ICSE Physics Class 7 Notes Chapter 4 Light
→ Light is a form of energy which helps us to see objects.
→ Light always travels in a straight line in the form of rays.
→ Light sources are either natural or artificial.
→ The sun and stars are natural sources of light.
→ A bulb, a candle etc. are artificial sources of light.
→ The bodies which emit light themsleves are called Luminous Bodies, e.g. sun, star.
→ The bodies which do not emit light are called non-luminous bodies, e.g. wood, brick etc.
→ Objects are of three types, transparent, translucent or opaque.
→ The pinhole camera is a simple application of the rectilinear propagation of light.
→ When an object blocks light, it casts a shadow.
→ Eclipses are formed due to formation of shadows.
→ Solar and lunar eclipses are the examples of formation of shadow in nature.
→ An eclipse is the partial or complete hiding of one heavenly body by shadow of another.
→ When light strikes a polished surface it comes back in the same medium, is called reflection of light.
→ A straight highly polished, smooth and reflecting surface is known as a plane mirror.
→ Mirrors are of two types –
(a) plane mirrors
(b) spherical mirrors.
→ Smooth and polished surface like a mirror causes reflection and is called a regular reflection.
→ Rough or diffused surface causes an irregular reflection.
→ According to first law of reflection. The incident ray, the normal and the reflected ray all lie in the same plane.
→ According to the second law of relection, the angle of incidence is always equal to the angle of reflection.
→ The phenomenon due to which the left side of an object appears to be the right side of the object and right side appears left. This is known as lateral inversion.
→ Image is of two types –
(a) Real image
(b) Virtual image.