Science [1 Mark Questions]

diagram 47.

1. Positive power: Convex lens.
2. Negative power: Concave lens.

Lateral inversion.

When the object is placed at centre of the curvature of the concave mirror, the object and its image coincides.

Refraction of light.

Object should be placed at a distance less than focal length.

A convex mirror or diverging mirror is a curved mirror in which the reflective surface bulges towards the light source. Convex mirrors reflect light out wards, therefore they are not used to focus light.

This is due to refraction of light.

When this point light source is placed at the focus of convex lens then after falling on convex lens it will become parallel to the principal axis.

At the centre of curvature.

Glass has higher refractive index.

Refraction of light.

To find the focal length of the concave mirror, use a similar procedure as you did with the convex lens. Arrange your mirror, meter stick, and screen. Point the mirror at distant (greater than 10m) object and move the screen along the meter stick until you obtain a sharp image of the distant object on the screen. The distance between the mirror and the screen is the approximate focal length of the mirror.

Focal length of a lens depends on the refractive index of the glass from which it is made, and on the curvature of its two surfaces.

At infinity.

Concave lens.

Convex mirror.

Refractive index has no units.

According to the second law of reflection, angle of incidence is equal to the angle of reflection.
Given angle of incidence = 30°
Therefore, angle of reflection = 30°
Angle made by the reflected ray with mirror surface = 90° - 30° = 60°

If lens is cut along Perpendicular to principal axis then focal length will be twice the original one.

1. 0°
2. 0°

Convex mirror always produces a virtual, erect and diminished image.

Centre of curvature: Centre of curvature of a spherical mirror is the centre of the hollow sphere of glass of which the mirror is a part.

All the distances are measured from the Pole of a spherical mirror.

Angle to the mirror surface = 40°Therefore, angle of incidence = 90° - 40° = 50°
According to the second law of reflection, angle of incidence is equal to the angle of reflection.
Therefore, angle of reflection = 50°

Pole: The centre of a spherical mirror is called its pole.

The focal length of plane mirrors is considered to be infinite, as the radius of curvature is infinite.

Radius of curvature: Radius of curvature of a spherical mirror is the radius of the hollow sphere of glass of which the mirror is a part.

The image is formed behind the mirror at the same distance as the object is kept in front of the mirror.
Given distance between object and mirror = 10cm.
Distance between mirror and image = 10cm.
Therefore, the distance between object and image = 10 + 10 = 20cm.

The image will be real and inverted, since the magnification has negative value.

Angle of refraction is less than the angle of incidence.

The range of the object distance when placed in front of the mirror is from 0 to 12cm i.e. when object is placed between pole and focus of the mirror. The nature of the Image formed will be magnified, i.e., larger than the size of the object.

One dioptre of is defined as the power of lens having a focal length of 1 m.

The images formed in the convex rear-view mirror will be smaller than those formed in the plane rear-view mirror.

Ray of light going towards the focus of a concave lens.

1. Concave lenses.
2. Convex lenses.

Plane mirror.

Virtual and erect; real and inverted.