A mirror is a polished surface that reflects images or a mirror is something that reflects or gives likeness. We have basically two types of mirrors;

5. Plane mirrors and
5. Curved mirrors.

1. PLANE MIRRORS

A plane mirror is a mirror with a flat rather than curved surface. When light strikes a plane mirror, it is regularly reflected.

Laws of Reflection

• The angle of incidence is always equal to the angle of reflection. I.e. i=r.
• The incident ray, the reflected ray and the normal all lie on the same plane at the point of incidence.

Types of Reflection

Basically, we have two types of reflection, namely;

• Regular reflection and
• Irregular reflection.

1. Regular reflection

It occurs when light strikes a smooth surface or when light strikes a regular surface.

1. Irregular Reflection

Properties of Image Formed on a Plane Mirror

• Image is same size as object.

• Image is far behind the mirror as object is far in front.

• Image is virtual, that is no light is collected o reaches the image.

• Image is laterally inverted. That is, if the object’s right hand is up, the image’s left hand will be up.

INCLINED MIRRORS

These are mirrors which are placed at angle teta (θ) with their reflective surface facing each other.

Number of images produced= 360θ

Number of images seen= 360θ-1

Example: Two plain mirrors are placed at an angle of 90° and an object is placed between them. Calculate:

1. Number of images produced.
2. Number of images seen.

Solution

1. Number of images produced=360θ But θ=90°;

Number of images= 36090=4 images Produced

2. Number of images seen=36090-1=3 images seen.

Exercises

• 5kg of water at 80°C is poured into 2kg of water at 20°C. Given that the specific heat capacity of water is 4200J/kgK. Calculate the equilibrium temperature of the mixture.
• The specific heat capacity of mercury is 150J/kgK. What is the meaning of this?
• 50kg of an object falls from a height of 70m and the temperature change was 20K. Calculate the specific heat capacity of the object.
• An electric kettle is rated 2000W. Supply heat energy to 5kg of water and the temperature rise from 20°C to 60°C. Calculate how long it takes for the temperature to change.