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8801.

Relative humidity less than 60% : Dry air ::Relative humidity more than 60% : ______

Answer»

Solution :Humid air
When RELATIVE HUMIDITY is less than 60%, we feel air is DRY. Whereas, when relative humidity is more than 60%, we feel air is humid.
Discussion
8802.

An electric iron contumea energy at a rate of 840W whe.n heating la at the maximum and 360W, when the heating la at the minimum. The voltage at which it is running is 220V. What are the cunent and resistance values in each case ?

Answer»

<P>

SOLUTION :`P_(1) =840 W ` V= 220 V
Current drawn `I_(1) =(P_(1))/(V)`
`=(840)/(220)= (42)/(11) = 3.8 A `
`P_(2) = 360 W V= 220 V`
Current drawn `I_(2) = (P_(2))/(V)= (360)/(220) = 1.6 A `
By OHM .s Law
`V= I_(1) R_(1)`
`R_(1) =(V)/(I_(1)) = (220)/((42)/(11))=(220xx11)/(42)= (1210)/(21)OMEGA = 57.5 Omega`
`V= I_(2) R_(2)`
`R_(2) =(V)/(I_(2) = (220)/((18)/(11))=220xx(11)/(18)=134.4Omega`
Discussion
8803.

A cannonball of mass 500 g is fired with a speed of 15 ms^(-1) . Find : (i) its kinetic energy, and (ii) momentum

Answer»

Solution :(i) 56 25 J. (ii) 7.5 KG m `s^(-1)`
Discussion
8804.

Why and when does a current carrying conductor kept in a magnetic field experience force ? List the factor on which direction of this force depends ?

Answer»

Solution :The DRIFTING of free electrons of a conductor in a definite direction cause the current to flow through it. When such conduct is placed in a uniform MAGNETIC FIELD each drifting electrons of a conductor experience a magnetic FORCE. This force is collectively experience by a conductor as a whole. Hence a current carrying conductor kept in a magnetic field experiences a force. The direction of magnetic force depends on
(i) Direction of current through the conductor and
(ii) Direction of magnetic field,
Discussion
8805.

Kepler's Law

Answer»

<P>

Solution :Kepler's first law: The ORBIT of a planet is an ellipse with the Sun at one of the foci.
The ADJOINING figure shows the elliptical orbit of a planet revolving around the Sun. S denotes the position of the Sun.
Kepler's second law : The line joining the planet and the Sun Sweeps equal areas in equal intervals of time.
Area ASB=area CSD=areaESF.
Kepler's third law :
The square of the period of revolution of a plant around the sun is directly proportional to the cube of the mean DISTANCE of the planets from the Sun.
Thus , if r is the average distance of the planet from the Sun and T is its period of revolution , then,
`T^(2) prop r^(3), ` i.e. `(T^(2))/(r^(3))` =constant =K
For simplicity we shall assume the orbit to be a circle. In the adjoining figure, S denotes the poistion of the Sun, P denotes the position of a planet at a given instant and r denotes the radius of the orbit(`-=` the distance of the planet from the Sun ). Here, the speed of the planet is uniform. It is
`v=("circumference of the circle")/("period of revolution of the planet")=(2pir)/(T)`
If m is the mass of the planet , the centripetal force exerted on the planet by the Sun(`-=` GRAVITATIONAL force), `F=(mv^(2))/(r)`
`therefore F=(m(2pir//T)^(2))/(r)=(4pi^(2)mr^(2))/(T^(2)r) =(4pi^(2)mr)/(T^(2))`
Accordign to Kepler's third law,
`T^(2)=Kr^(3)`
`therefore F=(4^(2)mr)/(Kr^(3))=(4pi^(2)m)/(K)((1)/(r^(2)))`
Thus, `F prop (1)/(r^(2))` as `(4pi^(2)m)/(K)` is constant in a particular case.

Discussion
8806.

Blue colour of sky is due to the phenomenon of scattering. What is meant by scattering?

Answer»


ANSWER :Irregular and PARTIAL reflection of LIGHT is scattering.
Discussion
8807.

Draw the ray diagram showing the image formation by a convex lens, when the object is at principal focus f 1. with the help of the diagram mention the nature of the image formed.

Answer»

SOLUTION :The NATURE of the IMAGE is REAL and INVERTED,
Discussion
8808.

Lets Think. If frog population declines all of a sudden : Number of which consumers will decline and which will increase ?

Answer»

Solution :If the populaion of frog declines, then the NUMBER of primary consumers, LIKE grasshoppers will increase as the frog that feed upon grasshoppers have reduced in number, WHEREAS the number of tertiary consumers like snakes will decrease as the frogs on which they feed have decreased in number.
Discussion
8809.

