one of the property of radio waves is that they have long wavelength. due to their long wavelength , they undergo diffraction around the mountains and thus the waves spread around the mountain. this makes them eligible to be used for long distance communication. they can coded and decoded also . that is why they are used in television and radio system
Answer:
I think it would be the 3rd or 4th one.
Answer:
20 J
Explanation:
Given:
Weight of the book is, 
Height or displacement of the book is, 
The work done on the book to raise it to a height of 2 m on a shelf is against gravity. The gravitational force acting on the book is equal to its weight. Now, in order to raise it, an equal amount of force must be applied in the opposite direction.
So, the force applied by me should be equal to weight of the body and in the upward direction. The displacement is also in the upward direction.
Now, work done by the applied force is equal to the product of force applied and displacement of book in the direction of the applied force.
Therefore, work done is given as:

Therefore, the work done to raise a book to a height 2 m from the floor is 20 J.