SNC2D
Ray-Tracing Activity – Converging Lens
Principal axis
SNC2D
Ray-Tracing Activity – Diverging Lens
Principal axis
SNC2D
Ray-Tracing Activity
PART A – Parts of a Converging Lens System
1. Use the three slit comb on the ray box to produce a beam of three parallel rays. Line up the
incoming rays along the principal axis. Locate the primary focus. Label this point PF.
2. Repeat this from the other side of the lens to locate the secondary focus. Label this point SF.
The two focal points should just barely fit on the page.
3. Measure the focal length, f, the distance from the centre of the lens to the primary focus.
Compare this to the distance from the centre of the lens to the secondary focus.
The focal length of this lens is: _____________.
PART B – Examining Rays for a Converging Lens
1. Use the single slit comb and aim a ray parallel to the principal axis (but not on it) that passes
through the lens. Draw its path on each side of the lens and label this ray, PARALLEL RAY.
A parallel ray passing through a converging lens will travel
__through the primary focus______________________________________________
2. Aim a ray at an angle to the principal axis so that it travels through the very center of the
lens. Draw its path on each side of the lens and label this ray, CENTRE RAY.
A centre ray passing through a converging lens will travel
___straight with no refraction______________________________________________
3. Aim a ray such that it travels through the secondary focus before reaching the lens. Draw its
path on each side of the lens and label this ray, FOCAL RAY.
A focal ray passing through a converging lens will travel
____parallel to the principal axis_______________________________________
PART C – Parts of a Diverging Lens System
1. Use the three slit comb on the ray box to produce a beam of three parallel rays. Line up the
incoming rays along the principal axis. Trace the rays on both sides of the lens. What is
different about these rays compared to those for the converging lens?
____the rays spread out (diverge), rather than come together (converge) to a point
2. How could you locate the primary focus? Take the lens off the page and trace your rays
backwards until they converge. Label the primary focus PF. Measure the focal length.
The focal length of this lens is: _____________.
What is different about the primary focus for a diverging lens system compared to for a
converging lens system?
___the primary focus is on the same side of the lens as the light source______
Homework:
Read pp. 551-553
Questions:
1. In what ways do we make use of lenses in everyday life?
Glasses, contact lenses, telescopes, magnifying glasses, cameras, microscopes
2. What is the difference between a converging lens and a diverging lens? Mention the paths of
light rays in your explanation.
Converging lens – cause parallel rays to converge to a focus,
Diverging lens – cause parallel rays to spread out
3. How many refractions actually occur as a light ray travels through a lens? Sketch a diagram
and identify the locations of these refractions.
2 refractions, 1 occurs at the air-glass interface, the other occurs at the glass-air interface
4. You are given 2 lenses: a converging lens and a diverging lens. How can you tell them apart
just by feeling their shapes?
Converging lens – thickest in the middle, thinnest at the edges (corrects far-sightedness)
Diverging lens – thickest at the edges, thinnest in the middle (corrects near-sightedness)