Reflection

1. What happens to light when it hits a reflective surface?

When light hits a reflective surface, it bounces off that surface. The type of reflection that occurs
depends on the smoothness of the surface. If the surface is smooth, like a mirror, the light is
reflected in a single direction, which is called specular reflection. If the surface is rough, like
paper or a wall, the light scatters in many directions, which is called diffuse reflection.

2. Which material is best at reflecting light: metal or glass? Explain how you worked out
your answer.

Metal is the best material for reflecting light. This is because mirrors are typically made of glass
with a thin metallic coating on the back. The metal layer is smooth and highly reflective, which
allows it to reflect light efficiently. Glass, on the other hand, reflects some light but is not as
effective as metal.

3. Why can’t you see an image reflected by a piece of paper?

You can't see an image reflected by a piece of paper because paper has a rough surface,
causing diffuse reflection. This means that the light bounces off in many directions, scattering
the light and preventing the formation of a clear, focused image.

4. Explain why you can see your reflection better in a piece of metal if you polish the
surface.

When you polish a metal surface, you make it much smoother. A smooth surface reflects light in
a uniform direction (specular reflection), allowing a clear, focused image to form. Without
polishing, the metal surface would be rough and cause , making it difficult to see a sharp
image.

5. Light hits a plane mirror with an angle of incidence of 20°. What will the angle of
reflection be?

According to the law of reflection, the angle of reflection will be equal to the angle of
incidence. So, if the angle of incidence is 20°, the angle of reflection will also be 20°.

6. You stand 2 meters in front of a plane mirror. Explain how far you are from where the
image appears to be.

The image in a plane mirror will appear to be the same distance behind the mirror as you are in
front of it. If you stand 2 meters in front of the mirror, the image will appear to be 2 meters
behind the mirror. So, you are a total of 4 meters away from the image (2 meters in front of the
mirror and 2 meters behind it).

7. Suggest why the lines on the right-hand side of diagram D are shown as dotted lines.

The dotted lines in diagram D are used to represent the virtual image formed in a plane mirror.
A virtual image is one that cannot be projected onto a screen because the light rays do not
actually meet at the location where the image appears to be. The dotted lines show the
apparent direction from which the light rays seem to be coming.
8. Is the reflection of the water in photo F specular or diffuse reflection?

The reflection of the water in photo F is most likely specular reflection, provided the surface of
the water is calm and smooth. Specular reflection occurs when light is reflected in a single,
consistent direction, which happens when the surface is smooth, like still water.

9. Draw a ray diagram to show how light coming from the sky forms an image of the
vehicle in the water.

In a ray diagram for specular reflection, the light from the vehicle hits the surface of the water
(the reflective surface), and the light is reflected back towards an observer’s eyes. The incident
ray forms an angle with the normal (the imaginary line perpendicular to the surface), and the
reflected ray forms the same angle with the normal, allowing an image of the vehicle to form.

10. Explain why you will not see an image of the vehicle in the water on a windy day.

On a windy day, the surface of the water becomes rough due to ripples or waves. This causes
diffuse reflection rather than specular reflection, scattering the light in all directions. As a
result, you will not see a clear image of the vehicle because the light is no longer reflected in a
focused way.

11. Describe how mirrors and rough surfaces reflect light.

 Mirrors: Mirrors reflect light through specular reflection, which happens when the
surface is smooth. The reflected rays travel in a predictable direction, forming a sharp,
clear image.

 Rough surfaces: Rough surfaces reflect light through diffuse reflection. The light rays
scatter in many different directions because the surface is uneven. This type of reflection
does not form a clear image.

