A (a)   is an optical instrument that forms and records an image of an object.

In a digital camera, the electronic sensor stores the image (a)   .

The lens used in a camera is a (a)   lens.

When taking a photograph in bright light a (a)   f-number (narrow aperture) must be used.

When taking a photograph in bright light a (a)   aperture must be used.

When taking a photograph in dim light a (a)   f-number must be used.

When taking a photograph in dim light a (a)   aperture must be used.

The (a)   controls the time during which light enters the camera through the lens.

The shutter speed is expressed in terms of the (a)   time.

The shorter the exposure time, the (a)   the shutter speed is.

The film is actually a (a)   which receives the image.

The (a)   in the camera is a screen which receives the image.

The film consists of a thin layer of chemical compounds of (a)   .

(a)   reaction occurs when light energy falls on the film.

In a (a)   camera, the film is replaced by an electronic sensor.

The electronic image sensor is made up of millions of tiny (a)   which response to light.

Human eye consists of (a)   organs.

(a)   eye is capable of receiving visual images.

The human eye is very similar to a (a)   in many aspects.

The eyelid is similar to the (a)   of the camera.

The front portion of the eye is covered by a tough, transparent membrane called the (a)   .

The liquid between the cornea and the eyelens is called (a)   humor.

The liquid between the eyelens and the retina is the (a)   humour.

The (a)   is the colored portion of the eye.

The (a)   controls the amount of light energy entering the eye.

The (a)   is in the centre of the iris and the light passes through it.

The pupil is similar to the (a)   in the camera.

The (a)   adjusts the size of the pupil in the eye.

The pupil automatically dilates in (a)   light.

The pupil automatically contracts in (a)   light.

When (a)   objects are viewed, the ciliary muscles permit the eyelens to form a more convex shape.

When near objects are viewed, the ciliary muscles contract and permit the eyelens to form a (a)   convex shape.

When distant objects are viewed, the ciliary muscles (a)   .

When distant objects are viewed, the eyelens becomes (a)   convex.

When near objects are viewed, the ciliary muscles (a)   .

When (a)   objects are viewed, the ciliary muscles relax.

When (a)   objects are viewed, the ciliary muscles make the eyelens to have greater power.

When (a)   objects are viewed, the ciliary muscles make the eyelens to have less power.

The ciliary muscles of the eye are generally similar to the (a)   of the camera.

The (a)   is the light sensitive area of the cells, at the back of the eye.

The retina consists of rods and (a)   .

The (a)   spot is the most light-sensitive spot on the retina.

The (a)   spot is the zero light-sensitive spot on the retina.

The (a)   spot on the retina is used for viewing very small objects.

The yellow spot on the retina consists of (a)   exclusively.

The (a)   spot on the retina of the eye has no rods or cones.

When an image is formed at the (a)   spot of the retina, it cannot be seen at all.

The optic nerve enters the eye at the (a)   spot.

The light energy falling on the retina is transmitted to the (a)   by means of the optic nerve.

Farsightedness is also known as (a)   .

Nearsightedness is also known as (a)   .

The least distance of distinct vision for normal vision is (a)   .

People with normal vision can see clearly objects which are at (a)   .

The maximum distance of distinct vision for normal vision is (a)   .

A common type of microscope is a (a)   microscope.

A compound microscope has at least two (a)   lenses.

In a compound microscope, the lens nearer to the object is called the (a)   .

In a compound microscope, the lens through which the final image is viewed is called the (a)   .

The image formed by the objective of the compound microscope must be between the focal length of the (a)   .

The final image formed by the compound microscope can be seen clearly when the eye is very close to the (a)   .

Compound microscopes have the magnifying power of several (a)   .

The optical microscopes have a maximum magnifying power of about (a)   .

The electron microscopes have a maximum magnifying power of about (a)   .

The (a)   microscopes use optical lenses

The (a)   microscopes use electrostatic or electromagnetic lenses.

