**Q1: **

Two electromagnetic waves propagate past a line .
The paths of the electromagnetic waves intersect at a point on a line ,
as shown in the diagram. The points of zero displacement of each wave are shown
by lines perpendicular to the directions of the paths of the wavesβ
propagation. The longer-wavelength electromagnetic wave has a wavelength double
that of the shorter-wavelength electromagnetic wave.

Are the path lengths of the two rays in the region between
and equal or unequal?

Do the phases of the waves at the point where their paths
intersect each other differ by an integer multiple of radians?

Do the phases of the waves at the point where their paths
intersect differ by an integer multiple of radians?

**Q2: **

Electromagnetic waves with a wavelength of
625 nm are
emitted from a point . The initial displacement at
is zero, which increases positively. The
waves travel to the point , as shown in the diagram.
The lengths
of the sides of the triangle in the diagram are not to scale with each other,
but the line from to is drawn to
scale with the
wavelength of the waves emitted from . The graph shows the
change
in displacement of the wave with time at the point ,
starting from
the instant at which the displacement at
starts to change, before
which it has a constant value of zero. At the instant that waves start to emit
from , waves with the same amplitude, wavelength, and phase are
emitted from the point .

What is the length of the line from to ?

What is the length of the line from to ?