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E-STAR - Student

Home Physics PHYSICS: A Textbook for Grade 11   Chapter 6: Light

E-Lecture - Important Points
  • Light is a form of energy that enables us to see objects surrounding us, it causes the sensation of vision.
  • The speed of light in vacuum is 300,000,000m/s. The speed of light is different in different media.
  • Light is dualistic in nature, it behaves both as a particle and as a wave
  • Objects which are capable of emitting their own light are called Source of light.
  • Objects which do not emit light but reflect the light from luminous objects are called non-luminous objects.
  • Natural light sources produce light naturally without any human involvement, but artificial sources of light are constructed by humans.
  • Reflection is the phenomenon in which light travelling in one medium, incident on the surface of another returns to the first medium.
  • Refraction is a phenomenon in which there is a change in the speed of light as it travels from one medium to another and there is a bending of the ray of light.
  • When light travels from a denser medium to a lighter medium, it speeds up and the light bends away from the normal.
  • When light travels from a lighter medium to a denser medium it slows down and the refracted ray bends towards the normal.
  • The process of splitting white light into its constituent colors is termed as dispersion.
  • The bending of light when it passes around an edge or through a small opening is called diffraction.
  • The process of transforming unpolarized light into the polarized light is known as polarization.
  • When two or more light waves having the same frequency and wavelength traveling in the same medium meet together at a point, they cancel or enhance the effect of each other at that point. This phenomenon is called interference of light waves.
  • The property of light travelling in a straight line is known as rectilinear propagation of light.
  • A ray can be defined as an imaginary straight line drawn in the direction in which light travels.
  • A collection of light rays travelling together is known as a light beam.
  • The dark region behind an opaque object where the light cannot reach is known as shadow.
  • The umbra is the innermost and darkest part of a shadow, where the light source is completely blocked by the opaque body.
  • The penumbra is the region in which it gets light from some parts of the source of light.
  • The antumbra is the lighter area of a shadow that appears beyond the umbra, at a certain distance from the object casting the shadow..
  • Solar eclipse happens when the Sun, Moon and Earth are perfectly aligned, and the moon comes between the earth and the sun during their motion. In this case the Moon blocks light from the Sun and casts a shadow on Earth.
  • The Lunar Eclipse occurs when the Earth, the Sun and the Moon come in a straight line, and the Earth come in-between the Sun and the Moon.
  • A pinhole camera is a simple camera without a lens but with a hole of pin size.
  • The image formed by a Pinhole Camera is real, smaller than the object, and inverted.
  • In a pinhole camera

  • Regular reflection is reflection from smooth and shiny surfaces.
  • Diffuse reflection is reflection from rough, unpolished surface.
  • The law of reflection is stated as follows:
  • The incident ray, the reflected ray and the normal to the surface lie in the same plane.
  • The angle of incidence is equal to the angle of reflection, i.e., i = r.
  • The image formed by a plane mirror is virtual, erect, the same size as that of the object, laterally inverted and is formed behind the mirror as the object is in front of it.
  • A spherical mirror of which the reflecting surface is curved inwards is known to be concave mirror.
  • A spherical mirror having its reflecting surface curved outwards is known to be convex mirror.
  • Depending on the position of the object, concave mirror can produce an image of any characteristics (real or virtual, magnified or diminished)
  • Independent of the position of the object, the nature of the image formed by a convex mirror is always, virtual, erect and diminished.
  • The Mirror Equation:

  • Magnification(m)

  • The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation.
  • The seven members of electromagnetic family are: radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays and gamma-rays.
  • Laser is an acronym for “Light Amplification by Stimulated Emission of Radiation”, which produces a light of a certain wavelength only.
  • Photoelectric effect is the process of emitting the electrons from the surface of a metal when the metal surface is exposed to an electromagnetic radiation of sufficiently high frequency.
  • The electrons emitted in this process are known as photoelectrons and the current constituted by these electrons is known as photoelectric current.
  • Einstein’s Photoelectric Equation: Ephoton = Φ + Eelectron ⇒ hf = hfth + ½mev2
  • The minimum amount of energy required to remove an electron from the metal is called the threshold energy or work function.
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