# Physics

Name Date Class

Lab 26: Reﬂection and Refraction of Light

Purpose

To compare the reﬂection of light from ﬂat and curved mirrors and to study the refraction of light through a lens

Background

What is the difference between a mirror and a lens? Light bounces, or reﬂects, off a mirror but passes through a lens. Mirrors and lenses have many different uses due to these properties. Mirrors are often used to allow people to see their

reﬂections or to see things in places or at angles that you couldn’t see otherwise. Lenses are used commonly to magnify images, correct vision, or to focus light into a beam. These properties have been used for centuries as people discovered reﬂective surfaces and developed the ﬁrst cameras and spectacles.

Skills Focus

Predicting, observing, applying concepts, controlling variables, drawing conclusions

Procedure

1. Start Virtual Physics and select Reﬂection and Refraction of Light from the list of assignments. The lab will open in the Optics laboratory.

2. The laboratory will be set up with a light bulb on an optics table with a ﬂat mirror in front of it. An eye will be set up on the table to be used as a

detector, to observe how light is reﬂected from the mirror. You will observe reﬂected light from various angles to determine how images are reﬂected in

a ﬂat mirror. You will then compare those to the reﬂections from curved mirrors. You will also study how light refracts through lenses.

3. Predicting What do you think you will see in the detector window if it is facing the direction of the reﬂected light?

4. Observing What do you notice about the relationship between (1) the

angle of the light coming in to the mirror relative to the normal, which is a line perpendicular to the mirror ’s surface, and (2) the angle of the light

reﬂecting off the mirror? Hold up a piece of paper on the screen and position

it as the normal would be to help you compare the angles.

Reﬂection and Refraction of Light 83

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5. Change the angle of the light striking the mirror by rotating the mirror. You

can do this by moving the cursor over the mirror until a rotation control appears and increasing the angle by dragging the cursor in the direction you want the mirror rotated, or by clicking on the arrows. Now compare the

angle of the incident light (the light striking the mirror) with the angle of the reﬂected light. How have the angles changed?

6. Applying Concepts The law of reﬂection explains the phenomenon that

you just observed—that the angle of incidence always equals the angle of reﬂection. Do you think this will change if the mirror is a curved mirror? Predict how the angle of reﬂection will compare with the angle of incidence

if the mirror is curved.

7. Test your prediction by right clicking on the mirror and unchecking the Flat

box and changing the radius of curvature (r) to 60 cm. This is a concave mirror, which is what is used in a ﬂashlight to focus light into a narrow beam of light. Record your observations of the angle of reﬂection and the beam diameter below.

8. Now change the mirror into a convex mirror by altering the radius of

curvature to -50 cm. Note your observations of the angle of reﬂection and the beam diameter below.

9. Observing Now you will observe refraction with a lens. Pick up the

detector and drag it off the table to return it to the counter. Change the

mirror back into a ﬂat mirror by clicking the Flat box. Pick up another mirror and place it on the table in the beam path reﬂected off the ﬁrst mirror. Rotate the second mirror to an angle of around 0 degrees, where it reﬂects the light down at an angle onto the table, just not facing directly along a line of pins. Pull out a lens and place it in the beam path. What do you observe about the incident angle of the light on the lens and the angle of the transmitted light

on the other side of the lens?

84 Reﬂection and Refraction of Light

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10. Light is refracted, or bent, as it travels through lenses of different materials.

What is the index of refraction of the lens? The index is found in the lens variable panel by right clicking on the lens and noting the value of n. The index of refraction of air is approximately 1.

11. Change the index of refraction to 1 and report how the transmitted angle

changes from the previous deﬂection.

12. Controlling Variables Increase the index of refraction gradually from 1 to

10 and report on how the deﬂection angle changes.

13. Drawing Conclusions Click the Reset Lab button in upper left corner to

clear the table. Pull down the prism platform and release and it will snap into place on the table. Bring down the light bulb also and release it on the left side of the table. Click on the bottom prism on the stand and pull it

down to the bottom of the base. Observe the way the beam of light bends

as it passes through the ﬁrst prism and then on to the second prism. Describe what you observe from what you understand about refraction.

Mention how the light bends with respect to the normal for each face of the prism.

Reﬂection and Refraction of Light 85

ISBN 0-558-83901-0

ISBN 0-558-83901-0

ISBN 0-558-83901-0

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