A person cannot see distinctly the book placed nearer than 60 cm from his eyes. (i) Name the defect of vision the person is suffering from. (ii) List two possible causes of this defect. (iii) Draw a ray diagram to show this vision defect. (iv) How can this defect be corrected ? (v) Draw a ray diagram to show the correction of this defect.

Answer»

SOLUTION :Hypermetropia, , (ii) . Low converging POWER of eye-less, . Eye BALL becomes short (iii) Hypermetropia is CORRECTED by ysing spectacles containing convex lens.
Discussion
8810.

A fuse should be made of a material of low melting point. Give reason

Answer»

Solution :A fuse is used to protect a circuit and the appliances connected in the circuit by STOPPING the flow of an EXCESSIVE ELECTRIC current. For this, a fuse is connected in SERIES in the eircuit.
(2) When the current in the circuit passes through the fuse, ts TEMPERATURE inereases. When the current exceeds the specified value, the fuse must melt to break the eircuit. For this, the material used for a fuse has low melting point
Discussion
8811.

What is the disired minimum total coliform count level in the Ganga ?

Answer»

500 MPN/100 ML
600 MPN/100 mL
1000 MPN/100 mL
1200 MPN/100 mL

ANSWER :A
Discussion
8812.

List the properties of magnetic field lines.

Answer»

Solution :(i) They travel from north pole to south pole OUTSIDE the magnet and south pole to north pole inside the magnet.
(ii) They are CLOSED and continuous CURVES.
(iii) Two magnetic field lines never intersect each other. If the lines intersect, then at the point of INTERSECTION there WOULD be two directions (the needle would point towards two directions) for the same magnetic field, which is not possible.
(iv) The number of field lines per unit area is the measure of the strength of magnetic field, which is maximum at poles. The magnetic field is strong, where the field lines are close together and weak where the lines are far apart.
Discussion
8813.

Magnification power of microscopes can be included by using of lengths ____________.

Answer»

LARGE FOCAL length eye piece
Objective LENS
SHORTER focal length of the eye piece
Large focal length of objective

Answer :A
Discussion
8814.

Show that trajectory of a projected at angle 'theta' with horizontal is parabolic in nature.

Answer»


ANSWER :CORRECT DERIVATION
Discussion
8815.

Distinguish between Phylum Platyhelminthes and Phylum Aschelminthes,

Answer»

SOLUTION :
Discussion
8816.

Themagnitude of theinducedcurrentin electromagnticinductiondepends on ……… .

Answer»

the motionof the coilonly
the MOTION of the magnet only
the relative SPEED of the coiland magnet
the DEFLECTIONOF the pointerin the galvanomter

Solution :the relative speed of the coiland magnet
Discussion
8817.

If Maximum and minimum values of the resultant of two forces acting at a point are 7N and 3N respectively, the smaller force is equal to

Answer»

4N
5N
3N
2N

Solution :F max. =P+Q=7N .......(1)
F min. =P-Q=3N ..........(2)
From (1) & (2)
`P +cancel(Q)=7""P+Q`
`P-cancel(Q)=3""5+Q`
2P=10
P=5N, Q=2N
Discussion
8818.

Image of an object at infinity is formed in front of retina of an eye, as shown in (Fig. 2.24). What is this defect of vision called ?

Answer»

SOLUTION :The DEFECT of VISION is CALLED myopia or short sightedness.
Discussion
8819.

Assertion: In a beta-decay, the neutron number decreases by one. Reason: In beta-decay atomic number increases by one.

Answer»

if both the assertion and the REASON are true and the reason is the CORRECT explanation of the assertion
If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion
Assertion is true, but the reason is false
Assertion is also, but the reason is true

Solution :In B-decay there is no CHANGE in the mass number of the daughter nucleus but the atomic number increases by ONE.
Discussion
8820.

A resistance of 40 ohms and one of 60 ohms are arranged in series across 220 volt supply. Find the heat in joules produced by this combination of resistances in half a minute.

Answer»


ANSWER :14520 J
Discussion
8821.

Whatare two different forms of the body in coelenterate animals ?

Answer»

Solution :The CYLINDRICAL POLYP and the umbrella LIKE modusa are the two different forms of the bodu in coelenterate animals .
Discussion
8822.

__________ has both magnitude and direction .

Answer»

SOLUTION :FORCE ,
Discussion
8823.

Where should an object be placed from a converging lens of focal length 20 cm, so as to obtain a real magnified image.

Answer»

SOLUTION :`f=20cm, U=?, m=2`
`m=c/uimplies2=v/uimpliesv=2U`
`1/f=1/v-1/u`
`implies1/20=1/(2u)-1/u`
`impliesu=-10cm`
`v=-20cm`
Discussion
8824.

