Explanation:
Electromagnetic waves are the waves which are created as the result of the electrical waves which are perpendicular to each other and also perpendicular to the direction of propagation.
Electromagnetic spectrum is range of the frequencies and their respective wavelengths of the various type of the electromagnetic radiation.
In order of the increasing frequency and the photon energy and the decreasing wavelength the spectrum are:
radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
The energy of the radio waves photons is the lowest of all the other waves in the electromagnetic spectrum.
Also, 
Where,
h is Plank's constant having value 
Thus, energy is directly proportional to the frequency. The radio waves have the lowest frequency.
Answer:
a). 87.5 mA or
A
b). 1.78 
Explanation:

n the number of free electrons is 28 in text reference and if they don't give q is take as the charge of electron.
a).
A
b).


Answer:
time required is 6.72 years
Explanation:
Given data
mass m = 3.20 ✕ 10^7 kg
height h = 2.00 km = 2 × 10^3 m
power p = 2.96 kW =2.96 × 10^3 J/s
to find out
time period
solution
we know work is mass × gravity force × height
and power is work / time
so we say that power = mass gravity force × height / time
now put all value and find time period
power = mass × gravity force × height / time
2.96 × 10^3 = 3.20 ✕ 10^7 × 9.81× 2 × 10^3 / time
time = 62.784 × 10^10 / 2.96 × 10^3
time = 21.21081081 × 10^7 sec
time = 58.91891892 × 10^3 hours
time = 6.72 years
so time required is 6.72 years