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6601.

On which effect of electricity does fuse work?

Answer»

SOLUTION :HEATING EFFECT of CURRENT.
Discussion
6602.

What is the accleration of the block and trolly system as the fig., if the coefficient of kinetic friction between the trolly and the surface is 0.04 ? Also Calculate friction in the string. Take g=10"m/s"^2, mass of the string is negligible.

Answer»

Solution :Free body diagram of the block
30-T=3a ........(i)

Free body diagram of the trolley

Where `f_(k)=mu_(k) N=0.04 xx 20 xx 10=8N`
SOLVING (i) & (ii), `a=0.96 m//s^(2) and T=27.2N`
Discussion
6603.

No image is formed on the blind spot of human eye because,

Answer»

CONES are ABSENT
RODS are absent
rods and cones are absent
optic NERVE is absent

Solution :rods and cones are absent
Discussion
6604.

Name the parts of the eye which help in this phenomena and state how they help.

Answer»

Solution :The human eye has the ability to adjust its FOCAL length according to the distance of object, which is known as power of accomodation. While viewing DISTANT objects, CILIARY muscles of the eye relax which makes the eye les thinner. This increases the focal length of the eye lens so that a clear image of the object is formed on the retina. While viewing nearby objects, ciliary muscles CONTRACT which increases the curvature of the eye lens. This decreses the focal length of the eye lens so that a clear image of the object is formed on the retina.
Discussion
6605.

List two observation on the basis of which it may be concluded that the given slide shown binary fission in Amoeba.

Answer»

Solution :(i) Constriction APPEARS and the nucleus elongates and become thinner in the middle.
(II) The nucleus elongates more and more and ultimately divides in TWO followed by the division of cytoplasm.
These observation give a conclusion that the given SLIDE shows binary fission in Amoeba.
Discussion
6606.

Assertion (A) : Carbon has a strong tendency to either lose or gain electrons to attain noble gas configuration. Reason (R) : Carbon has four electrons in its outermost shell and has the tendency to share electrons with carbon or other elements.

Answer»

Both (A) and (R) are TRUE and (R) is correct EXPLANATION of the ASSERTION
Both (A) and (R) are true but (R) is not the correct explanation of the assertion.
(A) is true but (R) is FALSE
(A) is false but (R) is true.

Solution :Both (A) and (R) are true but (R) is not the correct explanation of the assertion.
Discussion
6607.

Staement -1. The apparent position of the star is slightly higher than its actual position. Statement-2 . Density of air increases with lowering height above the surface of the earth. Give reason for Statement 1 with the help of Statement 2.

Answer»

Solution :1. As the density of air increase with lowering HEIGHT above the SURFACE of the earth, the refractive index also increases.
2. Star light coming towardsus travels from rarer medium to denser medium and constantly bends TOWARDS the NORMAL.
This makes the star appear to be higher in the sky as compared to its actual position.
Discussion
6608.

What is lens formula ? Give its sign conventions and assumptions.

Answer»

Solution :If u is the distance of object and v, the distance of image from optical centre of the lens, then focal LENGTH f is related to u and b by
`1/f=1/v-1/u`
which is called lens formula. The formula is equally applicable to CONVEX, concave or any other type of lens (e.g., concavo-convex, plano-convex, convexo-concave, plano-concave etc.).
Sign COnventions. 1. The object is always placed to the left of the lens.
2. All distances parallel to principal AXIS are MEASURED from optical centre of the lens.
3. All distance measured to the right of optical centre (along x-axis) are taken as positive while those measured to the left of the optical centre (along x-axis) are taken as negative.
4. Distances measured perpendicular to and above the principal axis (along y-axis) are taken as positive.
5. Distances measured perpendicular to and below the principal axis (y.-axis) are taken as negative.
Assumptions. 1. Object is taken on principal axis.
2. The lens is thin.
Discussion
6609.

Explain giving reason why the sky appears blue to an observer from the surface of the earth? What will the colour of the sky be for an astronaut staying in the international space station orbiting the earth? Justify your answer giving reason.

