The chapter on light reflection and refraction is assigned a weightage of \(7\ or\ 8\ marks\), highlighting its significance in the overall curriculum. Understanding this chapter will enhance to know behaviour of light and using ray diagrams to illustrate concepts and explain real-life applications of optics.
Also to prepare effectively for related exam questions. It is essential to grasp the concepts of reflection & refraction and image formation by mirrors. Focusing on these concepts will greatly benefit both academic performance and practical application in physics.
In the below, we have provided the details of the question distribution among the different sections.
- Section A (\(1 \)mark) - One question
- Section B (\(2\) mark) - One question
- Section D or E (4 or 5 mark) - One question
Learning outcomes:
- Introduction to light: Understanding the nature and properties of light.
- Laws of reflection and refraction: Applying the laws of reflection and refraction to practical situations.
- Analyzing image formation in mirrors using ray diagrams: Outline the rule of image formation by spherical mirrors in order to complete the ray diagrams by drawing reflected rays.
Light appears to travel in straight-lines when we observe common optical phenomena around us. The fact that a small light source casts a sharp shadow on an opaque object indicates that light travels in a straight line, commonly referred to as a ray of light.
The majority of the light falling on a highly polished surface, such as a mirror, is reflected. The reflected ray obeys the laws of reflection.
The laws of reflection:
(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.
A spherical mirror's reflecting surface can be curved inwards or outwards.
concave mirror - reflecting surface that is curved inwards.
convex mirror - curved reflecting surface that faces outwards.
Terms related to spherical mirrors:
Terms related to spherical mirror
PYQ:
The radius of curvature of small aperture spherical mirrors is found to be equal to twice the focal length, \(R\ =\ 2f\).
This indicates that the principal focus of a spherical mirror lies midway between the pole and centre of curvature.
Image formation by concave mirror:
Image formation by convex mirror:
Sign convention:
The mirror formula, which is expressed as shows a relationship between these three quantities.
\(\frac{1}{f}\ =\ \frac{1}{u}\ +\ \frac{1}{v}\)
The magnification can be related to object distance (u) and the image distance (v).
\(m\ =\ \frac{-v}{u}\)
(or)
\(m\ =\ \frac{h'}{h_o}\) =\( \frac{-v}{u} \)
The presence of a negative sign in the magnification value indicates that the image is real.
The presence of a positive sign in the magnification value indicates that the image is virtual.
\(m\ <\ 1\) − The image formed is enlarged.
\(m\ <\ 1\) − The image formed is diminished.
PYQ:
Exam tip:
1. Type of mirror
2. Sign concention
3. Unit conversion
4. Magnification