light 10 Flashcards
What enables us to see objects?
An object reflects light that falls on it. This reflected light, when received by our eyes, enables us to see things.
What are the two laws of reflection of light?
(i) The angle of incidence is equal to the angle of reflection, and (ii) The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.
What is a concave mirror?
A spherical mirror whose reflecting surface is curved inwards, that is, faces towards the center of the sphere.
What is a convex mirror?
A spherical mirror whose reflecting surface is curved outwards.
Define the pole of a spherical mirror.
The center of the reflecting surface of a spherical mirror. It lies on the surface of the mirror.
Define the center of curvature of a spherical mirror.
The center of the sphere of which the reflecting surface of a spherical mirror forms a part.
Define the radius of curvature of a spherical mirror.
The radius of the sphere of which the reflecting surface of a spherical mirror forms a part.
Define the principal axis of a spherical mirror.
A straight line passing through the pole and the center of curvature of a spherical mirror.
What is the relationship between the radius of curvature (R) and focal length (f) of a spherical mirror?
R = 2f
List uses of concave mirrors.
Concave mirrors are commonly used in torches, search-lights and vehicle headlights to get powerful parallel beams of light. They are often used as shaving mirrors to see a larger image of the face. Dentists use concave mirrors to see large images of the teeth of patients. Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.
List a use of convex mirrors.
Convex mirrors are commonly used as rear-view (wing) mirrors in vehicles.
Why are convex mirrors preferred for rear-view mirrors in vehicles?
They always give an erect, though diminished, image and they have a wider field of view as they are curved outwards.
State the mirror formula.
1/v + 1/u = 1/f, where v is the image distance, u is the object distance, and f is the focal length.
What is magnification?
Magnification is the ratio of the height of the image to the height of the object. It can be expressed as: m = h’/h, where h’ is the height of the image and h is the height of the object.
How is magnification related to object distance (u) and image distance (v)?
m = -v/u
What is refraction of light?
When traveling obliquely from one medium to another, the direction of propagation of light in the second medium changes.
What are the laws of refraction of light?
(i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane. (ii) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given color and for the given pair of media.
State Snell’s law of refraction.
sin(i) / sin(r) = constant, where i is the angle of incidence and r is the angle of refraction.
Define refractive index.
The refractive index of the second medium with respect to the first is the ratio of the speed of light in medium 1 to the speed of light in medium 2.
Define absolute refractive index.
If medium 1 is vacuum or air, then the refractive index of medium 2 is considered with respect to vacuum, and it is called the absolute refractive index of the medium.
What is a lens?
A transparent material bound by two surfaces, of which one or both surfaces are spherical.
What is a convex lens?
A lens that is thicker at the middle as compared to the edges and converges light rays. It is also called a converging lens.
What is a concave lens?
A lens that is thicker at the edges than at the middle and diverges light rays. It is also called a diverging lens.
Define the optical center of a lens.
The central point of a lens. A ray of light through the optical center of a lens passes without suffering any deviation.
