PASCO WA-9899 Ripple Tank System - Manual (Page 11)

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M o d e l N o . W A - 9 8 9 9 E x p e r i m e n t 1 : R e f l e c t i o n
11
Experiment 1: Reflection
Purpose
The purpose of this activity is to study the reflection of a plane wave from different
shaped barriers: a long straight barrier and a curved barrier.
Theory
A ray is a line that indicates the direction of motion of a plane
wave. Wave fronts are perpendicular to the ray. When a wave
reflects from a surface, the angle of incidence is the angle
between the incoming (or incident) ray and the normal (a line
perpendicular to the surface). The angle of reflection is the angle
between the outgoing (reflected) ray and the normal.
Setup
1. Mount the light source onto its rod at the back edge of the
ripple tank.
2. Pour a small amount of water into the tank and adjust the feet on the legs of the
tank to level the tank.
3. Place the long straight barrier in the middle of the tank and add about 800 mL of
water to the tank (or enough water so that the water level is about halfway up the
long straight barrier.)
4. Use a rod and base to support the ripple generator and position the generator over
the midpoint of one side of the ripple tank. Plug the light source into the ripple
generator and connect the ripple generator to its power adapter.
5. Connect the plane wave dipper to the ripple arms. Adjust the ripple generator
until the bottom of the plane wave dipper is barely in contact with the surface of
the water.
6. Place a sheet of paper directly under the ripple tank so you will be able to sketch
the images of the waves that are projected onto the sheet by the light source.
Equipment from Ripple Tank System
Ripple Tank Ripple Generator and Light Source
Long Barrier Plane Wave Dipper
Curved Barrier Ruler
Other Equipment and Materials
Large Rod Stand (ME-8735) Protractor
90-cm Rod (ME-8738) Drawing compass
Paper (about 40 cm by 40 cm)
reflected ray
Figure 1.1: Definition of Angles
incident ray
wave front
normal
θ
i
θ
r
Tip: Make sure that
the plane wave dip-
per is in contact
with the water
evenly over its
length.
Water appears to
curve upward on the
sides of the plane
wave dipper