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3901.

Selwyn is 16 yr old and wears a spectacle having a power of +2 D. Answer the following questions: State two reasons why this defect is caused?

Answer»

Solution :Curvature of the cornea and the EYE LENS decreases so that, the CONVERGING power of the lens becomes less .
Due to the FLATTENING of the eye ball the distance between the lens and retina decreases.
Discussion
3902.

An object , moving with a speed of6.25 m//s , is decelerated at a rate given by : (dv)/(dt) = - 2.5 sqrt (v) where v is the instantaneous speed . The time taken by the object , to come to rest , would be :

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1s
2s
4s
8(s)

Solution :`(dv)/(dt) =-2.5 SQRT(V)`
`int_(6.25)^(0) v^(-1//2)dv = int_(0)^(t) 2.5 dt `
`[(v^(1//2))/(1//2)]_(6.25)^(0)=2.5 [t]_(0)^(t)`
`2[0-sqrt(6.25)]= -2.5 (t-0)`
`2[-2.5]= -2.5t`
`t=2s`
Discussion
3903.

(a) Name two metals which can evolve hydrogen gas by reacting with very dilute nitric acid (b) Explain the formation of MgO by transfer of Electrons.

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Solution :(a) Magnesium and Manganese
(b) Formation LOSES twon ELECTRONS , and forms Magnesium ions to complete its octet.
`Mg rarr Mf^(2+) +2^( e )`
OXYGEN gains that two electrons to becomes `o^(2-)`
`Mg^(2+) +O_(2) rarr MgO`
Discussion
3904.

(i) The given figure shows a domestic electric circuit. Study this circuit carefully. List any two errors in the circuit and justify your answer. (ii) Give one difference between the wires used in the element of an electric heater and in a fuse. (iii) List two advantages of parallel connection over series connection.

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Solution :(i) Two errors are :
(a) Fuse is incorrectly CONNECTED to the neutral wire (N), it must be connected to the live wire (L).
(b) Bulb`B_(2)` is not connected to the neutral wire.
(c) Two SWITCHES `S_(1)and S_(2)`in both `B_(1)` circuit and no switch in bulb `B_(2)` circuit.
(ii) Element of ELECTRIC heater-high melting point
Element of fuse wire - low melting point
(iii) (a) Each appliance has equal POTENTIAL difference.
(b) Each appliance has separate switch to ON/OFF the flow of currentthrough it.
Discussion
3905.

In Fleming.s left- handrule , …….denotes the directionof the magneticforce .

Answer»

thethumb
the FOREFINGER
the MIDDLE FINGER
the palm

Solution :thethumb
Discussion
3906.

The rate of change of displacement with time is

Answer»

SPEED
accerelation
retardation
VELOCITY

Solution :The rate os CHANGE of DISPLACEMENT with time is velocity.
Discussion
3907.

Which type/types of power genetation involve maximum number of steps of energy conversion ? In which power generation is the number minimum?

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SOLUTION :The STEPS of ENERGY conversion are maximum in the thermal power generation. They are MINIMUM in WIND energy generation.
Discussion
3908.

Match the following: {:("(a) Atavism", "(i) A wing of a bat an A a wing of an insect"), ("(b) Atavism", "(ii) Rudimentary tail"), ("(c) Homologous organs", "(iii) Vermiform appendix"), ("(d) Analogous organs", "(iv) a forelimb of cat and a bats wing"):}

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Solution :(a) (II) `""` (B)(iii) `""` (c) (IV) `""` (d) (i)
Discussion
3909.

A binary star systemconsists of two stars A and B which have time periods T_(A)" and "T_(B) radius R_(A)" and "R_(B) and masses m_(A)" and "m_(B) which of the three quantities are same for the stars. Justify.

Answer»

Solution :Angular velocity of BINARY stars are same is `omega_(A) = omega_(B)`.
`(2PI)/(T_A)= (2pi)/(T_B) IMPLIES T_(A)=T_(B)`.
Discussion
3910.

Velocity of sound varies directly as the square root of the

Answer»

SOLUTION :ABSOLUTE TEMPERATURE of the GAS
Discussion
3911.

Statement - 1 : Image formed by concave lens are not formed on screen. Statement-2 : Virutal image is always formed. With the help of Statement 2 expain Sattement 1.

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Solution :1. Image formed BUY concave lens are always virtual IMAGES only.
2. Virtual images are formed not by actual intersection or meeting of rays but rather are formed by extending the rays.
3. Since, the rays do not ACTUALLY MEET, the images are not formed on the screen.
Discussion
3912.

A student wears spectacles with concave lenses for proper vision. When he is not using the spectacles, the image of object is formed :

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in FRONT of the RETINA
on the BLIND spot
behind the retina
on the YELLOW spot

Solution :in front of the retina
Discussion
3913.

