Characteristics of an image formed by a plane mirror

The image:
1. has same size as object
2. is virtual
3. is laterally inverted
4. distance equal to the object distance from the mirror
5. is erect or upright

Characteristics of image formed in a pinhole camera

(i) The image formed is real because it is visible on the screen

(ii) It is inverted

(iii) It is generally smaller/diminished than the size of the object

Eclipse

The earth, along with the other planets, revolves around the sun in its orbit. In turn, the moon revolves around the earth in the moon’s orbit. There comes a time when the three heavenly bodies get aligned in the same straight line. This is when an eclipse occurs. It is defined as an astronomical phenomenon that occurs when one spatial object comes within the shadow of another spatial object. This obstructs the observer from seeing one of them in space. On earth, we witness two types of eclipses: solar and lunar.

Solar Eclipse

Also known as the eclipse of the sun, it occurs when the moon comes in between the sun and the earth. As a result, the moon blocks the light of the sun from reaching the earth's surface and casts a shadow on it. This occurs in a new moon phase.

Lunar Eclipse

Also known as the eclipse of the moon, it occurs when the earth comes in between the sun and the moon. As a result, the earth blocks the light of the sun from reaching the moon’s surface and casts its shadow on the moon. It occurs on a full moon day.

A natural source of light is light that occurs naturally without the involvement of humans.

Natural sources of light can come from either an object or a living species.

Examples include the moon, Sun, stars, lightning, jellyfish, fireflies, glowworms, angler fish, etc.

Characteristics of image formed in a pinhole camera

(i) The image formed is real because it is visible on the screen

(ii) It is inverted

(iii) It is generally smaller/diminished than the size of the object

Angle of incidence = Angle of reflection

Angle to the surface of a plane mirror + angle of incidence = 90°

30° + angle of incidence = 90°

Angle of incidence = 90° - 30° = 60°

Angle of reflection = 60°

Angle of incidence = Angle of reflection

20^o + Angle of incidence = 90^o

Angle of incidence = 90 - 20
Angle of incidence = 70^o

Angle of incidence = Angle of reflection
Angle of reflection = 70^o

Characteristics of image formed by a plane mirror

1. The image formed by a plane mirror is virtual and erect.
2. The image formed by a plane mirror is of the same size as the object.
3. The image is formed behind the mirror and the distance of the image from the mirror is equal to the distance of the object from the mirror.

Distance between the object and the image = Object distance + image distance
Distance between the object and the image = 20 cm + 20 cm = 40 cm

20^o + i = 90^o

i = r

Where i= angle of incidence and r = angle of reflection.

20^o + i = 90^o

i = 90 - 20
i = 70^o

i = r = 70^o

Concave Lenses are for the short sightedness and convex for the long sightedness.

Refraction is the bending of light (it also happens with sound, water and other waves) as it passes from one transparent substance into another. This bending by refraction makes it possible for us to have lenses, magnifying glasses, prisms and rainbows. Even our eyes depend upon this bending of light.

When a ray of light approaches a smooth polished surface and the light ray bounces back, it is called the reflection of light. The incident light ray that land on the surface is reflected off the surface. The ray that bounces back is called the reflected ray.

Moon doesn't have its own light and it either reflects or refracts the light of the sun. Hence it can be said that the moon is not the natural source of light.

Light travels in a straight line

From the above experiment when one of the cardboard sheets is moved to either side, it is observed that the flame is no longer visible. This is because the light cannot bend to pass through the hole.

Examples of Straight-Line Motion of Light

1. When a lamp, torch, or another source of light emits light, it travels in a straight line

2. When sunlight enters a dusty environment through tiny holes, a straight-line trail of light is apparent

3. The object will become invisible when an opaque object is placed in front of it. The reason for this is that an opaque object prevents light from bending through its corners

Properties of image formed on a plane mirror

1. The image obtained is virtual.
2. The image is laterally inverted.
3. The image is erect.
4. The size of the image is the same as the size of the object.
5. The distance between the image obtained is the same as the distance between the object from the mirror.

Glow worm

Characteristics of image formed in a pin-hole camera

1. The image formed is real hence it can be formed on the screen
2. It is inverted
3. It is generally smaller than the size of the object

How Shadows Are Formed

An opaque object blocks the light falling on it. This creates an area of darkness on the side of the object away from the source of light.

A translucent object also creates a faint area of darkness.

An area of darkness formed by an opaque object obstructing light is called a shadow.

The following three things are required for a shadow to form:
1. a source of light
2. an opaque object
3. a screen or surface behind the object.