Answer»

Solution :Sunlight reaches the Earth.s ATMOSPHERE and is scattered in all DIRECTIONS by the gases and PARTICLES in the air. BLUE light is scattered more than the other colours because it has the SHORTEST wavelength. This is why the sky appears blue to an observer from the surface of the Earth.
Discussion
6610.

The sky appears dark to the passengers flying at very high altitudes. Why ?

Answer»

SOLUTION :There is no SCATTERING of LIGHT due to lack of atmosphere.
Discussion
6611.

(a) Why are fuses fitted in the fuse box of a domestic electricity supply ? (b) What device could be used in place of the fuses ?

Answer»


SOLUTION :(B) MCB
Discussion
6612.

State Newton's Universal Law of Gravitation. Explain how the value of the Gravitational constant can be determined by Cavendish method.

Answer»

Solution :Newton's law of GRAVITATION : Every BODY in the universe attracts every other body with a force which is directly proprotinal to the product of their masses and inversely proportional to the square of the distance between them.
`F prop m_1M-2" and " F prop (1)/(d^2)" or "F prop (m_1m_2)/(d^2)` or `F=(Gm_1m_2)/(d^2)`
This is always a force of attraction and acts along the line joining the two bodies.
Canvendish experiment to find gravitationl constant 'G' : Cavedish experiment consists of a long METALIC rod AB to which two small lead spheres of mass 'm' are attached.
This rod is suspended from a rigid support with the help of a thin WIRE. Two heavy spheres of mass M are brought near tothese small spheres in opposite direction. Then gravitational force will act between the spheres.

Force between the spheres, `F=(GMm)/(d^2)`
Two equal and opposite forces acting at the ends of the rod AB will develop force couple and the rod will ROTATE through an angle `'theta'`.
Torque on the rod `FxxL=(GM*m)/(d^2)L to (1)`
Restoring force couple= `tautheta to(2)`
Where `tau` =Restoring couple per unit twist
`:. tau theta=(GMm)/(d^2)L" or " G=(tau*theta d^2)/(MmL)`
By measuring `theta` we can calculate 'G' value when other parameters are known.
Practical value of G is `6.67xx10^(-11) Nm^2`/`kg^2`.
Discussion
6613.

Explain different ways to induce a current in a coil .

Answer»

SOLUTION :(1) A current can be induced ina coil by movinga magnettowards or away from it or by movingthe coiltowards or awayfrom the MAGNET.
(2)A currentcan be induced in a coil by changing the CURRENTIN the coil placed near it .
(3) A currentbe induced in a coil by movinga coil properly in a non-unifrom magneticfield or bychanging a magnetic field aroundsteady coil bysomemeans .
(4) A currentcan beinducedin coil byrotatingit properlyin magneticfield or by rotatinga magnet properlyplaced near the coil .
Discussion
6614.

Vulnerable species: Lion ::"______________":: Red panda

Answer»

Solution :Rare species.
Lion is an EXAMPLE of vulnerable species, WHEREAS RED PANDA is an example of rare species.
Discussion
6615.

Which types of telescopes are orbiting around the earth ? Why is it necessary to put them in space?

Answer»

Solution :An optical telescope called the Hubble telescope , an X- ray telescope named Chandra, an X-ray telescope and detector in the artificial satellite Astrosat are orbiting the earth.
(i) Some of the visible light rays coming from HEAVENLY bodies are absorbed by atmosphere. HENCE, the intensity of the light reaching the surface decreases.
(ii) Change in atmospheric pressure and TEMPERATURE causes the light rays to change their path slightly and disturb the position of the image.
(iii) Optical telescopes cannot be used during day- time because of sunlight . During night , City lights and cloudy weathercause difficulties in observing the heavenly bosies.
(iv) X=ray telescopes are desigened to observe X-ray emitting objects from SPACE. Earth 's atmosphere blocks almost all the X-rays coming from space.
To OVERCOME all these difficulties , it is necessary to put these telesopes in space.
Discussion
6616.