State the characteristics of magneticfield lines.

Answer»

Solution :(1) The magneticfieldlines emergyfrom north pole and merge at the southpole outsidethe magnet ,whileinsidethe magnet the directionof fieldlines is FROMITS south poleto itsnorth pole .
Thus , themagnetic fieldlines are closedand continuouscurve.
(2) The magnetic fieldlines are crowded near the polewhere the magnetic fieldis strongarefar APART near the middle of THEMAGNET and farfrom themagnetwhere the magneticfieldis weak .
(3) Themagnetic fieldlines never intersect each otherbecauseif they do so ,there wouldbe two directions ofmagneticfieldat thatpointwhichis absurd.
(4) In case the field lines are parallel and equidistance , theserepresent a UNIFROM magneticfield .
Discussion
8825.

How is induced current in a secondary coil related to current in a primary coil?

Answer»

Solution :When CURRENT in the PRIMARY COIL changes, a current is INDUCED in the secondary coil.
Discussion
8826.

When the electric power is transmitted over a long distance, it is beneficial to have it in ............ current.

Answer»

SOLUTION :ALTERNATING
Discussion
8827.

The part of human eye which carries electric signals to the brain

Answer»

SOLUTION :OPTIC NERVE
Discussion
8828.

While preparing a temporary stained mount of a leaf epidermal peel, how is the extra stain removed?

Answer»

Solution :While PREPARING a temporary stained MOUNT of a leaf epidermal PEEL, extra stain is REMOVED with the help of the FILTER paper. The filter paper absorbs the extra starch.
Discussion
8829.

How is nuclear fission reaction carried out in nuclear power plants?

Answer»

Solution :(1) In nuclear power plants NEUTRONS are bombareded on atom of Uranium-235.
(2) This causes conversion of Uranium- 235into its isotape U-236.
(3) U-236 is very UNSTABLE and thus forms ATOMS of Barium and Krypton by nuclear fission. This forms 3 neutrons and 200 MeV energy.
(4) In a similar way three more Uranium-235 atoms are subjected to nuclear fission which then releases energy.
(5) The neutrons released are again used for further nuclear fission reactions. In this way nuclear fission reactions are carried out in controlled manner in nuclear power plants.
Discussion
8830.

List three factors responsible for the wind. State three limitations in harnessing wind energy.

Answer»

Solution :Three factors :
(i) Uneven HEATING of the earth.s surface.
(ii) Rotation of the earth.
(iii) Local conditions - such as change in pressure.
Three limitations :
(i) Can be used where WIND blows for a GREATER part of the YEAR.
(ii) Wind speed should be higher than `15 km//h`.
(iii) ESTABLISHMENT is expensive and requires large area.
Discussion
8831.

Since naturalgas contains sulphur burning of natural results in less pollution.

Answer»


Answer :False. Since NATURALGAS does not CONTAIN sulphur BURNING of naturl gas results in in less pollution.
Discussion
8832.

Give the common name of the Hirudinaria granulosa.

Answer»

Solution :(a) Hirudinaria GRANULOSA - Indian CATTLE leech
(B)ORYCTOLAGUS cuniculus - RABBIT
Discussion
8833.

What answer may the passenger give to the driver ?

Answer»

Solution :The CAR is in motion with respect to the observer on the ROAD, but at REST with respect to the passenger. Because motion is a COMBINED PROPERTY of the observer and the body which is being observed.
Discussion
8834.

Refractive index of first medium with respect to second medium is represented by "_(1)n_(2).

Answer»


Answer :False. The REFRACTIVE INDEX of the second medium with respect to FIRST medium is given by the RATIO `v_(1)//v_(2)`
Discussion
8835.

State the Motor Rule. If the directions of current in the conductor and the magnetic field are the same, in which way will the conductor move?

Answer»


Answer :A CONDUCTOR, which can move freely and which is kept.in a MAGNETIC FIELD EXPERIENCES a force when current passes through it and it moves.If the direction of current in the conductor and the magnetic field are the same, the conductor will not move.
Discussion
8836.

Whena wireis moved up and downin a magnetic field ,a currentis indcuedin the wire . What is thisphenomenon known as ?

Answer»

SOLUTION :ELECTROMAGNETIC INDUCTION .
Discussion
8837.

Use the data in Table 12.2 to answer the following- (a) Which among iron and mercury is a better conductor ? (b) Which material is the best conductor?

Answer»

SOLUTION :(a) IRON
(B) SILVER.
Discussion
8838.

Define the term electric power. Write an expression for it.

