# Nature of electromagnetic radiation and Photoelectric effect

### Nature of Light : Different Theories

Newton's Corpuscular Theory :
Light comes out of the source as small particles called corpuscles. It traces in straight lines.

Huygen's Wave Theory :
According to Huygen, light has wave character. He compared light with mechanical waves. Maxwell's Electromagnetic Theory :
A reaction which consists of both electric and magnetic components which are perpendicular to each other and perpendicular to direction of propagation of light Wave length (λ) :  Units cm/s ; m/sec

Frequency(ν) : \tt \nu = \frac{C}{\lambda}
units Hz (or) Cps (or) S-1
eg : λ400nm = 400 × 10-9 = 4 × 10-7 m

wave number ( \overline{\nu}) :
\overline{\nu} = \frac{1}{\lambda}
units = cm-1 (or) m-1

Velocity of light (c) :
C = 3 × 108 m/s (or) 3 × 1010 cm/sec Amplitude (A) : I ∝ a2
I = Intensity

Electromagnetic spectrum : Photo electric effect : The emission of electrons by a metal surface when a radiation having same frequency
h\nu = W + KE \ \ \ \ \ \ \ \ KE = \frac{1}{2}mv^{2}
W → Work function (The amount of energy required to free the electron from the metal surface)
W = hν0 → The minimum frequency
ν0 = Threshold frequency → The minimum frequency required to free the electron. ### Part2: View the Topic in this video From 0:40 to 43:40

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1. Frequency = \tt V=\frac{C}{\lambda}

2. Wavelength = \tt \lambda=\frac{C}{V}

3. Wave number = \tt \overline{v}=\frac{1}{\lambda}, v=\frac{c}{\lambda}=c\overline{v}

4. Time period \tt T=\frac{1}{\upsilon}

5. No. of waves \tt n=\frac{2\pi r}{\lambda}\left(where \ \lambda=\frac{h}{m\upsilon}\right)

6. No. of revolutions of e- per second is =\tt \frac{\upsilon}{2\pi r}