Consider the following reasons for the reddish appearance of the sun at the sunrise or the sunset :(A) Light from the sun near the horizon passes through thinner layers of air.(B) Light from the sun covers larger distance of the earth's atmosphere before reaching our eyes.(C) Near the horizon, most of the blue light and shorter wavelengths are scattered away by the particles.(D) Light from the sun near the horizon passes through thicker layers of air.The correct reasons are

Answer»

(A) and (C) only.
(B), (C) and (D).
(A) and (B) only.
(C) and (D) only.

SOLUTION :(B), (C) and (D).
Discussion
6617.

The outer edge of a curved road is generally raised over the inner edge. Why ?

Answer»

SOLUTION :In addition to the FRICTIONAL force, a component of reaction force ALSO PROVIDES CENTRIPETAL force.
Discussion
6618.

In the electrolysis of water What would happen if dil. H_(2)SO_(4)is not added to water ?

Answer»

Solution :PURE WATER is not a good CONDUCTOR of electrolysis. Therefore DIL. `H_(2)SO_(4)` has to be ADDED for electrolysis to start.
Discussion
6619.

Name any three forms of energy which could be harnessed from the Oceans.

Answer»

SOLUTION :(i) TIDAL ENERGY(ii)sea WAVES energy, and
(iii) OCEAN thermal energy.
Discussion
6620.

The explosion of hydrogen bomb is based on the principle of

Answer»

UNCONTROLLED FISSION REACTION
fusion reaction
controlled fission reaction
none of the above

Solution :uncontrolled fission reaction
Discussion
6621.

In the given circuit diagram, calculate : (a) the value of current through each resistor (b) the total current in the circuit (c) the total effective resistance of the circuit.

Answer»

Solution :(A) `I_(1) =(V)/(R_(1))=(12)/(5) = 2.4 A `
`I_(2)=(V)/(R_(2))= (12)/(10)= 1.2 A `
`I_(3) = (V)/(R_(3))=(12)/(30) =0.4 A `
(b) Total current `I=I_(1)+I_(2)+I_(3)`
`=2.4 A+1.2 A +0.4A`
(c ) Total effective resistance `(1)/(R) =(1)/(R_(1))+(1)/(R_(2))+(1)/(R_(3))`
`=(1)/(5)+(1)/(10)+(1)/(30)`
`=(10)/(30)=(1)/(3) OMEGA`
`R = 3 Omega`
Discussion
6622.

Explain how the heating effect of electric current is utilized in an electric bulb (called incandescent lamp) to produce light.

Answer»

Solution :When an electric current passes through a very thin, high-resistance TUNGSTEN filament ofan electric bulb, the fflament becomes white-hot and emits light.
Here, tungsten metal is used for making the filament of an electric bulb because it has a very high melting point (of `3380^@C`). Due to its very high melting point, the tungsten filament can be kept white-hot without melting away.

The other properties of tungsten which make it SUitable for making filament of an electric bulb are its high flexibility and law rate of evaporation at high temperature.
If air is PRESENT in an electric bulb, then theextremely hot tungsten filament would burn upquickly in the presence of oxygen in air.
So, the electric bulb is filled With a CHEMICALLY nonreactive (INACTIVE) gas like argon or nitrogen (or a mixture of both). The gases like argan and nitrogen do not react with the hot tungsten filament and HENCE prolong the life of the filament of the electric bulb.
In electric bulb, most of the electric energy for(power) consumed by the filament appears as heat (due to which the bulb becomes hot), only a small amount of electric energy (power) isconverted into light.
So, filament type electric bulbs are notpower- efficient. On the other hand, tube lights are much more power efficient because they haveno filaments.
Discussion
6623.

Name the mirror that can give an erect and enlarged image of an object.

Answer»

Solution :When an OBJECT is PLACED between the pole and the principal FOCUS of a concave mirror, the image formed is virtual, erect and ENLARGED.
Discussion
6624.

