Question

The electric field intensity produced by the radiation coming from the 100 W bulb at a distance 1 m is E. The electric field at distance 2 m is:

• A. $E$
• B. $2E$
• C. $\frac{E}{2}$
• D. None of these

Answer 1

Answer: (D)

None of these

Given,

$P=100W$

$E_1=E$ at $r=1m$

$E_2=?$ at $r=2m$

The electric field intensity at a distance $r$ ,

$I=\frac{P}{A}=\frac{P}{4\pi r^2}$

$I\propto \frac{1}{r^2}$

$\frac{E_1}{E_2}=(\frac{r_2}{r_1}{)}^2$

$\frac{E}{E_2}=(\frac{2}{1}{)}^2=4$

$E_2=\frac{E}{4}$

The correct option is D.