12. Describe how an image is formed in a mirror using a ray diagram.

To form an image in a mirror:

1. Incident rays: Light rays from an object strike the mirror at various angles.

2. Reflection: The light rays reflect off the mirror, with the angle of incidence equal to the
angle of reflection.

3. Virtual image: The reflected rays appear to come from a point behind the mirror
(although they don’t physically meet there). This creates a virtual image that is the same
size as the object, with the left and right reversed.
Refraction

1. What is refraction?

 Refraction is the change in direction of light when it passes from one transparent
material (like air) into another (like water or glass). This happens because light travels at
different speeds in different materials. When light slows down (as it does when it enters
a denser material like glass or water), it bends towards the normal (the imaginary line
perpendicular to the surface), and when it speeds up again (leaving the material and
returning to air), it bends away from the normal.

2. Why are lenses needed in:

 a) Cameras: Lenses are used in cameras to focus light and make the image sharp.
They allow light from different parts of a scene to come together to form a clear image
on the camera sensor.

 b) Telescopes: In telescopes, lenses are used to gather and focus light from distant
objects, making them appear closer and clearer.

 c) Microscopes: Lenses in microscopes help to magnify tiny objects, allowing us to see

3. Draw a ray diagram to explain the following terms:

 a) The normal: The normal is an imaginary line that is perpendicular to the surface
where light is entering or leaving a material (like a lens or a glass block).

 b) The angle of incidence: This is the angle between the incident ray (incoming light)
and the normal.

 c) The angle of refraction: This is the angle between the refracted ray (the light after it
bends) and the normal.

Ray Diagram Explanation:

 Imagine a light ray approaching a glass block. The ray hits the block at an angle (angle
of incidence). The ray then bends towards the normal as it enters the block (because the
light slows down in glass). When the light exits the block, it bends away from the normal,
and the angle of refraction is measured between the refracted ray and the normal.

4. Describe how to compare the angles of incidence and refraction for a ray of light
entering a glass block:

 To compare the angles of incidence and refraction, you can use a ray box to shine light
at a glass block. Mark the points where the light enters and leaves the block, and draw a
straight line through these points. The angle between the incoming ray and the normal is
the angle of incidence, and the angle between the outgoing ray and the normal is the
angle of refraction. You can compare the two angles to observe how the light bends.
5. Explain why an object in water appears to be closer than it really is (based on
diagram D):

 The reason an object in water appears closer than it really is, as shown in diagram D, is
due to refraction. Light from the object in the water bends as it passes from water (a
denser medium) into air (a less dense medium). This bending causes the object to
appear at a different position than where it actually is. The light rays are refracted as
they exit the water, making the object appear closer to the observer.

6. Describe the shape of a converging lens:

 A converging lens is thicker in the middle than at the edges. It is typically a biconvex
lens, meaning it has two outward curving surfaces. The lens focuses parallel rays of
light to a single point called the focal point.

7. How does a converging lens work (using a model)?

 A converging lens works by bending incoming light rays towards a focal point. Light
entering the lens bends towards the normal as it enters the lens, and bends away
from the normal as it exits the lens. Because of the shape of the lens, the light rays are
focused at a single point (the focal point), which is the location where the image is
formed.

8. What would happen to rays of light if they shone through a lens fatter than the one in
diagram E? Draw a diagram similar to diagram E to work out the answer.

 If the lens is fatter (i.e., has a larger curvature), the light rays would be bent more sharply
and would meet at a focal point that is closer to the lens. The focal length of a thicker
lens is shorter than that of a thinner lens.

9. Would this fatter lens have a longer or shorter focal length than the lens in diagram E?

 A fatter lens would have a shorter focal length because the curvature of the lens
causes it to bend the light rays more sharply, bringing them to a focal point closer to the
lens.

10. How can a converging lens be used in a theatre spotlight to make a parallel beam of
light? Include a diagram.

 A converging lens can be used in a spotlight by placing the light source at the focal
point of the lens. When the light rays pass through the converging lens, they are bent in
such a way that they exit the lens as parallel rays. This produces a focused, parallel
beam of light, which is ideal for spotlighting.

11. Diagram Explanation:

 The light source (like a bulb) is placed at the focal point of the converging lens. The rays
from the bulb pass through the lens, and the lens bends the rays so that they exit
parallel to each other.