According to the survey published by "______________", 30% of the animal species have become extinct from 1975-2005.

Answer»

IPCC
UNEP
WWF
IUCN

Answer :C
Discussion
6625.

Parallel unequal forces are acting in ……………………… directions.

Answer»

SOLUTION :OPPOSITE
Discussion
6626.

Which part of the eye works like a photographic plate of a camera ?

Answer»

RETINA
Pupil
Iris
Cornea

Solution :Retina
Discussion
6627.

Which of the following statements is false ?

Answer»

The direction of magnetic field lines is from north POLETO south pole
If magneticfieldlines are CLOSER, there is strong magnetic field
The magneticfield lines FORM closed loops.
The magnetic field lines can CROSS ONE another.

Answer :D
Discussion
6628.

The resistivity of chromium is____________.

Answer»

`1.62 xx 10^(-8)`
`6.84 xx10^(-18)`
`12.9 xx 10^(-8)`
`2 xx 10^(-7)`

Answer :C
Discussion
6629.

(a) How does the electronic configuration of atom relates to its position in the modern pèriodic table. (b) Would you place the two isotopes of chlorine C-35 and CI -37, in different slots because of their different atomic masses are in the same slot because their chenical properties are the same. Justify your answer.

Answer»

Solution :In the periodic table elements are PLACED acrording to their atomic number. If an element has only one shell in its electronic configuration it is placed in the FIRST period, if the element has two shells then it is placed in the sccond period and so on. Vertical column in the periodic tuble in group all the elements have same number or valence clectron.
No. C1 35 and CI - 37 will be placed in same sior. The moderan periodie table is based on atomic numbers not atomic MASS since, both CI-35 and Cl - 37 have same atomic numbers HENCE they are placed in same slot.
Discussion
6630.

A wave of length 0.60 cm is produced in air and travels with a velocity of 340ms^(-1). Will it be audible to human ear?

Answer»

Solution :WAVELENGTH, `lamda=0.6xx10^(-2)m`
Velocity of sound, `V=340ms^(-1)`
Frequency, `n=(v)/(lamda)`
`=(340)/(0.6xx10^(-2))=566.66xx10^(2)`
`n=567xx10^(2)Hz`
Discussion
6631.

A body of mass M starts sliding down an Inclined plane where critical angle is lt ACB=30^(@) as shown in figure, the coefficient of friction will be

Answer»

`(MG)/(SQRT3)`
`sqrt3Mg`
`sqrt3`
NONE of these

Solution :`mu=tan 60^(@)=sqrt3`
Discussion
6632.

The intensity of magnetic field at any point produced by a current flowing through a wire, is dependent on the ............

Answer»

SOLUTION :CURRENT
Discussion
6633.

What are the advantages of nuclear energy?

Answer»

SOLUTION :Nuclear ENERGY is PREFERRED to fossil energy, hydroenergy, THERMAL energy etc. for the FOLLOWING reasons.
1. A smaller space is required to get nuclear energy as compared to harness hydro energy, thermal energy, etc.
2. It produced much more energy than other conventional sources.
3. It costs less.
4. It causes less pollution than possil energy.
Discussion
6634.

What happens to the image distance in the eye when we increase the distance of an object from the eye ?

Answer»

Solution :The IMAGE DISTANCE remains same, equal to the distance of the retina from the EYE lens.
The change in object distance is compensated by the change in the FOCAL length of the eye lens due to the action of ciliary muscles so that a clear image is formed on the retina.
Discussion
6635.

Ratio of change in dimension to the original dimension per degree kelvin change in temperature is ..............

Answer»

COEFFICIENT of linear EXPANSION
coefficient of cubical expansion
coefficient of THERMAL expansion
coefficient of areal expansion.

Solution :Coefficient of linear expansion `("Change in dimension")/("Original dimension" XX DELTAT)`
Discussion
6636.

An electric iron of resistance 20 ohm takes a current of 5 A. Calculate the heat developed in 30 s.

