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A laser beam has intensity 2.5 × 10^{14} W m^{−2}. Find amplitudes of electric and magnetic fields in the beam.

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#### Solution

Given:

Intensity, I = 2.5 × 10^{14} W/m^{2}

We know :

`I = 1/2 ∈_0 E_0^2 c`

⇒ `E_0^2 = (2I)/(∈_0c)`

⇒ `E_0 = sqrt((2I)/(∈_0c))`

⇒ `E_0 = sqrt((2 xx 2.5 xx 10^14)/(8.85 xx 10^-12 xx 3 xx 10^8))`

⇒ `E_0 = 0.4339 xx 10^9`

⇒ `E_0 = 4.33 xx 10^8 "N/C"`

Maximum value of magnetic field ,

`B_0 = (E_0)/c`

`B_0 = (4.33 xx 10^8)/(3 xx 10^8)`

⇒ `B_0 = 1.43 "T"`

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