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ays coming from a long distance parallel to the axis of the concave MIRROR, are reflected towards the focus of the concave mirror along its axis.  The energy of the LIGHT waves (electromagnetic waves) is concentrated at the focus of the mirror.     SIMILARLY, the telecommunication signals are also electromagnetic waves like light rays.  They are incident on the dish antenna from the satellites or other dish antennas placed at long distances.  They are mounted and adjusted so that the axis of the dish antenna points to the satellite or other dish antenna.   Hence, the electromagnetic signals of TV are incident parallel to the axis and get reflected to the focus.  At the focal point of the dish, there is an electronic circuit kept, which absorbs the electromagnetic energy and generates voltage / current.  These voltage / current signals are decoded into image, voice and data signals.

the two vectors.  Let Q < P.Let the angle between the two vectors be Ф.Resultant of      R = P² + Q² + 2 P Q COS Ф  --- (1)   We are given P + Q = 18, => Q = 18 - P.             and,      R = 12.   Angle between R and Q = 90°.We have  .So    P² = R² + Q² - 2 R Q Cos 90°    ----- (2)            =  R² + Q² - 0             = 12² + (18 - P)²              = 144 + 324 + P² - 36 P  =>  36 P =  468   =>  P = 13  =>  Q = 18 - 13 = 5==========================Given R is perpendicular to Q. so angle is 90 deg.Use the equation (1) to find the angle Ф between P & Q, as MAGNITUDES of P, Q and R are known.   The angle between  R and P could be equal to (Ф - 90) deg.

tance between a COMPRESSION and an ADJACENT REFRACTION is WAVE length

e covered in one complete round ie., 40 sec.   = circumference of circle of diameter 200 m   =  π 200  meters.Distance covered in 2 mins 20 sec or 140 sec: =  200 π * 140/40 = 700 π metersIn 140 SECONDS, the athlete makes 3 complete rounds and runs for 20 secs after that.in 40 secs, he runs a complete circle (COVERS 360°).  So in 20 secs, athlete runs half-circle and covers 180°.So at the end of 140 seconds, athlete is at the diametrically opposite end on the circular track.  The displacement = vector joining the initial position to the final position.  It magnitude = diameter = 200 meters.

ravity if the EARTH.

cloudless day-time SKY is blue because molecules in the air scatter blue LIGHT from the SUN more than they scatter RED light

ength can be calculated by passing a small beam of parallel rays from a long distance through the lens, and then OBSERVING the location of the image formed.  The image (REAL and inverted) is formed at the focus.A small shining object may be kept at multiple distances and the image converged on the axis is captured on the screen.  Then using the lens formula, the FOCAL length can be calculated.Same experiment can be repeated, WHETHER the lens is in air or in water.

H2SO4   ---->  Na2SO4 + 2 H2OExplanation:To BALANCE any CHEMICAL equation, we always OBEY the law of conservation of mass.To balance,STEP 1:Starting from first element (i.e. Na in this case ) check if the NUMBER of atoms in reactants and product are same.STEP 2:If you encounter any lack then multiply it by any number so that there are equal number of atoms of that element both side.Mind it that this is a hit and try method , practice more and more only then you can solve these

w of inertia is WORKS as a key point. the bowler runs from a long DISTANCE before he is throwing a ball towards the BATSMAN. such that he is in high motion. since the ball is in the HANDS of him, it is also get the same motion and force as much as the bowler. the bowler stops his running at a point suddenly with a great speed. by the newtons first law, here law of inertia will applicable. although the bowler stops, the ball travels by continuing its motion upto some distance high with the inertia. this is because of the ball is still have its MOMENTUM and inertia. so the ball is able to go to the batsmen because of these inertia although the bowler stops running.

1/v = 1/161/v = 1/16 + 1/251/v = 25+16/4001/v = 41/400v = 400/41 CM = 9.75 cmimage DISTANCE is 9.75 cm

because the white light from the SUN is a mixture of seven colours and during day the molecules of AIR SCATTER BLUE light from the sunlight.. so the SKY looks blue.

e times appear white due to Re-combination of seven BANDS of colors , that is DISPERSED out by white LIGHT at a CERTAIN angle.

is a long narrow, vertical cavity FORMED in EARTH crust in the earth crust into which underground WATER seeps. Here the water column is heated by volcanic heat at where the temperature is above 100C due to the pressure exerted by the water column above. due to the deeper POSITIONS, this water is very HOT than ground water. therefore bubbles arise and the water pushes up. then the eruption will be started. Due to pressure the water rushes out. thus the geyser continues to spray hot water into air.

is an optical illusion where it APPEARS that water has converted on the road at the distant place but when we go there, we cant find any water.This is due to the variable refractive index as medium and total internal reflection.Explanation: 1. Density of airincreases with HEIGHT. refractive index of AIR increases with density and ALSO with height.2. When the light from tall object like tree or from sky passes through a medium, it suffers refraction and takes a curved path because of total internal reflection.3. The refracted light from sky is reflected from the ground for the observer.4. Hence the observer FEELS the water being present on the road which is virtual image of the sky

is a long narrow, vertical cavity formed in earth CRUST in the earth crust into which underground water seeps. Here the water column is heated by VOLCANIC heat at where the temperature is above 100C due to the pressure exerted by the water column above. due to the deeper positions, this water is very hot than ground water. therefore bubbles arise and the water pushes up. then the eruption will be started. Due to pressure the water rushes out. thus the GEYSER CONTINUES to SPRAY hot water into air.

unt of energy an electron GAINS after being accelerated by 1 VOLT of electricity ,is known as 1 electron volt.is it used to MEASURE energy.

