Light: Reflection and Refraction Flashcards
What is a lens?
A transparent material bound by two surfaces, of which one or both surfaces are spherical, forms a lens.
What is a convex lens and concave lens?
A lens that has two spherical surfaces, bulging outwards is known as double convex lens or convex lens.
A lens that has two spherical surfaces, curved inwards is known as double concave lens or concave lens.
Nature of convex and concave lens
Convex lens converges light rays hence are also called converging lens.
Concave lens diverge light rays and are also called diverging lens.
Give examples of lenses used in daily life
The glasses used is spectacles and that by a watchmaker are examples of lenses.
What is optical centre?
The central point of a lens is its optical centre. It is represented by the letter O
* a ray of light through the optical centre of a lens passes without suffering any deviation
What is principal axis of lens
An imaginary straight line passing through the two centres of curvature of a lens is called its principal axis
What is aperture of lens?
The effective diameter of the circular outline of a spherical lens is called its aperture
What are thin lenses with small aperture?
Lenses whose aperture is much less than its radius of curvature and two centres of curvatures are equidistant from the optical centre O such lenses a court in lenses with smaller apertures
The paper begins to burn producing a smoke. It may even catch fire after a while why does this happen?
OR
How can we obtain a real image of Sun? (Illustrate the activity as well)
The light from the sun constitutes parallel rays of light. These rays were converged by the lens at the sharp bright spot formed on the paper. In fact, the bright spot you got on the paper is a real image of the sun. The concentration of the sunlight at a point generated heat. This caused the paper to burn.
Principal focus of convex lens
Several rays of light parallel to the principal axis are falling on a convex lens. These rays after refraction from the lens are converging to a point on the principal axis. This point on the principal axis is called the principal focus of the lens.
Principal focus of concave lens
Several rays of light parallel to the principal axis are falling on a concave lens. These rays after refraction from the lens are appearing to diverge from a point on the principal axis. This point on the principal axis is called the principal focus of the concave lens.
What is the nature of image formed by concave lens?
A concave lens will always give a virtual, erect and diminished image irrespective of the position of the object
Name the factor on which the ability of a lens to converge or diverge the light rays depends?
Focal length of lens
How does a convex lens of short focal length bent the light rage?
A convex lens of short focal length, bends the light rays through large angles by focusing them closer to the optical centre
What causes higher divergence in a concave lens?
A concave lens of very short focal length causes higher divergence than the ones with longer focal length
What makes things visible?
Light. An object reflects light that falls on it, this reflected light, when received by our eyes, enables us to see things.
During the day, sunlight helps us to see objects
What is diffraction of light?
If an opaque object on the path of light becomes very small, light has a tendency to bend around it and not walk in a straight line. This effect is known as diffraction of light.
In this phenomenon light is thought of as a wave.
How does light travel?
By observing the common optical phenomena around us, we may conclude that light travels in straight lines.
Ray of light
A small source of light casting a sharp shadow of an opaque object indicates a ray of light
Are the laws of reflection applicable for all types of mirror?
The laws of reflection are applicable to all types of reflecting surfaces including spherical surfaces.
What are spherical mirrors?
Mirrors, whose reflecting surfaces are spherical, are called spherical mirrors. The reflecting surface of such mirrors can be considered to form a part of the surface of a sphere.
What is pole of the mirror?
The centre of the reflecting surface of a spherical mirror is a point called the pole. It lies on the surface of the mirror. Represented by letter P.
What is centre of curvature of spherical mirror?
The reflecting surface of a spherical mirror forms a part of a sphere. This sphere has a centre. This point is called the centre of curvature of the spherical mirror. It is represented by the C. The centre of curvature is not a part of the mirror. It lies outside its reflecting surface .
What is radius of curvature of the mirror?
The radius of the sphere of which the reflecting surface of a spherical mirror forms a part, is called the radius of curvature of the mirror. Represented by letter R
Principal axis
An imaginary straight line passing through the pole and the centre of curvature of a spherical mirror. Principal axis is normal to the mirror at its pole.
The paper at first begins to burn producing smoke. Eventually, it may even catch fire. Why does it burn?
The light from the sun is converged at a point as a sharp bright spot by the mirror. In fact, this spot of light is the image of the sun on the sheet of paper. This point is the focus of the concave mirror. The heat produced due to the concentration of sunlight ignites the paper.
What is focal length?
The distance between the pole and the principal focus of a spherical mirror is called the focal length and it is represented by the letter f.
What is aperture of mirror?
The diameter of the reflecting surface of a spherical mirror is called its aperture.
Where does the principal focus of spherical mirror lie?
The principal focus of a spherical mirror lies midway between the pole and centre of curvature
How is the image of sun?
Real, inverted, tiny image.
Define principal focus of concave and convex mirror.
The principal focus of a concave mirror is a point on the principal axis of the mirror, at which rays of light incident on the mirror in a direction parallel to the principal axis, actually meet after reflection from the mirror.
The principal focus of a convex mirror is a point on the principal axis of the mirror from which rays of light incident on the mirror in a direction parallel to the principal axis appear to diverge after reflection from the mirror
Which mirror is used to view full length images of large objects?
Convexed mirror. One such mirror is fitted in the wall of Agra Fort facing Taj Mahal.
What is object distance and image distance?
The distance of the object from its pole is called object distance (u).
The distance of the image from the pole of the mirror is called the image distance (v).