Whenelectriccurrentis passedthroughthesolenoid, itsshowsmagneticlinesof force similar toa _______.

Answer»

BAR MAGNET
horseshoemagnet
DISC magnet `
sphericalmagnet

ANSWER :A
Discussion
3914.

It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.(i) What should be the range of the object distance in the above case ?(ii) Will the image be smaller or larger than the object ? Draw a ray diagram to show the formation of image in this case.(iii) Where will the image of this object be, if it placed 24 cm in front of the mirror ?

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Solution :(i) OBJECT must be placed between pole and focus point of CONCAVE mirror i.e., `U lt 12` cm because f = 12 cm.
(ii) The image will be larger than the object. RAY diagram has been drawn here.

(iii) If object is placed at u = 24 cm, then it means that the object is situated at 2f distance from the pole of mirror (i.e., at the centre of curvature of mirror). Obviously its REAL and inverted image is formed there itself. Thus `upsilon = 24` cm.
Discussion
3915.

Define anaerobic degradation.

Answer»

SOLUTION :The DECOMPOSITION which takes PLACE in the absence of oxygen By ANAEROBIC bacteria is CALLED anaerobic degradation.
Discussion
3916.

Onecansensecoloursonly inbright light. Can you explain why?

Answer»

Solution :i. The retina in our eyes is made of different cells viz., ROD-shaped and cone-shaped.
ii. The rod shaped cells RESPOND to INTENSITY of hght and send the information to BRAIN. While cone shaped cells send information of different colours of light to the brain.
iii. Rod like cells are sensitive to faint light, whereas, the comcal cells do not respond to faint light.
Hence, one can SENSE colours only in bright light.
Discussion
3917.

Ohm's law : resistance :: Joule's law : _______________

Answer»

SOLUTION :HEALING EFFECT (or) HEAT
Discussion
3918.

Draw the symbol of a fuse.

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SOLUTION :
Discussion
3919.

Out of the two wires X and Y shown below, which one has greater resistance ? Justify your answer.

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SOLUTION :Wire Y because `R prop L`
RESISTANCE of a conductor is directly proportional to the length of the conductor, whose area of CROSS- SECTION is the same.
Discussion
3920.

If 220 V potential difference is applied across an electric bulb, a current of 0.45 A flow in the bulb. What must be the power of the bulb?

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99 W
70 W
45 W
22 W

Discussion
3921.

Galileo suggested, that an external force is requiredto keep a body in uniform motion.

Answer»


SOLUTION :CORRECT STATEMENT : Aristotel EXPLAINED .
Discussion
3922.

A student uses spectacles of focal length - 2.5 m. Name the defect of vision he is suffering from.

Answer»

SOLUTION :The student is SUFFERING with myopia (or SHORT sightedness) defect of vision.
Discussion
3923.

Explain the structure of Disaster Management Authority.

Answer»

Solution :i. In India, the Disaster Management Act was passed in 2005.
ii. The authority established by the government from national to village level, to CONTROL and coordinate disaster management is known as the Disaster Management Authority.
iii. The structure of the disaster management authority is a shown in the FOLLOWING chart:

IV. At the district lievel, the District Collector is responsible for disaster management and implementation of rehabilitation schemes. He is responsible for designing schemes for each district with respect to each type of disaster and sanctioning those from the state level authorities.
v. As per the Disaster Management Act, 2005, the National Disaster Response FROCE (NDRF) has been established for responding appropriately to different TYPES of disasters.
Discussion
3924.

What would happen to the direction of rotation of a motor, ifi] the current was reversed ?ii] both current and magnetic field were reversed simultaneously ?

Answer»

Solution :i] Direction of rotation WOULD be reversed.
II] Direction ofrotation would remain UNCHANGED.
Discussion
3925.

Define the least distance of distinct vision. What is its value ?

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Solution :The minimum DISTANCE from the eye at which OBJECTS can be seen CLEARLY and distinctly without any strain is called the least distance of distinct vision. For a NORMAL eye. Its value is 25 CM.
Discussion
3926.

Assertion: Artificial radioactivity is an controlled process. Reason: It is a spontaneous process - natural radioactivity,

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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
If Assertion is true, but the reason is FALSE.
If Assertion is false, but the reason is true.

Solution :Explanation: Artificial radioactivity is an CONTROLLED PROCESS. It is an induced process and man-made radioactivity,
Discussion
3927.

For production of radio-isotopes , we use _____________ reactions.

Answer»

research
power
production
absorber

Answer :A
Discussion
3928.

What is meant by nuclear waste ?State the main hazard of this waste on living beings. How is this waste disposed off?

