The frequency : a) 7.5 x 10¹⁴ /s
<h3>Further explanation</h3>
Radiation energy is absorbed by photons
The energy in one photon can be formulated as

Where
h = Planck's constant (6,626.10⁻³⁴ Js)
f = Frequency of electromagnetic waves (/s or Hz)
f = c / λ
c = speed of light
= 3.10⁸ m/s
λ = wavelength
The wavelength(λ) of purple light is 400 x 10⁻⁹ m, so the frequency :

Answer:
0.68g/ml
Explanation:
The density of an object is its mass per unit volume. It is calculated using the formula
Density = mass / volume
Mass of stopper weighed = 4.8g
The volume of stopper can be got by subtracting the (volume of water) from the (volume of water+stopper) i.e.
= 39.2ml - 32.1ml
= 7.1ml
Volume of stopper = 7.1ml
Density of stopper= 4.8/7.1
Density= 0.676056
Therefore, the density of the stopper is 0.68g/ml
The features that are shared by the rocks include the melting and cooling of rocks.
<h3>What is a rock? </h3>
It should be noted that a rock simply means a relatively hard naturally occurring mineral material.
Crystals most often form in igneous and metamorphic rocks. The processes that these rocks share that likely promote the formation of crystals is the melting and cooling of rocks.
Learn more about rocks on:
brainly.com/question/398139
The atomic mass unit is presently based on assigning an exact integral mass (in amu) to an isotope of carbon.
<h3>What is the atomic mass?</h3>
The atomic mass is a measurement used in physics and chemistry to denote the average atomic mass of a given element which is measured in the atomic mass unit or amu.
In conclusion, the atomic mass unit is presently based on assigning an exact integral mass (in amu) to an isotope of carbon.
Learn more about the atomic mass here:
brainly.com/question/3187640
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