Practicing Success
Magnitude of the electric and magnetic fields in an electromagnetic wave radiated by a 200 W bulb at a distance 2 m from it is assuming efficiency of bulb is 5% and it behaves like a point source. |
12.27 N/C, 4.09 × 10-8 T 10 N/C, 10-5 T 11.7 N/C, 5 × 10-6 T 5 N/C, 104 T |
12.27 N/C, 4.09 × 10-8 T |
Effective power of the bulb, $P=\frac{5}{100} \times 200=10 W$ Intensity at distance r is given by $I=\frac{P}{4 \pi r^2}=\frac{10}{4 \times 3.14 \times 2^2} W / m^2=\frac{10}{16 \times 3.14} W / m^2$ $=0.199 W / m^2=0.2 W / m^2$ $I=\frac{1}{2} \varepsilon_0 E_0^2 c$ $E_0^2=\frac{2 I}{c \times \varepsilon_0}$ $\Rightarrow E_0=\sqrt{\frac{2 I}{c \times \varepsilon_0}}$ $\Rightarrow E_0=\sqrt{\frac{2 \times 0.2}{3 \times 10^8 \times 8.85 \times 10^{-12}}} \Rightarrow E_0=12.27 N / C$ $\Rightarrow B_0=\frac{E_0}{c}=\frac{12.27}{3 \times 10^8}=\frac{12.27}{3} \times 10^{-8} T=4.09 \times 10^{-8} T$ |