Radio waves are a form of electromagnetic radiation, created whenever a charged object (in normal radio transmission, an electron) accelerates with a frequency that lies in the radio frequency (RF) portion of the electromagnetic spectrum. Thus statement 3 is correct. The Doppler’s Effect shows a change in a wave’s frequency received when it is either reflected from a moving object or generated on a moving object. Police radar speed detectors bounce a radio frequency wave off cars and use their internal electronics to determine the speed at which the object is moving by that frequency change. Therefore, statement 4 is also correct.

Convection currents of hot air rising off a surface have a lower density than the air directly above it. The difference in density cause light passing through the air to refract differently, which causes the formation of mirage.

Dust particles are responsible for the diffusion of light in atmosphere.

The velocity of sound in air is determined by the air itself and is not dependent upon the amplitude, frequency, or wavelength of the sound. The velocity of sound c depends on the temperature of air and not on the air pressure. Thus, velocity of sound in air increases with temperature and remains unaffected with increase of pressure. Therefore, statements 1, 2 and 4 are right. Only statement 3 is wrong. The only other factor that has any effect on the speed of sound in air is the amount of humidity in the air. An increase in the amount of humidity in the air increases the speed by a small amount.

The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at 20 °C (68 °F), the speed of sound is 343.2 metres per second (1,126 ft/s). In fresh water, sound travels at about 1497 m/s at 25 °C. The value of 331.3 m/s which represents the 0 °C speed. The speed of sound at 100 °C is 386 m/s. The speed of sound in wood is 3300 – 3600 m/s.

Combination of red and blue colour results into formation of magenta colour. Where as combination of red and green colour results in to formation of yellow colour. Thus on combination of magenta and yellow colour red colour will be highlighted. On the other side combination of blue and green results into formation of cyan colour. Combination of red and blue colour produce magenta colour. Therefore, on combination of cyan and magenta colours blue colour will be more highlighted.

The flute is a musical instrument of the woodwind family. A flute of smaller length produces waves of higher frequency. Sound waves travels through medium rocks in the form of longitudinal as well as transverse waves.

Mach number, a useful quantity in aerodynamics, is the ratio of air speed to the local speed of sound. The speed of sound varies with temperature. Since temperature and sound velocity normally decrease with increasing altitude, sound is refracted upward. Mach number is a function of temperature at altitude. With decrease in sound velocity Mach number increases.

Radio waves are a type of electromagnetic radiation.

Night Vision as referenced here is that technology that provides us with the miracle of vision in total darkness and the improvement of vision in low light environments. Infra-red waves are used in night vision apparatus.

In the above figure, dotted line shows the reflected beam of light from mirror OP₂.

Size of the Sun at dusk is an optical illusion because of atmospheric refraction. Colour of the sun appears yellow due to scattering whereas pure sunlight is white in colour. Twinkling of stars is an optical illusion. Air whirlpools make the stars twinkle.

Formation of rainbow involves all dispersian, refraction and internal reflection.

Thunderstorms result from the rapid upward movement of warm, moist air. They can occur inside warm, moist air masses and at fronts. As the warm, moist air moves upward, it cools, condenses, and forms cumulonimbus clouds that can reach heights of over 20 km (12.45 miles). The thunderstorms are associated with the cumulonimbus clouds. These clouds normally form on warm sunny days but they can also be found on cold front. But this question is asking about the Thunder i.e. the sound produced. The lightning generates between 100 million and 1 billion volts of electricity and can heat the air to around 50K°F. The rapid expansion causes the shock waves. Thunder happens because the lightning would heat the air at huge temperatures and the air expands so fast that it make a loud clap of thunder.

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors–the transformer’s coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer’s core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a voltage in the secondary winding. By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) or voltage to be “stepped up” by making N_s greater than N_p or “stepped down” by making N_s less than N_p. Here N_p represents number of turns in primary winding. N_srepresents the number of turns in secondary winding. As it is clear from principle involved that transformer can be used to step up and step down A.C. voltage only. This device can not be used for D.C. voltage as its working is based on the change of magnetic flux with varying current.

In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component. The wiring for most homes is parallel. In parallel circuit each branch receives equal current. If one branch in the circuit is broken, electric current will still flow in other branches.

Iron = Ferromagnetic
Hydrogen = Diamagnetic
Oxygen = Paramagnetic
Nitrogen = Diamagnetic

A fuse is a type of sacrificial overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows. Short circuit, overload or device failure is often the reason for excessive current. The resistance of the element used in fuse generates heat due to the current flow. It has low melting point so that it melts when a short-circuit or overloading takes place.

A metallic conductor has a large number of free electrons in it. When a potential difference is applied across the ends of a metallic wire, the free electrons begin to drift from a region of low potential to a region of high potential. These electrons collide with the positive ions (the atoms which have lost their electrons). In these collisions, the energy of the electron is transferred to the positive ions and they begin to vibrate more violently. As a result, heat is produced. The greater the number of electrons flowing per second, the greater will be the rate of collisions and so greater is the heat produced.

The electric light bulb uses a glowing wire filament heated by electrical resistance to white to generate light (a process known as thermal radiation). The ‘bulb’ is the glass enclosure which keeps the filament in a vacuum or low-pressure noble gas. Complete evacuation of bulb is not possible. A small quantity of gases left behind which expands on heating by heat through filament. Moreover, the wires supporting the filament sometimes melt due to high heat generated as a result of high resistance of filament. Thus, these factors leads to short life span of ordinary bulb.