# 9.1 Electromagnetic spectrum

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## Electromagnetic spectrum

Electromagnetic radiation allows us to observe the world around us. Some materials and objects emit electromagnetic radiation and some reflect the electromagnetic radiation emitted by other objects (such as the Sun, a light bulb or a fire). When electromagnetic radiation comes from an object (whether the radiation is emitted or reflected by the object) and enters the eye, we see that object. Everything you see around you either emits or reflects electromagnetic radiation or both.

Electromagnetic radiation comes in a wide range of frequencies (or wavelengths) and the frequencies of radiation the human eye is sensitive to is only a very small part of it. The collection of all possible frequencies of electromagnetic radiation is called the electromagnetic spectrum, which (for convenience) is divided into sections (such as radio, microwave, infrared, visible, ultraviolet, X-rays and gamma-rays).

The electromagnetic spectrum is continuous (has no gaps) and infinite. In practice, we can only use electromagnetic radiation with wavelengths between (very roughly) ${10}^{-14}\mathrm{m}$ (very high energy gamma rays) and ${10}^{15}\mathrm{m}$ (very long wavelength radio waves) due to technological limitations in the detectors used to receive electromagnetic radiation and in the devices used to produce or emit electromagnetic radiation.

The various frequencies (or wavelengths) of electromagnetic radiation coming from a particular object or material depends on how the object or material reflects and/or emits electromagnetic radiation.

## Wave nature of em radiation

1. List one source of electromagnetic waves. Hint: consider the spectrum diagram and look at the names we give to different wavelengths.
2. Explain how an EM wave propagates, with the aid of a diagram.
3. What is the speed of light? What symbol is used to refer to the speed of light? Does the speed of light change?
4. Do EM waves need a medium to travel through?

[link] lists the wavelength- and frequency ranges of the divisions of the electromagnetic spectrum.

 Category Range of Wavelengths (nm) Range of Frequencies (Hz) gamma rays $<$ 1 $>3×{10}^{19}$ X-rays 1-10 $3×{10}^{17}$ - $3×{10}^{19}$ ultraviolet light 10-400 $7,5×{10}^{14}$ - $3×{10}^{17}$ visible light 400-700 $4,3×{10}^{14}$ - $7,5×{10}^{14}$ infrared 700- ${10}^{5}$ $3×{10}^{12}$ - $4,3×{10}^{19}$ microwave ${10}^{5}-{10}^{8}$ $3×{10}^{9}$ - $3×{10}^{12}$ radio waves $>{10}^{8}$ $<3×{10}^{9}$

Examples of some uses of electromagnetic waves are shown in [link] .

 Category Uses gamma rays used to kill the bacteria in marshmallows and to sterilise medical equipment X-rays used to image bone structures ultraviolet light bees can see into the ultraviolet because flowers stand out more clearly at this frequency visible light used by humans to observe the world infrared night vision, heat sensors, laser metal cutting microwave microwave ovens, radar radio waves radio, television broadcasts

1. Arrange the following types of EM radiation in order of increasing frequency: infrared, X-rays, ultraviolet, visible, gamma.
2. Calculate the frequency of an EM wave with a wavelength of 400 nm.
3. Give an example of the use of each type of EM radiation, i.e. gamma rays, X-rays, ultraviolet light, visible light, infrared, microwave and radio and TV waves.

## The particle nature of electromagnetic radiation

When we talk of electromagnetic radiation as a particle, we refer to photons, which are packets of energy. The energy of the photon is related to the wavelength of electromagnetic radiation according to:

Planck's constant

Planck's constant is a physical constant named after Max Planck.

$h=6,626×{10}^{-34}$ J $·$ s

The energy of a photon can be calculated using the formula: $E=hf$ or $E=h\frac{c}{\lambda }$ . Where E is the energy of the photon in joules (J), h is planck's constant, c is the speed of light, f is the frequency in hertz (Hz) and $\lambda$ is the wavelength in metres (m).

Calculate the energy of a photon with a frequency of $3×{10}^{18}$  Hz

1. $\begin{array}{ccc}\hfill E& =& hf\hfill \\ & =& 6,6×{10}^{-34}×3×{10}^{18}\hfill \\ & =& 2×{10}^{-15}\phantom{\rule{0.166667em}{0ex}}\mathrm{J}\hfill \end{array}$

What is the energy of an ultraviolet photon with a wavelength of 200 nm?

1. We are required to calculate the energy associated with a photon of ultraviolet light with a wavelength of 200 nm.

We can use:

$E=h\frac{c}{\lambda }$
2. $\begin{array}{ccc}\hfill E& =& h\frac{c}{\lambda }\hfill \\ & =& \left(6,626×{10}^{-34}\right)\frac{3×{10}^{8}}{200×{10}^{-9}}\hfill \\ & =& 9,939×{10}^{-10}\phantom{\rule{0.166667em}{0ex}}\mathrm{J}\hfill \end{array}$

## Exercise - particle nature of em waves

1. How is the energy of a photon related to its frequency and wavelength?
2. Calculate the energy of a photon of EM radiation with a frequency of ${10}^{12}$  Hz.
3. Determine the energy of a photon of EM radiation with a wavelength of 600 nm.

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Imeobong
An international organization is an organization with an international membership, scope, or presence.
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if a firm stays on the same isoquant it means ? a. output missteps decrease b. output must stay. the same c. output must increase d. quantity of labour and capital employed must remain the same e. none
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the law of diminishing state that as more and more variable factor is added to a fixed cost, it will increase first and later its begins to fall until its get to zero. that were ur mc equal to zero
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Bertilla
The law of diminishing demand states that, if the price of a product is raised, a smaller quantity will be demanded and if the price of a product is lowered, a greater quantity will be demanded.
Were
The law of diminishing returns, also referred to as the law of diminishing marginal returns, states that in a production process, as one input variable is increased, there will be a point at which the marginal per unit output will start to decrease, ceteris puribus
Were
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It's also the usage of mathematical tools to express and analyse economic problems.
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Economics assit in understanding the pre-requisite for Growth and developmen and how the workings of the economy operates.
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Economics is the social Science in which we study how scarce resources are allocated for the betterment of human being.
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Equilibrium point is the point at which quantity demand equals quantity supply.
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Is a strict example of an imperfect market where there is only one seller and many buyer for a particular product.
Rasaq
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Junior
opp. cost~a benefit, profit or value of something that must be given up to acquire or achieve something else
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It's a curve that reverses direction
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One of the Principle of Economics states "Market is the best place to organize economic activies". However, market may fail if it does not perform it's necessary expected functions like Exercising real forces of demand and supply, contact where transactions are made etc. Though government may int
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Rasaq
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You mean demand and supply of currency ?
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What is the difference between Demand and Quantity Demanded?
Weedh
Demand refers to how much a product is desired by buyer mean while quantity demanded refers to the amount of product a buyer is willing to buy at a certain price.
Junior
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Ogunsola
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demand is the various quantity of goods or services a consumer is Willing and able to buy at a particular price over s given period of time while quantity demanded is the amount of goods or services being paid for
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Researchers demonstrated that the hippocampus functions in memory processing by creating lesions in the hippocampi of rats, which resulted in ________.
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The fundamental frequency of a sonometer wire streached by a load of relative density 's'are n¹ and n² when the load is in air and completly immersed in water respectively then the lation n²/na is
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