) / (t2 - T1) = constantperhaps T1 = TEMPERATURE at time t = t1 sec       T = temperature t time t = t2 sec The ratio is constant  means the rate of change of temperature is a constant.  The temperature of a body is rising at a uniform rate in time.This means that the body is getting cooled or getting heated at a uniform rate.This could PROBABLY mean that the body is being SUPPLIED a constant amount of heat energy in time.  This means energy/time = power is a constant.

= 1000 kg/m3ex. cnovert 21g/cm3 to kg/m3 21 g/cm3 = 21 * 1000               = 21000 kg/m3

n vector r =  x i + y j  in the x y plane.     force vector  F = m a = m dv/dt = d P / d t    momentum vector  P = m V            P = 2 COS t  i + 2 Sin t  j           F = - 2 sin t  i + 2 Cos t  jAngle of vector P with x AXIS:  Tan Ф1 = 2 Sin t / (2 Cos t) = Tan tAngle of vector F with x axis :  Tan Ф2 = 2 Cos t / (- 2 sin t) = - Cot t          = - tan (π/2 - t) = tan [π - (π/2 - t) ] = tan (π/2 + t)   or    tan (3π/2 - t)Angle between P and F = Ф2 - Ф1Tan (Ф₂ - Ф₁) = - [tan t + Cot t] / [ 1 - tan t  * Cot t ]                     = infinitySo angle  Ф₂ - Ф₁ = π/2The momentum and force vectors are perpendicular to each other.This is the case of UNIFORM circular motion. F is the centripetal force.

rgy spent are used to do work. Ultimately some PART of the energy are wasted due to friction as sound, heat etc. and go to the SURROUNDING. Some part are stored in the bodies on which work is done as its internal energy(KE or PE).Yes, there is transfer of energy from one FORM to another or one body to another while work is being done. For EXAMPLE, when you are pushing a box on the floor, you apply force. Your energy(work is done by your muscles) is converted into kinetic energy of box and heat and sound energy due to friction.No, we can't do work without transfer of energy. For work to be done, there MUST be transfer of energy.

y of SOUND at temperature T°C is given bytemperature at NTP = 0°CLet at temperature T°C, the VELOCITY BECOME 4 timesV = 331.3*4 = 1325.2 m/sSo at 4096.06°C, velocity of sound will be 4 times that of velocity of AIR at NTP.

y of SOUND is GIVEN by

ines, DUE to FRICTION, wear n tear happens. this leads to FORMATION of heat UTILIZING (a part of mechanical energy is converted to heat) which leads to decrease in efficiency of the machine. to PREVENT this, oiling is required.

s DISTANCE travelled in unit time whereas velocity is DISPLACEMENT of a body in unit time.Speed is a scalar quantity whereas velocity is a VECTOR quantity. Speed has magnitude but no direction. Velocity has both magnitude and direction.Speed is always positive. Velocity can be EITHER positive or NEGATIVE.

of FREQUENCY is HERTZ .

box = 500gvolume of box = 450 cm³density = mass / volume⇒ d = 500/450 g/cm³⇒ d = 10/9 g/cm³⇒ d = 1.11 g/cm³relative DENSITY of a SUBSTANCE = density of substance / density of WATERDENSITY of box = 1.11 g/cm³density of WATER = 1 g/cm³relative density of box = 1.11 / 1 = 1.11(note that it has no unit)If density of a substance is less than density of water, it will float on water and its weight in water will be 0. But density of box is higher than density of water. SINCE density of box is higher than density of water, it will submerge in water and it will have some weight in water.weight of box in water =(density of box - density of water)×volume of box×g⇒ weight in water = [(10/9) -1]×450×g                           = [(10-9)/9]×450×g                           = (1/9) ×450×g                           = 50 gSo correct option is (c).

placement is 0 because he STARTS and ENDS at the same point.perimeter of a PARK (circle) = 2πr                                       = 2×22/7×7                                       = 44mone ROUND = 44m7 rounds = 44×7 = 308m

e he travelled = 24+7 = 31mdisplacement is the shortest distancewhen we draw DIAGRAM we get a TRIANGLE(RIGHT angled) and the hypotenuse will be the displacement. so, by pythagoras theoremso hyp² = 24² + 7²   hyp = √576+49   hyp = √625   hyp = 25so the displacement = 25M

is not discoveed by SCIENTIST CORRECTY

of force, right? torque?here it isopening and closing of doors.(ROTATING about the axle)for a FAN, the motor applies torque to compensate for friction.a wheel in a car rotates around its axle.sliding down of a body from incline, normal force SHIFTS its position to apply a torque to compensate for the torque by friction so as to GIVE rotational equilibrium.and then you have the toy named 'top' that rotates about a fixed axis.

