Optics
Rectilinear propagation and reflection
Verify the law of reflection: the angle of reflection equals the angle of incidence measured from the normal. Drag the incidence-angle slider on the 3D flat-mirror model, read the angles in the readout, and observe the virtual image symmetric about the mirror.
⚠ In a real experiment with a laser or bright source, never look into the beam or its reflection.
Equipment
- Flat mirror and virtual light source on a 3D canvas
- Incidence-angle slider (readout in degrees)
- Refractive-index and focal-length sliders for the second ray diagram
- Normal drawn at the incidence point; angle and critical-angle readout
Procedure
Verify incidence equals reflection
In figure 1, sweep the incidence slider through 15°, 30°, 45°, 60°: the reflected ray always leaves at the same angle on the other side of the normal — read the two equal angles in the readout.
Observe the mirror image
Change the viewing angle by dragging the canvas: the virtual image of the source always sits symmetric behind the mirror at the same distance — every reflected ray's backward extension passes through it. This is how a flat mirror forms a same-size image.
Change conditions and predict rays
In figure 2, raise the refractive index below: for rays going from high to low index, read the 'critical angle' in the readout — beyond it the ray reflects totally instead of refracting. Set the incidence just below and just above to compare.