Question

1. Why are dish antennas curved?
2. What type of lens is formed by a bubble inside water?
3. It is possible for the two lenses to produce zero power?
4. Why does the sky look blue and clouds look white?
5. Why is yellow light preferred during fog?

Answer 1

Hint : The more the number of radio signals the antenna captures, the better connection we get for our television. Make use the property of a concave mirror.
We know that the air has the least value of refractive index among all the matter. Therefore, the refractive index of bubbles is less than the surrounding water.

Complete Step By Step Answer:

1. A dish antenna collects the available signals (electro-magnetic waves) that fall into the spectrum of radio waves. The more the number of radio signals the antenna captures, the better connection we get for our television. We know that a concave surface reflects light that falls on it and converges at a single point (i.e. its focus). Therefore, the dish antennas are curved and the receiver is placed at the focus of the concave surface to receive the maximum number of waves.
2. The medium inside a bubble is air. We know that the air has the least value of refractive index among all the matter. Therefore, the refractive index of bubbles is less than the surrounding water. As a result, when light enters the bubble from water, the rays bend away from the normal and appear to be diverging. Therefore, we can say that a bubble forms a diverging lens in water.
3. Yes, it is possible for two lenses to produce zero power if one of the lenses is a converging lens and the other is a diverging lens. The converging lens will have a positive power and the diverging lens will have a negative power. Therefore, the combination of the two can have a zero power.
4. Clouds are made up of small water droplets, which have the right size to scatter the light of all the available wavelengths. Since the clouds scatter all the light passing through them, the scatter light still appears white. Whereas, the air molecules present in the sky have particles with size that can scatter only blue light. Therefore, the sky appears to be blue in colour.
5. Fog contains tiny water droplets that can scatter the light passing through it. This makes the traveller difficult to travel in the fog. Therefore, yellow light is preferred in fog as it gets scattered less.

Note :
Note that the concept of light (optics) can be applicable for all other electro-magnetic waves as light is also an electro-magnetic wave.
When the refractive index of a lens is less than that of the surrounding medium then it acts as a diverging lens. Whereas, when the refractive of the lens is greater than that of the surrounding medium then it acts as a converging lens.