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# Mirrors

When you look in the mirror have you noticed something interesting about you and the image of you in the mirror? Let us carry out a small activity. Stand in front of the mirror and move your right hand. Now lift your left hand. Did you notice that in the mirror the right appears left and vice versa? To understand this let us talk about Mirrors.

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Laws of Reflection
Reflection through Spherical Mirror
Application of Lenses

## Mirrors

A smooth and highly polished reflecting surface are is a mirror. Most commonly used are plane mirrors.

### Lateral Inversions in Plane Mirrors

The word ‘AMBULANCE’ is opposite because when the driver of the vehicle ahead of the ambulance looks in her/his mirror, the person can read it as ‘AMBULANCE’ and give way to it.

### Spherical Mirrors

Suppose you are sitting at the dining table and you don’t like the food, you start playing with the spoon. You look yourself in the spoon and you notice that you look pretty funny. The moment you get the spoon closer you get a magnified image and when taken far, you see an inverted image. Do you know what’s really happening? To understand what is happening lets us talk about the special class of mirrors known as spherical mirrors.

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Let us first understand the terms of spherical mirrors.

• Radius of Curvature (c): It is the distance between Pole and the Center of curvature.
• Center of Curvature (r):  The Center of Curvature of a spherical mirror is the point in the center of the mirror which passes through the curve of the mirror and has the same tangent and curvature at that point.
• Aperture: It is a point from which the reflection of light actually happens.
• Pole (p): Pole is the midpoint of a mirror. It’s twice the focus.
• Focus: It is any point, where light rays parallel to the principal axis, will converge after reflecting from the mirror.
• Principal axis: An imaginary line passing through the optical center and the center of curvature of the spherical mirror.
• Focal Length: It is on the axis of a mirror where rays of light are parallel to the axis converge after reflection or refraction.

#### Spherical mirrors are of two types:

• Convex Mirror
• Concave Mirror

### Concave Mirror

We are familiar that the spherical mirrors are not plane, they are curved in one particular direction. They are curved inward.  A concave mirror is also known as the converging mirror as in these type of mirrors light rays converge at a point after they strike and are getting reflecting back from the reflecting surface of the mirror.

A concave mirror produces real and inverted images except when the object is placed very near to the mirror that pole (p) and the focus (f) where the image produced is virtual and erect. The concave mirror is used in shaving mirrors to see a large image of the face. It is also useful in vehicle headlights and torches. Dentists also use a concave mirror to get the bigger image of the teeth.

#### Convex mirror

The convex mirror has a reflective surface that curves outward. These mirrors are “always” form virtual, erect and diminished regardless of the distance between the object and mirror.

When parallel rays of light strike the mirror, they are reflected in a way wherein they spread out or diverge. For this reason, a convex mirror is also a diverging mirror too. If these reflected rays are extended behind the mirror by dotted lines, they meet at a point. This point is the focus of the convex mirror. The concave mirror is used in the vehicle so that the driver is aware of the vehicle coming from behind. They are also used in street light reflectors.

## Question For You

Q. The following is used in the rear-view mirrors of vehicles:

1. Plane Mirror
2. Convex Mirror
3. Convex Lens
4. Any of these

Answer: B. The Convex Mirror is used in the rear-view mirrors of vehicles as it forms upright/erect images and has a wider field of view.

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