Science [2 Mark Questions]

The image is real, inverted and magnified. It is formed beyond the centre of curvature of the mirror.

A ray of light passing through the centre of curvature of a concave mirror is reflected back along the same path because it strikes the concave mirror at right angles to its surface due to which the angle of incidence and angle of reflection both are 0°.

Virtual and erect.

Formation of image by a convex mirror when the object is at infinity palced any where between the pole of mirror the pole of mirror and infinity.

Formation of image by a convex mirror when the object is at infinity (Iarge distance).

Uses of Plane mirrors:

1. Plane mirrors are used to see ourselves. The mirrors on our dressing table and in bathrooms are plane mirrors.
2. Plane mirrors are fitted at blind turns of some busy roads so that drivers can see the vehicles coming from the other side and prevent accidents.
3. Plane mirrors are used to make periscopes.
4. Plane mirrors are fixed on the inside walls of certain shops to make them look bigger.

The image will form 2m behind the mirror and the width of the image of boy’s mouth will be 5cm.

A driver prefers to use a convex mirror as a rear-view mirror because:

1. A convex mirror always produces an erect image of the objects.
2. A convex mirror has wider field of view.

Concave mirrors are used as shaving mirrors. This is because when the face is placed close to a concave mirror (so that the face is within its focus) the concave mirror produces a magnified and erect image of the face. Since a large image of the face is seen in the concave mirror, it becomes easier to make a smooth shave.

1. If m = +4, then the image is virtual and erect.
2. If m = +4, then the image is real and inverted.

When the object is at a considerable distance (or at infinity) from a concave mirror, then its image is formed at the focus. This fact can be used to find out the focal length of a concave mirror quickly but approximately.We focus a distant object (several metres away) like a window or tree on a screen by using a concave mirror whose focal length is to be determined. The sharp image of window or tree will be formed at the focus of the concave mirror. That is, the distance of image (or screen) from the concave mirror will be equal to the focal length of concave mirror. This distance can be measured with a scale. It will give us the approximate focal length of the concave mirror.

A image of our face in a plane mirror is laterally inverted, so left is right and right is left. However, in a photograph of our face this is not the case. A mirror surface is smooth, so the reflection by a mirror is a regular reflection. A parallel beam of light incident on it, gets scattered by making reflected rays in different directions.

Real image can be obtained on a screen because light rays actually pass through a real image but virtual image cannot be formed on screen because light rays do not actually pass through a virtual image.
Example:
The image formed on a cinema screen is an example of real image.
The image formed by a plane mirror is a virtual image.

When an object is placed at the centre of curvature (C) of a concave mirror, the image formed is:

1. At the centre of curvature (C).
2. Real and inverted.
3. Of same size as the object.

1.  

2. Lateral inversion.

Two uses of convex mirror:

1. A convex mirror is used as a rear-view mirror in vehicles because it forms erect and dimished images of the objects and has a wider field of view.
2. Big convex mirrors are used as security mirror in shops so that a large number of goods displayed in the shop can be seen in the convex mirror.

1. Mirror B is convex, as it forms a small image.
2. Mirror A is concave, as it forms a large image.

A wall has a rough surface, so the reflection by a wall is a diffuse reflection. A parallel beam of light incident on it is reflected in different directions.

All the light rays which are parallel to the principal axis of a concave mirror, converge at the the principal focus (F) after reflection from the mirror. Since a concave mirror converges a parallel beam of light rays, it is also called a converging mirror.

When an object is placed beyond the centre of curvature (C) of a concave mirror, the image is:

1. Between the focus and centre of curvature.
2. Real and inverted.
3. Smaller than the object (or diminished).

Coming soon

Concave mirror is used in a solar furnace. The solar furnace is placed at the focus of a large concave reflector. When parallel rays of light from the sun fall on the surface of the concave mirror, rays gets reflected and meet at the focus of the mirror due to the converging nature of concave mirror. Thus, the furnace kept at the focus becomes very hot. Even steel can be melted in this furnace.

Concave mirror is used in the headlights of a car. This is because when a lighted bulb is placed at the focus of a concave mirror reflector, then the diverging light rays of the bulb are collected by the concave reflector and then reflected to produce a strong, parallel-sided beam of light (which travels a considerable distance in the darkness of night).

1. Principal focus of a concave mirror: 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 reflection from the concave mirror.
2. Focal length of a concave mirror: The focal length of a concave mirror is the distance between its pole and the principal focus.

A communications satellite sends a parallel beam of signals down to the Earth. If these signals are to be focussed onto a small receiving aerial, then the best shape of the metal dish that can be used to collect them would be concave. The metal dish will behave like a concave mirror, which is a converging mirror.

Two types of spherical mirrors are:

1. Concave mirror.
2. Convex mirror.

Type of mirror represented by the:

1. Back side of a shining steel spoon – convex mirror.
2. Front side of a shining steel spoon – concave mirror.

When the boy walks towards the mirror at a speed of 1m/ s, his image will also appear to move towards the mirror at the same speed of 1m/ s. So, the speed at which his image approach him will be 2m/ s + 2m/ s = 4m/ s.

1. Principal focus of a convex mirror: The principal focus of a convex mirror is a point on its principal axis from which a beam of light rays, initially parallel to the axis, appears to diverge after being reflected from the convex mirror.
2. Focal length of a concave mirror: The focal length of a convex mirror is the distance from the pole (P) to its principal focus (F).

We cannot use a concave mirror as a rear-view mirror in vehicles because a concave mirror produces inverted images of distant objects. So, all the vehicles will be seen running upside down in the mirror.

Because while driving our car. if we see in our rear-view mirror that the hospital van is coming from behind, then we get the laterally inverted image ofand read its as AMBULANCE and give way for it to pass throught.

Concave mirror is used by dentists. The dentist holds a small concave mirror in such a way that the tooth lies within its focus. A magnified image of the tooth is then seen by the dentist in the concave mirror. Since the tooth looks much bigger, it becomes easy to examine the defect in the tooth.

We can distinguish between a plane mirror, a concave mirror and a convex mirror by bringing our face close to each mirror, turn by turn. If the image is of the same size as our face, it is a plane mirror. If the image is magnified, it is a concave mirror. If the image is diminished, it is a convex mirror.

Place a plane mirror in front of the message and see the image of the message. The mirror now reads as 'meet me at midnight'. The phenomenon of lateral inversion is used here.

For obtaining an enlarged upright image of an object, the object is placed between focus (F).

1. Image will form between pole and focus.

2. At focus.

If the object is moved further away from the mirror, the image is formed nearer to the mirror and the size goes on decreasing.

All the light rays which are parallel to the principal axis of a convex mirror, appear to diverge from the principal focus (F) after reflection from the mirror. Since a convex mirror diverges a parallel beam of light rays, it is also called a diverging mirror.

The focal length of the mirror is PF = 10cm.The object is placed at B such that PB = 8cm. This means that the object lies between the pole and focus of the concave mirror. The image formed is virtual, erect and magnified.