh

Answer :B
Discussion
1336.

Which of the following is not a unit of electric energy?

Answer»

The WATT-second
The KILOWATT HOUR
The joule
The watt

Solution :The watt
Discussion
1337.

How can you decide the focal length of convex lens to be used ?

Answer»

Solution :Here object distance (u)=-25 cm
Image distance (v) =-d (distance of near point)
Let 'F' be the focal LENGTH of bi-convex LENS.
Using the lens formula `1/f =1/v-1/u`
`implies1/f=1/(-d) -1/((-25)) implies1/f =((d-25))/(25d) IMPLIES f=(25d)/((d-25))` (f in centimetres)
If `d gt 25 cm implies` 'f' becomes positive then we NEED to use biconvex lens to correct hypermetropia.
Discussion
1338.

What kind of mirror-concave, convex or plane would be best suited for use in a solar cooker ? Why ?

Answer»

Solution :Concave MIRROR is best suited SINCE it can focus sun rays from large area to a SPECIFIC area. However PLANE mirror may also be used but in no case convex mirror be used. Convex mirror diverges the rays and hence will not transfer sufficient heat to the cooker.
Discussion
1339.

The force of gravity due to earth on a body is proportional to its mass, then why does a heavy body not fall faster than a lighter body?

Answer»

SOLUTION :`:. F= (GMm)/(R^2), F propto m " but "g=(GM)/(R^2)` and does not depend on 'm' HENCE they bodies fall with same 'g'.
Discussion
1340.

Listany four advantages of water harvesting.

Answer»

Solution :Four advantages of water havesting :
(i)Water collected in ground does not evaporate , but spreads out to recharge wells and providesmoisture for vegetation over a wide area.
(II)The groundwater is also relatively protected from contamination by human and animals waste.
(III)It provides year round supply of drinking water .
(IV)It does not provide breeding grounds for mosquitoes like stagnant water collected in PONDS or artificial lakes.
Discussion
1341.

_______ is used in the treatment of skin diseases.

Answer»

<P>

SOLUTION :RADIO PHOSPHORUS (`P^(32)`)
Discussion
1342.

Assertion :Property of lens, whether the ray is converging or diverging is independent of the surrounding medium. Reason : The converging property of a convex lens does not be same in all media.

Answer»

Both ASSERTION and REASON are TRUE and reason is CORRECT explanation of assertion.
Both assertion and reason are true but reason is not the correct explanation of assertion.
Assertion is false but reason is true
Both assertion and reason are false

Solution :Assertion is false but reason is true
Discussion
1343.

. (i) Calculate the pH of 0.01 M HNO_3 ?

Answer»

Solution :(i)
(ii) `PH = -LOG [H^+]`
`=-log_(10)^(-2)`
`=(-2)(-log_(10)^(10))`
`= 2 XX 1.00`
`pH = 2`.
Discussion
1344.

Incoldregions, thewinterrockscracksdueto anomalousexpansionof water .

Answer»

Solution :(i) Duringwinterseason,in coldcountriesthe temperaturefor atmospherefallswell below `0^(@)C` .
(ii)If wateris presentwithinin thecrevicesof THEROCKS ,then dueto itsanomalousbehavior ,waterbegins to expand below`4^(@)C`
As there is no PLACEIN thecervices fortheexpansionof water,in exertstermedndous pressureon the rockswhichresult in the crumbling of therocks.
(iv) Hence,sometimesrockscrumbleinto PIECE in coldcountriesduringwinter .
Discussion
1345.

Define the unit of current?

Answer»

Solution :SI unit of ELECTRIC current is ampere. Current is said to be 1 ampere (1A), if 1 coulomb CHARGE flows per SECOND ACROSS a cross section of a conductor.
Discussion
1346.

(i) Name the spherical mirror used as: (a) Shaving mirror (b) Rear view mirror in vehicles (c) Reflector in search lights (ii) Write any three differences between a real a virtual image.

Answer»

SOLUTION :(i) a. SHAVING mirror : Concave mirror
b. Rear view mirror: Convex mirror
C. REFLECTION in search lights: Concave mirror
(II) a. Real image can be obtained on screen but virtual image cannot be obtained.
b. Reflected/Refracted rays actually meet where real image is formed while for virtual image they only appear to meet.
Discussion
1347.

Assertion : Colour of the sun is red at surface and sunset. Reason : The light rays from the sun have to travel a larger distance in the atmosphere than at noon.

Answer»

Both ASSERTION and REASON are TRUE and reason is correct explanation of assertion.
Both assertion and reason are true but reason is not the correct explanation of assertion.
Assertion is true but reason is false
Both assertion and reason are false

Solution :Both assertion and reason are true and reason is correct explanation of assertion.
Discussion
1348.

........... .. is arranged on disaster of fire in various schools by the firefighters.

Answer»


ANSWER : MOCK DRILLS
Discussion
1349.

An optically denser medium is that in which speed of light is more than that in air or vaccum.

Answer»


SOLUTION :SPEED of light in any material medium can NEVER be more than the speed of light in vaccum (or AIR).
Discussion
1350.

Lubricants are used between the two parts of a machine. Why ?

Answer»


ANSWER :To REDUCE FRICTION and so to reduce WEAR & tear.
Discussion