Answer:
D. Frequency
Explanation:
The energy of an electromagnetic wave is proportional to frequency, mathematically it is expressed as;
E ∝ f
E = hf
where;
h is Planck's constant = 6.626 x 10⁻³⁴ Js
The equation above can also be expanded to;

where;
c is speed of light = 3 x 10⁸ m/s
λ is the wavelength of the electromagnetic wave
Since the speed of light is constant, we can conclude that the energy of the electromagnetic wave is directly proportional to its frequency and inversely proportional to its wavelength.
Therefore, the correct option for direct proportionality is FREQUENCY
Let's see: frequency of cellular phone waves (GSM phones) is (800-1900 MHz). If we look at the table of the electromagnetic spectrum, we can see that this range is contained within the frequencies of the microwaves, which include waves in the range 300 MHz-300 GHz.
So, summarizing, the correct answer is "microwaves".
Answer:

Explanation:
= Force on one side of the door by first waiter = 257 N
= Force on other side of the door by second waiter
= distance of first force by first waiter from hinge = 0.567 m
= distance of second force by second waiter from hinge = 0.529 m
Since the door does not move. hence the door is in equilibrium
Using equilibrium of torque by force applied by each waiter

Speed = distance/time
Speed = 50/5
Speed = 10m/s
To solve this problem it is necessary to apply the concepts related to the described wavelength through frequency and speed. Mathematically it can be expressed as:

Where,
Wavelength
f = Frequency
v = Velocity
Our values are given as,

Speed of sound
Keep in mind that we do not use the travel speed of the ambulance because we are in front of it. In case it approached or moved away we should use the concepts related to the Doppler effect:
Replacing we have,


Therefore the frequency that you hear if you are standing in from of the ambulance is 0.1214m