A $4.4 \times 10^{14} \mathrm {~Hz}$ Laser Emits A $2.1 \mu$ S Pulse That Is

Multiple Choice

A $4.4 \times 10^{14} \mathrm {~Hz}$ laser emits a $2.1 \mu$ s pulse that is $5.0 \mathrm {~mm}$ in diameter. The energy density in the beam is $0.24 \mathrm {~J} / \mathrm { m } ^ { 3 }$ . How many wavelengths are there in the length of the beam? $\left( c = 3.0 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s } \right.$ , $\mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm {~T} \cdot \mathrm { m } / \mathrm { A } , \varepsilon _ { 0 } = 8.85 \times 10 ^ { - 12 } \mathrm { C } ^ { 2 } / \mathrm { N } \cdot \mathrm { m } ^ { 2 }$ )

A) $2.8 \times 10 ^ { 9 }$
B) $9.2 \times 10 ^ { 9 }$
C) $2.8 \times 10 ^ { 8 }$
D) $9.2 \times 10 ^ { 8 }$
E) $2.8 \times 10 ^ { 10 }$