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Structure of Atom — Chemistry STD 11 Science — Question

Maharashtra BoardEnglish MediumSTD 11 ScienceChemistryStructure of Atom6 Marks
Question
Define and explain the following terms:
$i.$ Wavelength $(\lambda)$.  $ii.$ Frequency ( $v$ ) $iii.$ Wavenumber $(\bar{v})$  $iv.$ Amplitude $(A)$  $v.$ Velocity $(c)$
✓

Answer

$i.$ Wavelength $(\lambda)$ :
The distance between two consecutive crests or two consecutive troughs in a wave is called wavelength. $-$
It is represented by Greek letter $\lambda ($lambda$).$
The $\text{SI}$ unit for wavelength is metre $(m).$
Note: The other units include Angstrom, nanometre, picometer $\left(1 \ \mathrm{pm}=10^{-12} \mathrm{~m}\right.$ ) and micron $\left(1 \mu=10^{-6} \mathrm{~m}\right)$.$ 1 \mathring A =10^{-8} \mathrm{~cm}=10^{-10} \mathrm{~m}$
$ 1 \mathrm{~nm}=10^{-9} \mathrm{~m}=10 \mathring A $
$ii.$ Frequency $(ν):$
The number of waves that pass a given point in one second is called frequency.
It is represented by Greek letter $‘ν \ ’ (nu).$
The $\text{SI}$ unit of frequency is Hertz $(Hz) \ or \ s^{-1}.$
Note $: 1 Hz = 1$ cycle per second $(1 cps)$
The units, kilo Hertz $(kHz)$ and mega Hertz $(mHz)$ are commonly used.
$1 \ kHz = 10^3 Hz = 10^3 \ cps$
$1 \ mHz = 10^6 Hz = 10^6 \ cps$
$iii.$ Wavenumber $(\bar{v})$ :
The number of wavelengths per unit length is called the wavenumber.
It is represented by $\bar{v} ($nu bar$).$
The commonly used unit for wavenumber is $\mathrm{cm}^{-1}$ while its $\mathrm{Sl}$ unit is $\mathrm{m}^{-1}$.
Wavenumber of a wave is related to the wavelength as follows: $\bar{v}=\frac{1}{\lambda}$
$iv.$ Amplitude $(A):$
The height of a crest or the depth of a trough from the line of propagation of the wave is called
amplitude.
It is represented by letter $‘A \ ’.$
The square of the amplitude represents the intensity $($brightness$)$ of the radiation.
$v.$ Velocity $(c):$
The distance travelled by a wave in one second is called the velocity of the wave.
It is denoted by letter $c.$
It is the product of the frequency and wavelength. Hence, $c = ν\lambda$
The velocity of all types of electromagnetic radiations $($in space or in vacuum$)$ is the same and it is equal to the velocity of light $(3 \times 10^{10} \ cm s^{-1} \ or \ 3 \times 10^8 \ m s^{-1}.$ However, they may have different wavelengths and frequencies.

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