Answer»

Solution :Here, current I = 5 A,
resistance R = 20 `Omega`, time t = 30 s
Now,
HEAT produced `H = I^2Rt`
`= (5)^2 xx 20 xx 30`
` = 25 xx 20 xx 30`
`= 15000 J`
` =15 kJ`
Discussion
6637.

Mention three advantages and three disadvantage of producing hydroelectricity by building dams on rivers. (b) given reason for the following (i) A solar cooker box is covered with a glass plate (ii) Asolar cooker box is painted black from inside

Answer»

Solution :(B) (i) Glass plate increases the inside temperature of the solar COOKER DUE to the GREEN house effect of infrared rays of sun
(ii) Black colour absorbs the HEAT energy quickly.
Discussion
6638.

The far point of a myopic person is 150cm in front of eye, calculate the focal length and the power of lens to enable see distant object clearly.

Answer»

Solution :Far point V = 150 CM
USING LENS formula `= 1/F = 1/v = 1/u` `/f = (-1/150) - (-1/oo) `
` 1/f = -1/500`
`f = -150 , " power " = 100/150 = 2/3 =- 0.66D`
Discussion
6639.

(i) Explain Soddy and Fajan Radioactive displacement law. (ii) Calculate the ph of 0.05MH_2SO_4.

Answer»

Solution :Alpha decay :
(a) Unstable parent nucleus emits an alpha particle to form stable daughter nucleus.
(b) `""_(92)U^(238)RARR ""_(90)Th^(234)+""_2He^4(alpha-"decay")`
(C) Mass number decreases by 4.
(d) Atomic number decreases by 2.
Beta decay :
(a) Unstable parent nucleus emits a beta particle to form stable daughter nucleus .
(b) `""_15P^(32)rarr_(16)S^(32)+_(-1)e^(theta)(beta-"decay")`
(c) Mass number - no change
(d) Atomic number increased by 1.
Gamma decay:
(a) The atomic number and the mass number remain same .
(b) Te energy level of the nuceleus change.
`[H^+]` = Normality = MOLARITY `xx` basicity
`=0.05xx2 = 0.1`
`=10^(-1)= 1 xx10^(-1)`
`pH = -log _(10) [H^+]`
`pH = -log _(10) 1 xx 10^(-1)`
`pH = - log _(10)1 - log _(10) 10^(-1)`
`pH = 0-(-1log_(10)10)=1`
Discussion
6640.

(a) What is meant by saponification? Give an explanation. Draw the strueture of the followlng compound and identify functional group present in them. i) Butanoic acid(ii) Bromopropane.

Answer»

Solution :It is the reaction that formS soap when an ESTER reacts with water in the presence of base a salt of carboxylic acid and an alcohol are produced. Sucha reaction is called saponification.
For example: When ETHYL ethanote is HEATED with a solution of sodium hydroxide sodium cthanote and ethanol are produced.
`CH_(3)COOC_(2)H_(5)+NaOHrarrCH_(3)COONa+C_(2)H_(5)OH`
Function group is carboxylie acid

(ii) Function group is BROMINE
`H - underset("H")underset(|)overset("H")overset(|)(C)-underset("H")underset(|)overset("Br")overset(|)(C)- underset("H")underset(|)overset("H")overset(|)(C)- underset("H")underset(|)overset("H")overset(|)(C)-H`
Discussion
6641.

(a) Explain the following terms related to spherical lenses : (i) optical center(ii) centre of curvature. (iii) prinicipal axis(iv) aperture (v) principal focus(vi) focal length (b) A converging lens has focal length of 12 cm. Calculate at what distance should the object be placed from the lens so that it forms an image at 48 cm on the other side of the lens.

