Class X- Physics- Light and Reflection

Hope all of you enjoyed your Holidays. But now its time to get back on the road of studies. So here are 7 Questions on the topic "Light: Reflection and Refraction". So enjoy.............

Questions

1.   Define Principal Focus of a Concave mirror.

2.   A spherical mirror and a thin spherical lens have each focal length of -15 cm. Which kind of lens and mirror these are?

3.   A ray of light passing through the centre of curvature goes back on the same path. Why?

4.   What is the nature of image formed by a concave mirror if magnification produced by the mirror is +3?

5.   Write two differences between real and virtual images.

6.   Define power of a lens and write its SI unit.

7.   What is the refractive index of water and air?

Answers

1. The Principal focus of a concave mirror is a point on its principal axis to which all the light rays which are parallel and close to the axis, converge after refection from the concave mirror.

2. Mirror= Concave Mirror
    Lens= Concave Lens

3. If a ray of light is passing through the centre of curvature then this means that the ray is incident normally (or perpendicular) on the mirror. This means that the angle of incidence as well as the angle of reflection is 0. Since the angle of reflection is 0 the ray will come back in the same path.

4. Virtual and Erect

5. (I) Virtual images are represented by dotted lines in the ray diagram but real images are represented by solid bold lines.

(ii) Virtual images cannot be projected on a screen but real images can be projected on a screen
{ANY TWO}

6. The power of a lens is the measure of the degree of convergence or divergence of light rays falling on it.

Its SI unit is dioptre.

7. 1.33 and 1.0003 respectively