Answer»

<P>

Solution :ELECTRIC power
Electric power is defined as the rate of consumption of energy or simply the rate of doing work.
i.e., power [P] = Work done [W] / Time [T]…..[i]
The work done by current [I] when it flows in a potential [V] for time [t] can be given by
W = VIT....[ii]
`rArr` Power, [P] = VIt/t=VI
`therefore` Electric power or P = VI
Discussion
8839.

Compare the energy produced during fission of a uranium atom with the energy produced due to combustion of a carbon atom from coal.

Answer»

Solution :The FISSION of an atom of uranium produced 10 million times the ENERGY produced by the combustion of an atom of carbon from COAL.
Discussion
8840.

Define: Acceleration due to gravity and derive mathematically.

Answer»

Solution :The GRAVITATIONAL force due to the EARTH on an object results in its acceleration. It is called acceleration due to GRAVITY.
We know
`F=(GMm)/(R^(2))`…………I
`F=mg` ………ii
From I and ii
`mg=(GMm)/(R^(2))`
For Earth `=g=9.77m//s^(2)`
Discussion
8841.

A man of mass 50 kg climbs up a Indder of height 10 m. Calculate : (i) the work done by the man and (ii) the increase in his potential energy (g = 9.8 ms^(2))

Answer»

SOLUTION :(i) 4900 J, (II)4900 J
Discussion
8842.

Glucose is oxidised step by step in the cells during the process of respiration at the body level.

Answer»


ANSWER :FALSE
Discussion
8843.

Explain the statement-'We have got this earth planet on lease from our future generations and not as an ancestral property from our ancestors.'

Answer»

Solution :i. Planet EARTH is not our ancestral PROPERTY and one cannot makeundue claims on it, or inherit it.
ii. Existence of humans completely depends on the existence of nature, thus it is our responsibility .
iiii. Irrational use of the natural resources leads to their depletion.
iv. Natural resources need to be taken care of asa borrowed property,as we have to sustain theseresources for our FUTURE generations.
v. Humans are entrusted with the RESPONSIBLITY of preserving these natural resources for the coming generations and hence wehave gotthis earth planet on a lease from our future generations.
Discussion
8844.

(a) An object is placed at the centre of curvature (c ) of a concave mirror. Draw the ray diagram to depict the position, size and nature of image formed. (b) Find the focal length of a lens of power - 2.0 D. What type of lens is this ?

Answer»

SOLUTION :(a) The ray diagram is

The image will be real, inverted and of the same size as that of OBJECT. It will be formed at C.
(b) POWER of the LENS = -2.0 D
We know power = `1/("FOCAL length in metres")`
`therefore` Focal length in metres = `1/("Power")=1/(-2.0)=-0.5m`.
Since, the sign of the focal length is -ve, therefore it is a convex lens.
Discussion
8845.

Choose the correct option. The magnetic field inside a long straight solenoid carrying current

Answer»

is ZERO.
decreases as we move TOWARDS its ends.
increases as we move towards its ends.
is the same at all points.

SOLUTION :The field lines INSIDE the SOLENOID are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid. Thus, answer (d) is correct.
Discussion
8846.

Which is considered to be the common reference for a parallel circuit ?

Answer»

Current
Resistance
Power
Voltage

Answer :D
Discussion
8847.

Draw the circuit diagram showing the combination of resistors R_1, R_2 and R_3in parallel including ammeter and voltmeter and mark the direction of current.

Answer»

SOLUTION :
Discussion
8848.

A pure tall plant (TT)is crossed with pure dwarf plant (tt),What would be the F_(1) and F_(2) generations?Explain.

Answer»

Solution :In a monohybrid cross, if a pure tall plant (TT) is crossed with pure dwarf plant (tt). All plants were tall (Tt) in `F_1` generation.

`F_1 to` Tt Tt Tt Tt (Tall HETEROZYGOUS)
RATIO : 3: 1
During the selfing of `F_1` generation 3 DIFFERENT types of plants were produced.

Tall Homozygous -TT(Pure )-1
Tall Heterozygous -Tt-2
Dwarf Homozygous -tt- 1
Ratio : 1: 2: 1
Discussion
8849.

What is The right hand thumb rule (also called Maxwell's cork-screw rule)?

Answer»

Solution :Maxwell's cork SCREW rule : If a RIGHT hand screw is rotated to advance in the DIRECTIONOF the current through a CONDUCTOR, the direction of rotation of the screw gives the direction of the magnetic FIELD produced by the current.
Discussion
8850.

A body of mass 5 kg falls from a height of 10 m to 4 m. Calculate : (i) the loss in potential energy of the body, and (ii) the total energy possessed by the body at any instant ? (Take -10 m s^(-2)

Answer»

SOLUTION :(i) 300 J. (II) 500 J
Discussion