Answer:
0.78 m
Explanation:
The relationship between wavelength and frequency of a wave is given by

where
v is the speed of the wave
f is the frequency
is the wavelength
For the sound wave in this problem, we have
is the frequency
v = 344 m/s is the speed of sound in air
Substituting into the equation and re-arranging it, we find the wavelength:

Answer:
Revolving nosepiece
Explanation:
The revolving nosepiece is one of the parts of a microscope, used for holding the objective lenses. They can be turned to put a particular objective lens in place to be used in order to vary magnification.
Answer:
Material's density
Explanation:
Seismic waves travel at different rates of speed based on a material's density. Hopefully, you understand that the Earth has three main layers: the crust, mantle, and core. Earthquake waves move faster through solids.
If one of two interacting charges is doubled, the force between the charges will double.
Explanation:
The force between two charges is given by Coulomb's law

K=constant= 9 x 10⁹ N m²/C²
q1= charge on first particle
q2= charge on second particle
r= distance between the two charges
Now if the first charge is doubled,
we get 
F'= 2 F
Thus the force gets doubled.