Ahhhh wat do i do please help!! this lightwaves are making me soo confused..

Question

ahhhh wat do i do please help!! this lightwaves are making me soo confused..

Modern lasers can create a pulse of light that lasts only a few femtoseconds.

(a) What is the length of a pulse of violet light that lasts 6.2 fs?

___ m

(b) How many wavelengths of violet light (λ = 400 nm) are included in such a pulse?

Answer 1

The light emitted from the laser travels at "the speed of light".  The length of the pulse required for part a is the distance traveled by the light emitted when the laser was turned on in the time the pulse lasted.

The speed of light is 2.99*10^8 m/s.  1fs is 1*10^-15 seconds.  The total distance traveled by light in 10fs is 2.99*10^-6 m which is 2.99um (which is 2990nm).  You have to change the number for 6.2fs.

Since violet light is 400nm, you can figure out how many wavelengths are in a pulse by comparing it to the distance travlled.  For a 10fs pulse, that distance is 2990nm.  400nm fits into 2990nm 7 times (with some remainder).