Answer:D. λfilm/4
Explanation: Destructive interference is a type of wave interference which means the coming together or over-lapping of two opposing waves creating No effect or the Cancellation of the wave impact. An example of destructive wave is when Noise cancel the effect of sound from a head phone.
The film thickness will need to be increased by λfilm/4 for it to be able to give a destructive interference.
Answer:

Explanation:
c = Speed of wave
= Density of medium
A = Area
= Frequency

Intensity of sound is given by

So,

We get

The ratio is 
Answer:
Explanation:
The volume of a sphere is:
V = 4/3 * π * a^3
The volume charge density would then be:
p = Q/V
p = 3*Q/(4 * π * a^3)
If the charge density depends on the radius:
p = f(r) = k * r
I integrate the charge density in spherical coordinates. The charge density integrated in the whole volume is equal to total charge.





Since p = k*r
Q = p*π^2*r^3 / 2
Then:
p(r) = 2*Q / (π^2*r^3)
Answer:
you should write about a book you read
Explanation:
because maybe you got really good things in it
or here is an example