set 2 MCQ Questions & Answers Detailed Explanation

Answer: (c)

Answer: (c)

Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies.

At present solar energy in our country is used for solar water heater.

Solar lights that charge during the day and light up at night are a common sight along walkways.

Answer: (d)

Following are the problems which are faced while transmitting audio signals directly.

1. These signals are relatively of short range.
2. If every body started transmitting these low frequency signals directly, mutual interference will render all of them ineffective.
3. Size of antenna required for their efficient radiation would be larger i.e. about 75 km.

Answer: (a)

Answer: (c)

Answer: (d)

There is a presence of atmosphere at earth’s surface which consists of thick and moving layers of air. The dust particles, particulates, smog, water vapour and smoke are also present in air.

Stars twinkle when we see them from the Earth’s surface because we are viewing them through thick layers of turbulent (moving) air in the Earth’s atmosphere.

As their light travels through the many layers of the Earth’s atmosphere, the light of the star is bent (refracted) many times in random directions (light is bent when it hits a change in density –like a pocket of cold air or hot air). This random refraction results in the star as its twinkling but for a person in spaceship no such refractions are possible as there is vaccum in space.

Thus, star will not twinkle.

Similarly, sky will appear blue to us due to Rayleigh scattering which is again due to presence of atmosphere on earth’s surface. The shorter wavelength light is absorbed by the gas molecules of atmosphere. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Some of this scattered blue light reaches you.

Since, you see , the sky looks blue. Whereas no atmosphere is there in space thus, no absorbing and scattering is possible that’s why for a person in spaceship sky appears black.

Temperature outside the spaceship is higher in comparison to earth’s surface because of being nearer to sun.