Greer bounces a laser beam off a locker mirror onto the far wall and marks the bright spot. She tilts the beam a little, and the spot jumps. Where the spot lands is not random.
In the waves topic, you predicted a reflected wave's path: it leaves at the same angle it arrived, measured from the normal. This lesson re-uses that prediction for light rays and gives it its name.
Greer's beam arrives at the mirror at 30° from the normal.
The reflected beam leaves at 30° from the normal, on the other side of the normal.
This rule is called the law of reflection.
Both angles are always measured from the normal, never from the surface.
Light arriving along the normal reflects straight back along the normal: the two equal angles are both 0°.
In earlier grades you saw that light meeting a surface can be reflected, absorbed, or transmitted; the law of reflection tracks the reflected part.
Any flat mirror obeys the same rule: in at some angle from the normal, out at the same angle on the other side.
A ray hits a flat mirror at 55° from the normal. Give the reflected ray's path.
The angle of reflection equals the angle of incidence.
The angle of incidence is 55°, so the angle of reflection is 55°.
The reflected ray leaves on the other side of the normal.
The reflected ray leaves at 55° from the normal, on the other side of the normal.
Fintan shines a flashlight straight down a well, along the normal to the still water's surface. Which way does the reflected light go?
Arriving along the normal, the angle of incidence is 0°.
The angle of reflection equals it, so the angle of reflection is 0°.
An angle of 0° from the normal is the normal itself.
The reflected light goes straight back up the well.
A ray strikes a flat mirror at 48° from the normal. Enter the angle of reflection, in degrees.
A laser beam arrives at a flat mirror at 62° from the normal. Which description gives the reflected beam?
Elowen shines a flashlight straight at a hallway mirror, along the normal. She says the beam reflects straight back toward her. Is Elowen correct?
Which statement is the law of reflection?
Moonlight strikes a still lake at 15° from the normal. Enter the angle, in degrees, between the reflected light and the normal.
Sunlight comes down at 35° from the normal onto the flat glass cover of a solar panel. Which description gives the reflected glare beam?