Test: Class 10 General Science NCERT Based - 3 - UPSC MCQ

1. Image formed by a plane mirror is always virtual and erect.

2. The size of the image is equal to that of the object.

3. The image formed is as far behind the mirror as the object is in front of it.

4. The image formed is laterally inverted.

• A transparent material bound by two surfaces, of which one or both surfaces are spherical, forms a lens. This means that a lens is bound by at least one spherical surface. In such lenses, the other surface would be plane. A lens may have two spherical surfaces, bulging outwards. Such a lens is called a double convex lens. It is simply called a convex lens. It is thicker at the middle as compared to the edges.

• Similarly, a double concave lens is bounded by two spherical surfaces, curved inwards. It is thicker at the edges than at the middle. A double concave lens is simply called a concave lens.A lens, either a convex lens or a concave lens, has two spherical surfaces. Each of these surfaces forms a part of a sphere.

• Concave mirrors are commonly used in torches, searchlights and vehicles headlights to get powerful parallel beams of light as these mirrors possess the ability to focus parallel rays of light to a point, produce a large size image.

• They are often used as shaving mirrors to see a larger image of the face The dentists use concave mirrors to see large images of the teeth of patients.Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

• Light enters the eye, through a thin membrane called cornea. Cornea forms a transparent bulge on the front surface of the eyeball.

• Pupil is a pigmented layer of tissues that makes up the colored portion of the eye. Its primary function is to control the amount of light entering in the eye.

• The eye lens forms an inverted real image of the object on the retina. The retina is a delicate membrane having an enormous number of light-sensitive cells.

Myopia is caused by two reasons:

1. Excessive curvature of eye lens.

2. Elongation of eyeball. A person with this defect has the far point nearer than infinity. Such a person may see clearly upto a distance of a few metres.In a myopic eye, the image of a distant object is formed in front of the retina and not at the retina itself.

• Hypermetropia is also known as farsightedness. A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly. The near point, for the person, is farther away from the normal near point (25 cm).

• Such a person has to keep a reading material much beyond 25 cm from the eye for comfortable reading. This is because the light rays from a closeby object are focussed at a point behind the retina.

• This defect can be corrected by using a convex lens of appropriate power. Eye-glasses with converging lenses provide the additional focussing power required for forming the image on the retina.

• The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly 6 × 10¹⁸ electrons.

• The electric current is expressed by a unit called ampere (A). One ampere is constituted by the flow of one coulomb of charge in a second, that is, 1 A = 1 C/1 s. An instrument called ammeter measures electric current in a circuit. To measure the current in a circuit, it is connected in series in a circuit.