Science [2 Mark Questions]

Both, convex lens and concave mirror, converge parallel rays of light coming from infinity (parallel to the principal axis) at the focus.

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

The image formation by a concave mirror when an object is placed between focus and centre of curvature of the mirror at centre of curvature of the mirror.

1. The object should be placed at 20cm because a convex mirror forms a real, magnified image when an object is placed between f and 2f.
2. The object should be placed at 10cm because a convex mirror forms a virtual, magnified image when an object is placed placed between f(focus) and the optic centre
3. The object should be placed at 35cm because a convex mirror forms a real, diminished image when an object is placed beyond 2f.
4. The object should be placed at 30cm because a convex mirror forms a real image of the same size when an object is placed at 2f.

The light ray bends towards the normal. When a ray of light travels from an optically rarer medium to an optically denser medium, it gets bent towards the normal. Since water is optically denser than air, a ray of light travelling from air into the water will bend towards the normal.

It is unwise to look at the sun because the convex lens focusses a lot of sun rays into our eyes and this may damage them.

The change in direction of light when it passes from one medium to another obliquely, is called refraction of light.

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).

Converx lens having 4cm focal length-because it will produce greatest magnification.

Factors on which the lateral displacement depends are:

1. Angle of incidence.
2. Thickness of glass slab.
3. Refractive index of glass slab.

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.

Convex mirror is used.

Concave mirrors are used in headlights of car. The position of the is placed nearer to the focus of the concave. The reason is that the main purpose of the head lights is to focus or show the light for larger area as much as possible and to send a beam of light infront of the car. Because light from a source comes in all directions (diffration) and in case of head lights we don't want to face the light towards us. And we want to change the direction of those rays which are coming to us to travel along the road. This problem is solved by placing light source or bulb at the focus of the concave mirror because the light rays coming from focus towards the mirror after reflection goes parallel to principal axis or along the road.

1. Ray of light travelling from air into an optically denser medium.

2. Ray of light travelling from an optically denser medium into air.

Concave mirror is used.

A virtual magnified image is the one which cannot be taken on a screen and whose size is larger than that of the object.

When a beam of light rays enters the glass block, it gets refracted. It bends towards the normal. Also, when these light rays leave the block, they bend away from the normal.

When light rays fall normally on the surface of the glass block, there is no bending of rays; the rays travel straight.

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

When the object is placed between optical centre and the focus of the convex lens a virtual and enlarged image is formed.

A ray of light passing through the centre of curvature of a concave mirror retraces its path (gets reflected along the same path), because as the ray of light passes through centre of curvature of a concave mirror it strikes the mirror along the normal i.e. it incidences on to the mirror at 90 degree. Hence the incident ray coincides with the normal.
Therefore angle of incidence = 0 so, as we know according to law of reflection.
angle of reflection = 0, hence the angle of reflection too become zero degree, thus ray of light retraces its path.

When the fork is seen through lens A, it appears to be diminished. Such diminished object is observed when it is placed near a concave lens. Therefore, lens A is concave, i.e., diverging in nature. When the fork is seen through lens B, it appears to be enlarged. Such enlarged image is formed by a convex lens when an object is placed between the lens and its focus. Therefore, lens B is a convex, i.e., converging in nature.

1. To produce a large amount of bending, the light ray has to enter the glass with a large angle of incidence.
2. For no refraction, the light ray has to enter the glass perpendicularly.

1. Aperture means diameter of concave mirror of a spherical mirror.
2. Radius of curvature is radius of sphere whose mirror forms a part.

The real, inverted and highly magnified image forms at infinity on the other side of the object when the object is placed at the focus of the lens.

When an object is placed beyond 2f in front of a convex lens, then the image formed is between f and 2f on the other side of the lens, it is real, inverted and smaller than the object.

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.

1. Beyond 2F.
2. At 2F.
3. Between F and 2F.
4. Between F and optical centre.

We know that pencil appears to be bent at the interface of air and water because of refraction of light. The degree of refraction depends on refractive index of a given liquid. Refractive indices of kerosene, water and other liquids would be different. Hence, degree of bend would be different in case of different liquids.

It means that both the object and the image formed by a spherical mirror (concave or convex) are erect (I.e., upright). An erect image is always virtual. Thus, positive magnification indicates that the image formed by a spherical mirror is virtual.
Linear magnification (m): Linear magnification produced by a mirror is the ratio of the size of the image formed (denoted by h') to the ratio of the size of the object.

In case of reflection, the angle of reflection is equal to the angle of incidence. On the other hand, in case of refraction, the angle of refraction is not equal to the angle of incidence.

1. Convex lens (since image is real, inverted and diminished).
2. Concave lens (since image is virtual, erect and diminished).