Question

(a) Name the lens which produces an erect and diminished image always? (b) Which mirror is used as a rear view mirror in a vehicle? (c) Define one dioptre. (d) The size of the object is given as $2cm$. The magnification due to the mirror will be $+1$ . Then calculate the size of the image? (e) When a light ray is passing through a denser medium to a rarer medium, which angle will be greater? Angle of incidence or angle of refraction?

Answer 1

The erect and diminished one are the characteristics of the virtual image. A rear view mirror is used in a vehicle in order to get a complete view of the things behind. Dioptre is the unit of optical power. The magnification produced will be the ratio of the size of the image to the size of the object. Angle of incidence is the angle between the normal and the incident light. And the angle of refraction is the angle between the normal and refracted light.

Complete answer:
(a) a concave lens is the lens which always gives a virtual, erect and diminished image. This is true at any position of the object. Therefore the question is answered.

(b) The convex mirrors are generally used as the rear view mirrors. It will enable the driver to view a much wider area than a plane mirror. The images created will be erect and also their size will be diminished than the object. Therefore, it is used as a rear view mirror in vehicles in order to see objects at the backside of the vehicle.

(c) A dioptre is a unit of measurement for the optical power of a spherical lens or a curved mirror. This can be equal to the reciprocal of the focal length which is to be in metres. It is abbreviated as D.

(d) The size of the object is given as,
${{h}_{o}}=2cm$
The magnification produced is given as,
$m=+1$
The magnification produced will be the ratio of the size of the image to the size of the object. That is,
$m=\dfrac{{{h}_{i}}}{{{h}_{o}}}$
Therefore, the size of the image will be obtained by rearranging the equation,
$m{{h}_{o}}={{h}_{i}}$
Substituting the values in the equation will give,

& +1\times 2={{h}_{i}} \\\ & {{h}_{i}}=2cm \\\ \end{aligned}$$ Hence the answer is calculated. (e) When a ray of light passes from a denser to rarer medium, as the light ray bends away from the normal, the angle of refraction would be greater than angle of incidence.  **Note:** Rear view mirrors are having an anti-glare function. They are commonly known as a “day-night” mirror. At night, the headlights behind reflect off the mirror and will distract glare by flipping the lever varying the angle. This will help the rear mirrored surface to reflect the headlights up and out of your eyes.