A protostar reaches equilibrium when gravity is balanced by the outward force of nuclear fusion.
Answer:
1. Current is usually the flow of <u>electrons</u>.
Explanation:
The flow of charges through a wire or conductor is called electric current.
Answer:
The wavelength in vacuum is equal to 428.8 nm.
Explanation:
Given that,
The wavelength of light, 
The refractive index of glass, n = 1.51
We need to find the wavelength in vacuum. The relation between wavelength and refractive index is given by :

So, the wavelength in vacuum is equal to 428.8 nm.
3. Sand has a low specific heat compared to air
Answer:
Any two forces acting on each other, which are not equal and opposite ( thereby causing motion ) are unbalanced forces.
Explanation:
Expierience