Answer»

Solution :(a) (i) Optical center. It is a point within the lens that lies on the principal axis through which a ray of light passes undeflected.
(ii) Centre of curvature. The centre of curvature of the surface of a lens is the centre of the sphere of which it forms a part. A lens has TWO centres of curvature because it has two surfaces.
(iii) Principal axis. It is a line throughthe centres of curvature of the lens.
(iv) Aperture. The diameter of the circular boundary of the lens is CALLED the aperture of the lens.
(v) Principal focus. A beam of light parallel to the principal axis wither converges to a point or appears to diverge from a point on the principal axis after refractin through the lens, is called the principal focus. All lenses have two principal focuses.
(vi) Focal length. The DISTANCE between the optical centre and the principal focus of the lens is called its focal length.
(b) A converging lens is a convex lens.
`f= +12 cm ``u = ?``v= +48 cm( + ve` as it is formed on other side of the object )
According to lens formula
`(1)/(f) = (1)/(v) - (1)/(u) IMPLIES (1)/(12)=(1)/(48) - (1)/(u)`
`(1)/(u) = (1)/(48)-(1)/(12)=(1-4)/(48)=(-3)/(48)= (1)/(16)"":. u = -16`
`:. ` The object should be placed 16 cm away from the lens.
Discussion
6642.

The endarch condition is the characteristic feature of

Answer»

ROOT
stem
LEAVES
FLOWERS

ANSWER :B
Discussion
6643.

Themagnetic field is ………in theregion where the magnetic field lines are very closeto eachother.

Answer»


ANSWER :1
Discussion
6644.

Two identical particles moves towards each other with velocities 2V and V respectively. The velocity of centre of mass is

Answer»

V
`V//3`
`V//2`
ZERO

SOLUTION :`V_(cm) = (m_(1)v_(1) + m_(2)v_(2))/(m_(1) + m_(2)) =(m(2V) + m(-v))/(2m) = V/2`
Discussion
6645.

What is meant by power of a lens ? Write its SI unit. A student uses a lens of focal length 40 cm and another of -20 cm. Write the nature and power of each lens.

Answer»

SOLUTION :The power (P) of a lens is defined as the reciprocal of its focal length (f) expressed in metre.
Thus, `P = (1)/(f ("in m"))`
SI unit of power is dioptre (D), where 1 D = 1 `m^(-1)`
The focal length of lens used by ONE student `f_(1) = + 40 CM = + 0.4`m
`therefore` The lens is a convex lens and the power of lens `P_(1) = (1)/(f_(1)) = (1)/(0.4) = + 2.5` D
Again the focal length of lens used by another student, `f_(2) = - 20 cm = - 0.2 m`
`therefore` The lens is a concave lens and the power of lens `P_(2) = (1)/(f_(2)) = (1)/((-0.2)) = - 5.0` D
Discussion
6646.

Whichof th followingis bestinsulator ?

Answer»

Carbon
paper
EBONITE
Graphite

SOLUTION :Ebonite
Discussion
6647.

Triploblastic

Answer»

SOLUTION :A condition in which there are three GERM LAYERS, viz, ECTODERM, mesoderm and endoderm is CALLED triploblastic.
Discussion
6648.

List three factors whichcan cause overloading of domesticeletriccircuits .

Answer»

Solution :There FACTORS which can cause overloadingare :
(1) Direct contact of the livewireand neutralwire .
(2) Accidental high risein the supplyvoltage .
(3) Connectingtoo mayappliances to a singlesocketand USINGTHEM SIMULTANEOUSLY.
Discussion
6649.

State the application of DNA finger printing technique.

Answer»

Solution :The drugs which act on the brain and alter the behaviour, consciousness, power of thinking and perception, are called Psychotropic drugs. They are also called MOOD altering drugs.
(b) (i) DNA FINGERPRINTING technique is widely used in forensic APPLICATIONS like crime investigation such as identifying the culprit.
(ii) It is also used for paternity testing in case of disputes.
(iii) It also helps in the study of genetic DIVERSITY of population, evolution and speciation.
Discussion
6650.

Keeping the potential difference constant, the resistance of a circuit is doubled. The current will become

Answer»

DOUBLE
Half
One-fourth
Four times

Answer :B
Discussion