11 & 12 - THE WORKING PRINCIPLES BEHIND ARTIFICIAL SATELLITES; Miscellaneous Facts | RAS RPSC Prelims Preparation - Notes, Study Material & Tests - RPSC RAS (Rajasthan) PDF Download

11. THE WORKING PRINCIPLES BEHIND ARTIFICIAL SATELLITES

A satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.
To place a satellite at a height of 300 km, the launching velocity should at least be about 8.5 km s-1 or 30600 mph. If this high velocity is given to the rocket at the surface of the Earth, the rocket will be burnt due to air friction. Moreover, such high velocities cannot be developed by single rocket. Hence, multistage rockets are used. To be placed in an orbit, a satellite must be raised to the desired height and given the correct speed and direction by the launching rocket At lift off, the rocket, with a manned or unmanned satellite on top, is held down by clamps on the launching pad Now the exhaust gases built “up an upward thrust which exceeds the rocket's weight. The clamps are then removed by remote control and the rocket accelerates upwards. To penetrate the dense lower part of the atmosphere, initially the rocket rises vertically and then tilted by a guidance system. The first stage rocket, which may burn for about 2 minutes producing a speed of 3 km s-1, lifts the vehicle to a height of about 60 km and then separates and falls back to the Earth. The vehicle now goes to its orbital height, say 160 km, where it moves horizontally for a moment. Then the second stage of the rocket fires and increases the speed that is necessary for a circular orbit. By firing small rockets with remote control system, the satellite is separated from the second stage and made to revolve in its orbit.