In an optical microscope, (a)   is used as a source of illumination.

In an electron microscope, a beam of accelerated (a)   is used as a source of illumination.

Electron microscope uses the (a)   beam to illuminate the specimen and create an image.

In electron microscope, the accelerated electron beam is focused by (a)   lenses.

Galileo invented a (a)   astronomical telescope.

The refracting astronomical telescope consists of two (a)   lenses.

To obtain the sharp images of distant objects by the refracting astronomical telescope, the (a)   should have a large diameter.

The objective of the reflecting astronomical telescope is a (a)   .

Most telescopes used at the astronomical observatories in the world are (a)   telescopes.

The eyepiece of the reflecting astronomical telescope is a (a)   lens.

In the terrestrial telescope, the objective is a (a)   lens.

In the terrestrial telescope, the eyepiece is a (a)   lens.

(a)   prisms are used in binoculars.

A (a)   is an optical instrument which consists of a pair of telescopes one for each eye.

Binoculars are widely used as (a)   telescopes.

Because of the successive total internal reflections in the prisms, the length of the (a)   telescope is greatly reduced

Optics is the branch of physics that studies the nature and properties of (a)   .

Mirrors are optical instruments employing the (a)   of light.

Lenses are optical instruments employing the (a)   of light.

(a)   produces stimulated emission of photons from excited atoms or molecules.

The laser medium (gain medium) is the (a)   emitting the laser beam.

The process of supplying energy to the laser medium is known as (a)  

The optical cavity or the (a)   concentrates the light to stimulate the emission of laser radiation.

The optical cavity of the laser system consists of (a)   highly reflective mirrors.

The (a)   with reflectivity of almost 100 % completely reflects the light.

The reflectivity of perfect reflector is (a)   %.

In stimulated emission, the transition occurs when the atom in its excited state interacts with an incident photon at the transition (a)   .

Atoms undergoing stimulated emission radiate photons of the same frequency in the same direction and in phase with the stimulating (a)   .

For stimulated emission to occur, a (a)   inversion would be needed.

For stimulated emission to occur, the population of the upper level of a transition would have to be (a)   than that of the lower level.

A typical laser beam divergence is around a (a)   .

Laser beam will spread only to 1 m in diameter after travelling (a)   .

Laser range finders are used to determine the (a)   to an object.

The inner layer of the optical fibre is called the (a)   .

The outter layer of the optical fibre is called the (a)   .

The (a)   of the optical fibre protects the optical fibre.

For a light ray injected to the optical fibre, the angle of incidence at the core-cladding interface must be greater than the (a)   .

The (a)   is used to examine the interior of a hollow organ or cavity of the human body.

Endoscopes use (a)   to observe an image inside the body.

The shortest wavelength of light the human eye can response is (a)   .

The longest wavelength of light the human eye can response is (a)   .

Human eye is more sensitive to (a)   light of 555 nm compared to other colors.

In photometry, there are (a)   main photometric quantities.

The unit of luminous flux is the (a)   .

One lumen (1 lm) is equivalent to 1/683 watt of light with a wavelength of (a)   .

Luminous intensity is measured in (a)   .

The (a)   is the SI basic unit of luminous intensity.

In SI system, a solid angle is expressed in (a)   .

The solid angle subtended at the centre by the whole surface area of the sphere is (a)   .

The SI unit for illuminance is (a)   .

The unit 1 lx is equivalent to (a)   .

The minimum average illuminance should be (a)   with a high uniformity and low glare.

The (a)   controls the amount of light energy entering the eye.

For farsightedness, the rays from near objects intersect at a point (a)   the retina.

Nearsightedness can be corrected by the use of spectacles with (a)   lens.

(a)   microscopes use electrostatic or electromagnetic lenses.

An optical instrument used for viewing distant objects is called a (a)   .

A (a)   consists of a pair of telescopes employing the total reflecting prisms.

The optical cavity consists of two highly reflective (a)   .