equations of MOTION:  s = ut + 1/2 a t^2let Ф be the angle of the inclined plane with the horizontal.Acceleration ALONG the inclined plane = g sin ФLet initial velocity at t = 0 SEC, be u = 0 m/s.     distance travelled up to n-1 sec:  D(n-1) = 1/2 g SinФ * (n-1)²   distance travelled up to  n sec. :  D(n) = 1/2 * g Sin Ф * n²   Distance travelled upto n+1 sec:  D(n+1) = 1/2 * g Sin Ф * (n+1)² Sn = Distance travelled from t = n -1 sec. to  n sec. = 1/2 g Sin Ф * [n² - (n-1)²]       = 1/2 g Sin Ф * (2N - 1)Sn+1  = distance travelled from t = n sec to n+1 sec = 1/2 g Sin Ф * (2n +1)RATIO :  Sn / Sn+1  =  (2n -1) / (2n +1)  = 1 - 1 / (n +1/2)

ken by an OBJECT to COMPLETE one oscillation is called TIME PERIOD.

cation is 1/3.since it is positive, IMAGE produced is virtual.since it is less than 1, image is diminished.A virtual diminished image is formed in case of convex mirror only.So the mirror is convex.(Note: concave mirror ALSO PRODUCES virtual image but it is ALWAYS enlarged)

hatvolume of vessel = Vinitial pressure = Ptemperature is CONSTANT = Tstroke VOLUME of pump = VWHEN 1st "v" volume is taken out, then the pressure decreases in the vessel.let it becomes P₁. Now, the volume of gas (V-v) at pressure P occupies the whole volume of vessel (V) at pressure P₁. SoP(V-v) = P₁VP₁ = P[(V-v)/V]When 2nd "v" volume is taken out, then the pressure decreases in the vessel.let it becomes P₂. Now, the volume of gas (V-v) at pressure P₁ occupies the whole volume of vessel (V) at pressure P₂. SoP₁(V-v) = P₂VP₂ = P₁ [(V-v) / V]P₂ = [P (V-v) / V] [(V-v) / V]P₂ = P [(V-v) / V]²When 3rd "v" volume is taken out, then the pressure decreases in the vessel.let it becomes P₃. Now, the volume of gas (V-v) at pressure P₂ occupies the whole volume of vessel (V) at pressure P₃. SoP₂(V-v) = P₃VP₃ = P₂ [(V-v) / V]P₃ = P [(V-v) / V]² [(V-v) / V]P₃ = P [(V-v) / V]³So final pressure is P₃ = P [(V-v) / V]³Similarly, if we remove n TIMES volume v, then pressure will be

gram.Weight supported by each of 2 left side legs = F1Weight supported by each of 2 right side legs = F2Balance forces in vertical direction:    2 F1 + 2 F2 = 75 + 170 + 160 lb = 405 lb           =>      F1 + F2 = 202.5 lbbalance MOMENTS about point A:      2 * 170 + 3 * 160 - 6 * 2 F2 = 0   =>  F2 = 205/3  lb              =>  F1 = 202.5 lb - 205/3  lb

of RELATIVITY is PROPOSED by ALBERT einstein.it means the mass can be CONVERTED into energy and energy can be converted into mass....also,E=mc^2

a SONIC waves - TRANSVERSE waves.c) motor boat produced waves on water surface - transverse waves. water molecules OSCILLATE up and down.b) the waves will be COMBINATION of both transverse and LONGITUDINAL waves.a) combination of transverse and longitudinal.        the kink will oscillate sideways and the spring will also compress and decompress too.

rect OPTION is (C)[STATIC,sliding,ROLLING]

a noble metal. It does not react with many kinds of chemicals readily.  HOWEVER, it does react with chlorine and some other acids slowly.  It does dissolve in Nitric acid and Hydrochloric acid MIXTURE called aqua regia.  It GETS slowly oxidized over years.  If COPPER or silver is mixed in Gold ornaments, then they do react with acidic chemicals and gases slowly.Gold also collects some dirt and impurities over its surfaces.  In the cleaning processes, possibly  ammonia, aqua regia or some solvent is used to dissolve all impurities collected on the surface.  So a little part of gold also gets dissolved.  If Gold consists of copper also, then some copper also gets dissolved.So during the purification or shining or polishing act, some metal of the ornaments does gets removed.  So its weight DECREASES.

n as friend:- We NEED friction to walk on the floor- the WHEELS of vehicles need friction to roll on the roads- friction is needed while climbing a treeFriction as foe:- friction between parts of MACHINES decreases their EFFICIENCY- it produces a lot of noise and WASTES energy- The life of machines is degraded.

are   GOOD  CONDUCTORS of HEAT and   ELECTRICITY .

s' is the ANSWER