12. Miscellaneous Facts:

• The distance travelled is given by area under the curve of velocity-time graph.
• The value of G is 6.67 x 10^-11 N-m²/ Kg². Centripetal Force = mv²/r.
• Kinetic Energy = ½ mv². Potential Energy = mph.
• Temperature in Celsius = 5/9 ( T_f  - 32). Bimetal strips are used in thermostat.
• The equatorial radius is greater than polar radius by 21.5 km. Centrifugal force is zero exactly at the poles. Newton’s first law is regarding inertia. Second law states that the rate of change of momentum of a body is directly proportional to the applied force & takes place in the direction of the force.
• Force = mass x acceleration. Momentum = mass x velocity. Impulse = force x time.
• Work = Force x distance in the direction of force. Power = work done/ Time taken.
• Moment of a force = Force x Perpendicular distance of the line of action of force from the axis.
• Escape Velocity: GMm/r² = mv²/ r. Solving we get: v = (GM/r) ^1/2. Moreover the centripetal force is equal to the gravitational force. Therefore, mv²/r = mg. Solving we get v = (rg) ^1/2. g = GM/r². From the equation v = (GM/r) ^½, we see that v is inversely proportional to the square root of r. Thus if a satellite moves from a higher orbit to a lower one, its speed increases. Since the earth rotates form west to east, Satellites are launched in a easterly direction to give them additional push.
• The substances in ascending order of density are aluminium, copper, lead, mercury, gold & platinum.
• Pressure is force/area. The pressure P at a depth h in a liquid of density, is P = h g.
• In a hydraulic press the fundamental is that the ratio of the weight & Area should be the same on both the sides when the opposite plates are at the same level. For e.g. 10 N/ 5 cm² = 80 N/ 40 cm².
• When ice melts in water the level of water remains unchanged as the ice contracts.
• Stokes law for determining viscous force, F is F = 6πηrv where η is the coefficient of viscosity, r is the radius & v is the velocity. After a stage the object acquires critical velocity which is higher for heavier objects.
• Pressure in a fluid decreases with increased velocity of the fluid.
• Surface tension causes the hairs of a paint brush to contract when it is taken out of water. Also sprinkling kerosene on water reduces its surface tension. Capillarity causes water to rise in a glass tube but mercury to drop because of differential cohesion & adhesion.
• Latent heat of fusion is the heat required to convert a solid to liquid state.
• Velocity of a wave V = f, where f is frequency & is wavelength. The number of images formed in case of an inclined mirror = [(360^o – 1)/ Angle] – 1. Hence when angle is 90 three images will be formed.
• Concave/convex mirrors are made by depositing vaporized aluminium on a glass surface. A convex mirror & plane mirror always form virtual image. A concave mirror forms a virtual or real image depending on the position of the object. When the object is at a distance lower than the focal length the image formed is larger & virtual. Hence concave mirrors are used in make-up mirror & by dentists. If an object is held close to a convex lens then the image formed is virtual & vice- versa. In case of a concave or diverging lens all images are virtual.
• Refractive index is the ratio of speed of light in vacuum to speed in that medium.
• The planets do not appear to twinkle due to lesser refraction of the light coming from them due to lower distance. Light can always pass from one medium to an optically denser medium but not vice versa due to total internal reflection.
• Violet light travels at the slowest speed & red the fastest in transparent medium. Rainbow is formed by dispersion & total internal reflection.
• Red + Green = Yellow. Red + Blue = Magenta & Green + Blue = Cyan. Two colours which when mixed give white are known as secondary colours like blue & yellow.
• In eye accommodation is achieved by ciliary muscles. Hypermetropia is treated by converging lens & myopia by diverging lens. Power of a lens = 1/ focal length.
• A compound microscope has two short focal length converging or convex lens. The image seen in a microscope is inverted. An astronomical telescope has an objective of long focal length & an eye lens of short focal length. An astronomical telescope also produces an inverted image. In terrestrial telescope an extra lens is placed in between to produce an erect image of the object.
• In a CD rainbow like colours are produced due to diffraction & reflection & not due to interference.
• Sound waves below 16 Hz are infrasonic & above 20,000 Hz ultrasonic. The presence of water vapour increases the speed of sound. It travels faster on a hot day than cold day. On a warm day the air near the ground is warmer than the air above. This causes bending of sound away from the ground. The opposite happens on a cold day causing the sound to bend towards the earth. Thus on a cold day sounds can be heard over long distances.
• The angle which a suspended bar magnet makes with the horizontal is called the angle of dip of the place. It is zero at equator & 90^o at poles.
• When a glass rod is rubbed with silk, the glass rod loose electrons & becomes positively charged & VV.
• Resistance of a conductor R = L/A where is a constant called resistivity, L is length & A is area. Resistivity of a good conductor increases with temperature whereas for semiconductors it decreases.
• Positive ions collect at cathode & negative at anode.
• Heat produced by current H = I²Rt, where I is current in amperes, R is resistance in ohms & t is time.
• An inverter converts DC into AC. In domestic AC supplies 220 V is the effective value. The peak value of voltage is 311 V. The frequency is 50 Hz. A Fuse is made of tin-lead alloy. A fluorescent tube contains mercury vapours at low pressure. Infra-red signals are used in TV.
• Protons & neutrons are 1836 times heavier than electrons. The heaviest natural atom is that of Uranium. Artificial transmutation has been used to obtain elements beyond uranium. X rays are produced when accelerated electrons strike tungsten sheet. Number of protons is the atomic number & protons + neutrons form the mass number. For short distances nuclear forces are stronger than electrostatic repulsive forces.
• In fission Uranium (235) splits into Barium (56) & Krypton (36) & ejects 3 neutrons. Graphite or Heavy water is used as moderator. Boron or Cadmium is used as controlling rods.
• Bright spots which are actually clusters of stars & gaseous clouds are called Nebulae. Orion Nebula is one of them in the Milky Way. Major constellations are Orion (hunter), Cygnus (swan), Hydra, and Hercules etc. Hydra is the largest with 68 stars visible to naked eye & Centaurs has 94 stars.
• Stars with mass less 1.4 times solar mass (Chandrasekhar Limit) converts into a white dwarf. Bigger than this converts neutron star (pulsar). Still bigger (mass greater than 5 times solar mass) end up as black holes.
• The layers of sun are photosphere (core), chromosphere (surface) & corona (sun’s atmosphere).
• Ganymede, Calisto, & Titan are bigger than planet mercury. Uranus, Neptune & Pluto cannot be seen by naked eye. Ceres is the largest known asteroid.
• Keller’s first law states that each planet moves in an ellipse with the sun at one focus. Second law says that a line drawn from a planet to the sun sweeps out equal area in equal times. The third law states that the ratio of the square of the planets year (T) to the cube of the planet’s mean distance (A) from the sun is same for all the planets.
• An OR gate gives a 1 if either of the input signals is 1. NOT gate generates a signal which is reverse of the original signal.
• TCP (transfer control protocol), URL (universal resource locator), XML (Extensible mark-up language). CGI (common gateway interface).
• One mile = 1.6 km. One nautical mile = 1.85 km. One gallon = 4.5 litres. 1 mm Hg = 133.3 Pascal. One ounce (oz) = 31.1 grams. Parsec = 3.26 light years.
• Bessemer process is for making steel from cast iron.
• Isotones are nuclei having same number of neutrons but different number of protons. Isotopes have same number of protons but different neutrons. Isobars are nuclides with the same mass number.Positron is antiparticle of
• Positron is antiparticle of electron. Tachyons are particle supposed to travel at a super-luminal velocity.
• According to Ohm’s law, V = IR, & power P = VI or P = I²R.
• The earthling pin is longer to ensure that the gadget is earthed first & is thicker so that even by mistake it cannot be inserted in the live hole of the socket.
• The f-number in a photographic camera is the focal length divided by the diameter of aperture.