Module 9
PlanningGuide

Lab 3.7

Lesson 3.5
Lesson 3.6
Lesson 3.7
Lesson 3.8
Lab 3.5
Lab 3.6
Lab 3.7
Lab 3.8
Project 9

Physics Lab 3.7 Curved Mirror

Overview

In this laboratory we determine the focal point of a curved mirror and study the rules of reflection for curved mirrors.

Experiments

1. Virtual Image
2. Focal length of a concave mirror.
3. Rules and Rays

Experiment 1: Virtual Image

Equipment
Curved mirror – shaving mirror

Procedure

1. Compare the image of an object as seen in a concave mirror with that seen using a plane mirror.
2. Vary the distance between the object and the mirror and note the effect on the image.

Questions

1. Why is the virtual image magnified?
2. How does the distance between the object and the mirror affect the size and clarity of the image?

Experiment 2: Focal Length

Equipment

• Light source that can provide a narrow vertical beam
• Piece of reflective plastic mounted to provide a curved mirror
• Tape measure
• Paper

Procedure

1. Place the curved mirror on the paper and draw a line that is normal to the surface at the center of the mirror. This is called the principal axis.
2. Place the light source about 60 cm from the mirror and shine a beam parallel to the principal axis at a distance of about 6 cm from the principal axis.
3. Draw a line that coincides with this beam - the incident ray
4. Draw a second line that coincides with the reflected beam – the reflected ray.
5. Move the incident beam 1 cm closer to - and parallel - to the principal axis.
6. Repeat steps 5 and 6
7. Repeat steps 7 and 8
8. Move the light source to the other side of the principal axis ( 6 cm from the axis) and repeat steps 5 to 9
9. All of the reflected rays should converge at one point on the principal axis. This is the focal point and the distance from the mirror along the principal axis to the focal point is the focal length.

Experiment 3: Rules and Rays

Equipment

As for experiment 2 above

Procedure

1. Shine the light beam at an angle to the principal axis through the focal point onto the mirror.
2. Draw lines to mark the incident and reflected rays
3. Change the angle if incidence – the beam must still pass through the focal point.
4. Repeat steps 2 & 3

Questions

1. Are all rays that pass through the focal point reflected parallel to the principal axis?
2. Are all rays that are parallel to the principal axis reflected so that they pass through the focal point?