The definition of incidence is In geometric optics, the angle of incidence is the angle between a ray incident on a surface and the line perpendicular to the surface at the point of incidence, called the normal.
The relationship between the number of visible spectral lines are identical for atoms .However they have unique wavelengths.
Option B
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Explanation:</u>
A spectrum is a range of frequencies or a range of wavelengths. The photon energy of the emitted photon is equal to the difference between two states. For every atom there are quite many electron transitions and each has a energy difference.
This difference in wavelength causes spectrum .As each element emission spectrum is unique because each atom has different energy and causes uniqueness in the emission spectrum . Hence, due to the difference in energy it emits different wavelengths.
Answer:

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

Intensity of sound is given by

So,

We get

The ratio is 
He has 1 1/30 gallons, or 31/30 gallons, you can find this by setting all the fractions to a common denominator and adding them
Direction. Velocity is a vector that describes both speed and direction, while speed is a scalar that describes only speed regardless of direction.