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SOLUTION :(a) The discarded material from the NUCLEAR industry is callednuclear waste, such as REMAINS of the radioactive productsof nuclear reactions.
(b) The waste materials possess radioactive rays which emit particles that can damage man, ANIMALS, and plant tissues.
(C) Nuclear wastes have to be buried deep inside the earth.
Discussion
3929.

How will you classify hydrocabons?

Answer»

Solution :Hydrocarbons are classified into three classes such as Alkanes, ALKENES and Alkynes.
(a) Alkenes: These are hydrocarbons, which contain only single bonds. They are represented by the general formula `C_n H_(2n+2)` (where = 1,2,3) Ex: Methane `(CH_4)`
(b) Alkenes: The hydrocarbons, which contain one or more C = C bonds are called alkenes. These are unsaturated compounds. They are represented by the general formula `C_nH_2n`. Ex: Ethylene `(C_2H_4)`
(c) Alkynes: The hydrocarbons containing carbon to carbon triple BOND are called alkynes. They have the general formula `C_nH_(2n-2)`. Ex: Acetylene `(C_2H_2)`
(ii)• Lower hydrocarbons are gases at room temperature E.g. methane, ethane are gases.
• Alkanes are least reactive when alkynes are most reactive due to presence triple bond.
• Alkanes are saturated whereas alkenes and alkynes are unsaturated.
• They are insoluble in water.
Discussion
3930.

The power of lens depends on the focal length of the lens

Answer»


ANSWER :1
Discussion
3931.

Water cycle, Nitrogen cycle, Oxygen cycle, Carbon cycle

Answer»

SOLUTION :Water CYCLE
Water cycle is not a gaseous cycle, whereas REST are gaseous CYCLES.
Discussion
3932.

Draw the ray diagram showing the recombination of the spectrum of white light

Answer»

SOLUTION :
Discussion
3933.

Assertion : Magnification power of microscopes can be decreeased by increasing the focal length of the lens used.Reason : Due to constructional limitations , the focal length of lens cannot be decreased beyond certain unit.

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If both assertion and REASON are true and reason is the CORRECT explanation of assertion.
If both assertion and reason are true but reason is not the correct explanation of assertion.
Assertion is true but reason is FALSE.
Assertion is false but reason is true.

Solution :Assertion is false but reason is true.
Discussion
3934.

Use the data in Table 2 to answer the following: Which is a better conductor, iron or mercury?

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Solution :The electrical resistivity of iron is `10.0 XX 10^(-8) Omegam` whereas that of MERCURY is `94.0 xx 10^(-8)Omegam`. As the resistivity of iron is less than that of mercury, iron (Fe) is a better conductor than mercury (Hg).
Discussion
3935.

Where does the signal in your cellphone come from ? Where from does it come to mobile towers ? Where does the signal to your TV set come from ? You many have seen photographs showing the position of monsoon clouds over the country, in the newspaper. How are these images obtained ?

Answer»

SOLUTION :1.The signal in the cell phone comes from MOBILE towers.Signal comes to mobile towers from satellites.
3.The signal to our TV set comes from satellites through dish antenna.
4. Weather satellites take photographs of the SKY above the EARTH's surface frequently
These images can be received from the satellites.
Discussion
3936.

An object is placed at a distance of 15 cm from a concave mirror and its real image is formed at 30 cm in front of that mirror. The focal length of the mirror is

Answer»

`+ 20` CM
`-20` cm
`-10` cm
`+10` cm

SOLUTION :Here u = - 15 cm and v = - 30 cm, hence
`(1)/(f) = (1)/(v) + (1)/(u) = (1)/((-15)) + (1)/((-30)) = (-2-1)/(30) = - (1)/(10) rArr f = - 10` cm
Discussion
3937.

Heat system based on circulation of steam are more efficient in warning a building than those based on circulation of hot water why ?

Answer»

SOLUTION :Because STEAM at `100^@C`has more heat than WATER at `100^@C`.
Discussion
3938.

A truck driver loads some oil drums into a truck by lifting them directly. Each drum has a mass of 80 kg and the platform of the truck is at a height of 0.8 m above thground. (a) What force is needed to lift a drum into the truck ? (b) How much energy is used up in lifting a drum? (c) After the truck is loaded, the driver drives off. List the major energy changes that take place in moving the truck. (d) The driver stops the truck at the factory gate. What happens to the kinetic energy of the truck ? Take g=10 m s^(-2)

Answer»

Solution :Given ,m=80 kg,h=0.8 m ,g=10 m`s^(-2)`
(a)Force needed to lift a drum
Force of gravity on drum (b)ENERGY used up in lifting a drum
Gravitational potential energy mgh M
`80xx10xx0.8=640J`
(c )In MOVING the TRUCK ,the chemical energy of the fuel (diesel) changs into mechanical (kinetic) energy .
(d)On stopping the truck ,the kinetic energy og the truck changes into the heat and sound ENERGIES.
Discussion
3939.

