Grade 10: Mirrors and Lenses

Grade 10: Mirrors and Lenses

How do you see yourself in a mirror? How do you compare the way you look and the way your image look? Can you explain how your image is formed on the mirror? This new lesson will lead you to the answer to these questions. 

OPTICS

is a branch of Physics which deals with the study of light, mirrors, and lenses 

Learning Competencies

• Predict the qualitative characteristics (orientation, type, and magnification) of images formed by plane and curved mirrors and lenses

•  Identify ways in which the properties of mirrors and lenses determine their use in optical instruments (e.g., cameras and binoculars)

Multiple Choice

1. A clock hang on the wall is facing a plane mirror hanged on the opposite wall. As you see the reflection of the clock on the mirror, the clock shows the time of 9:00. What is the real time?

• A. 2:00

• A. 3:00

• A. 4:00

• A. 5:00

Multiple Choice

2. If a man stands 4 feet in front of a plane mirror, how far away is the man’s image from the mirror?

• A. Nearer than the man from the mirror

• B. Twice as far as the man from the mirror

• C. Three times as far as the man from the mirror

• D. The same distance as the man from the mirror

Multiple Choice

3. How do you describe the kind of the image shown on the given illustration?

• A. Real image

• B. Virtual image

• C. Both a and b

Multiple Choice

4. On the given illustration, which is the incident ray?

• A. A

• B.B

• C.C

• D.D

Multiple Choice

5. In a plane mirror, how does the reflected image appear?

• A. Slightly out of focus

• B. Closer than the actual object

• C. Upright and the same size as the object

• D. Upside down and much smaller than the object

What do you think will happen if light hits a mirror?

• When light hits a mirror, it reflects or bounces off the mirror’s surface.

Simple Activity

Mirror...mirror on the wall!

REFLECTION

• Reflection is the turning back/bouncing of light rays when it hits a shiny surface like a mirror

3 Imaginary Rays

• Reflected Ray- is the ray from the reflecting surface

• Normal Line (N)- is the line which is perpendicular to the mirror

•  Incident Ray- is the ray of light approaching the mirror

 Laws of Reflection

• When a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection

• The angle between the normal line and the reflected ray is the angle of reflection

• angle of incidence (θi)- is the angle between the incident ray and the normal line

• angle of reflection (θr)- is the angle between the reflected ray and the normal line 

2 types of Reflection

• Specular/ Regular Reflection

• Diffused/ Irregular Reflection

Specular/ Regular Reflection

• is a reflection of light on smooth surfaces such as mirrors or a calm body of water

How does specular/regular reflection occur?

• It occurs when the reflected rays are pointing in one direction

Diffuse/Irregular Reflection

• is the reflection of light on rough surfaces such as on a wavy body of water, clothing, paper, and the asphalt roadway.

How does diffuse/irregular reflection occur?

• occurs when the reflected rays are pointing in different directions

Check Your Understanding about Specular and Diffuse Reflection

• If a bundle of parallel incident rays undergoing diffuse reflection follow the law of reflection, then why do they scatter in many different directions after reflecting off a surface?

• Answer: Each individual ray strikes a surface which has a different orientation. Since the normal is different for each ray of light, the direction of the reflected ray will also be different.

Check Your Understanding about Specular and Diffuse Reflection

• Perhaps you have observed magazines which have glossy pages. The usual microscopically rough surface of paper has been filled in with a glossy substance to give the pages of the magazine a smooth surface. Do you suppose that it would be easier to read from rough pages or glossy pages? Explain your answer.

• Answer: It is much easier to read from rough pages which provide for diffuse reflection. Glossy pages result in specular reflection and cause a glare. The reader typically sees an image of the light bulb which illuminates the page. If you think about, most magazines which use glossy pages are usually the type which people spend more time viewing pictures than they do reading articles.

MIRRORS

What do you see when you look at a mirror and a spoon?

• You can see your image. Why?

• These objects are image reflecting objects. A mirror is a smooth reflecting surface, usually made of polished metal or glass that has been coated with metallic substances.

• There are two types of mirrors: a plane mirror and a curved mirror.

2 Kinds of Mirror

• Plane Mirror

• Curved/ Spherical Mirrors (Concave and Convex)

Plane Mirror

• is flat, smooth surface that reflects light in a regular way

Plane Mirror

• also applies the Left-right Reversal

Multiple Images

• are formed by the reflection that happens when arranging at least 2 mirrors

Identify the ff:

• kind of image

• position

• size

• location

• Kind of Image: either virtual or real

• Position: either upright or inverted

• Size: smaller, bigger, the same size as the object

• Location: Regardless of where the observer is located, when the observer sights at the image location, the observer is sighting along a line towards the same location that all other observers are sighting.

Plane mirror

• What image is formed?

• Virtual image. Why? 

• Because when we look into a plane mirror, it seems that our image is formed and is present somewhere behind the mirror

Basically, no light reaches the behind the mirror, thus it is always said that rays appear to meet somewhere, as it is simply the perception of the viewer.

As we can see here that light rays actually get focused at a certain position. And at that particular position, a visible image of that object is formed. It is to be noted here that after converging at a point, the rays get diverged from that particular point.

is/are a reflecting surface in which its surface is a section of sphere 

A. Concave Mirror

• A concave mirror produces both real and virtual images, which can be upright or inverted. The size of the image can be bigger or smaller than the object. The nature, size, and position of the image depend on the position of the object.

B. Convex Mirror

is a curved mirror in which the reflective surface bulges outward or toward the light source

Why AMBULANCE is written as ECNALUBMA on emergency vehicles?

• Most drivers will view the ambulance in their rear-view mirrors. As such, they will be viewing an image of the lettering. Such images appear with left-right reversal and so will be viewed with the proper orientation - AMBULANCE.

 Do the following Learning Tasks

•   a. Learning Task no. 1 Image in a Plane Mirror p. 23

•   b. Learning Task no. 3 Image in spherical mirrors p. 24

•  c. Learning Task no. 2 Image at Different Positions of the Object from the Lens pp. 28-29

Dothe following:

• Learning Task no. 4 (Performance Task no. 3) found in your weekly home learning plan dated Feb. 18 (soft copy is attached in your Google Classroom)

• Answer the 10-item quiz through Google forms in your Google Classroom

References

• https://www.youtube.com/watch?v=_HAfRsX6v0Q&t=432s

• https://www.physicsclassroom.com/Physics-Interactives/Reflection-and-Mirrors

• https://byjus.com/physics/difference-between-real-image-and-virtual-image/

• https://autojosh.com/why-is-the-word-ambulance-spelt-backwards-on-emergency-vehicles/

• https://www.youtube.com/watch?app=desktop&v=Poq3u7BFhqk