Doctor advised to use 2D lens. What is the focal length of it ?

Answer»

<P>

Solution :GIVEN power of lens P=2D
We know, `P=(100)/(F("in cm")) implies2 =(100)/(f) impliesf=(100)/(2) = 50 cm`
`therefore ` Focal length of lens (f)=50 cm .
Discussion
3940.

What expandson reducingitstemperaturebelow______ ""^(@)C

Answer»

0
4
12
5

Answer :B
Discussion
3941.

The pulley & strings shown in figure are smooth and of negligible mass. For the system to remain in equilibrium, the angle theta should be

Answer»

`0^(@)`
`30^(@)`
`45^(@)`
`60^(@)`

Solution :For EQUILIBRIUM of MASS m, T=mg ..........(1)
For equilibrium of mass `sqrt2m`
`2T cos theta =sqrt2mg .........(2)`
SOLVE (1) & (2)
`cos theta=1/sqrt2, theta=45^(@)`.
Discussion
3942.

Name, state and explain with an example the rule used to determine the direction of force experienced by a current carrying conductor placed in a uniform magnetic field.

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Solution :Fleming.s Left Hand Rule : The direction of force which ACTS on the current carrying conductor placed in a magnetic field is given by Fleming.s left hand rule. It states that if the forefinger, thumb and middle FINGER of ieft hand are stretched mutually perpendicular and the forefinger point ALONG the direction of external magnetic field, middle finger indicates the direction of current, then thumb POINTS along the direction of force acting on the conductor.
Exampie : When an electron ENTERS a magnetic field at right angles, the direction of force on electron is perpendicular to the direction of magnetic field and current according to this rule.
Discussion
3943.

Is it possible to place an artificial satellite in an orbit so that it is always visible over New Delhi?

Answer»

Solution :No, A SATELLITE will be always visible only if it REVOLVES in the EQUATORIAL plane, but New Delhi does not lie in the region of EQUITORIAL plane.
Discussion
3944.

________ define as the property which determines whether a body is an equilibriumor not with its surroundings.

Answer»

SOLUTION :TEMPERATURE
Discussion
3945.

(a) (i) State the principle of moments as applied to the lever shown in Figure. And (ii) calculate its mechanical advantage if AB=2*0m and FA=20cm. (b) Calculate the effort needed to lift and load.

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Solution :(a) (i) By the principle of moments.
Load`xx`FA=Effort`xx`FB
(ii) Given: `AB=2*0m,FA=20cm=0*2M`.
FB=AB-FA=`2*0-0*2=1*8m`.
`THEREFORE`Mehcanical ADVANTAGE=`("effort arm FB")/("load arm FA")`
`=(1*8m)/(0*2m)=9`
(b) Given: load=18 kgf, M.A.=9
Since `M.A.=("load")/("effort")`
`therefore`Effort=`("load")/("M.A.)=(18)/(9)=2kgf`.
Discussion
3946.

Fertilization in plants is called double fertilization.

Answer»

Solution :(1) After pollination the pollen grains drop on the sticky stigma of the flower. (2) They germinate here producing two malegametes and a long pollen TUBE. (3) The MALE GAMETES travel through the pollen tube till they reach the embryo sac. Here the male gametes are released by bursting the pollen tube. (4) One male gamete unites with the egg cell to form zygote while the second male gamete unites with two polar nuclei forming ENDOSPERM. (5) In this way becausetwo nuclei participatein the fertilization process, thereforeit is called doublefertilization.
Discussion
3947.

State the effect on the strength of magnetic field produced at a point near a straight conductor if the electric current flowing through it increases.

Answer»

SOLUTION :The STRENGTH of the MAGNETIC FIELD INCREASES
Discussion
3948.

A truck eighine 1000 kg changes its speed from 36 km h^(-1) to 72 km h^(-1) in 2 minutes. Calculate (i) the work done by the engine, and in its power (g 10 m s^(-2))

Answer»

Solution :`1.5 XX 10^(5)J`(II) `1-25 xx 10^(3)W`
Discussion
3949.

What are analogous organs?

Answer»

Solution :Analogous organs are those organs which look similar and perform similar FUNCTION but have DIFFERENT origin and DEVELOPMENT pattern. (eg). Function of the wings of a bat, wings of a bird and wings of an INSECT are similar but their basic structure are different.
Discussion
3950.

_________ is used to select the magnitude of the current through the circuit.

Answer»

SOLUTION :VARIABLE RESISTOR (or) RHEOSTAT
Discussion