100 Most Important MCQ Of Illumination with answer & explanation

Answer.4. 100 per second

Explanation:-

Light flicker is a phenomenon of rapid, quick, and repeated changes in the brightness of light over time.  The lamps normally flicker at twice the line frequency. An incandescent bulb on an alternating current circuit experiences a heat/cool cycle at twice the current frequency and they get brighter & dimmer., in relation to the peaks and zero-crossings of current. On 50 Hz AC power, that will be 100 times per second. 

Answer.1. Candle power of the source

Explanation:-

According to the cosine emission law or Lambert’s emission law.

Illumination (E) = I.Cos³θ/r²

Where

I = luminous Intensity

r = radius

Law of illumination

Suppose a point source of light is illuminating a surface. Then illuminance (or illumination) E of the surface depends upon the following factors:

 E is directly proportional to the luminous intensity (I) i.e candela power of tile source

i.e. E  ∝ I

E is inversely proportional to the square of the distance (r) of the surface from the source

i.e. E ∝ r²

E is directly proportional to the cosine of the angle (θ) made by the normal to tile illuminated surface with the direction of  the incident flux i.e.

i.e. E  ∝ Cosθ

The appearance of an illuminated surface depends on how light is reflected from the surface. If the surface is diffuse (rough), the reflected light will depend only on the illumination arriving directly from the light sources in the scene. Alternatively, if the surface is specular (smooth), the reflected light will depend on the illumination arriving directly from the light sources and on the indirect illumination arriving on this surface after having been reflected off other surfaces in the scene or been transmitted through the surface (if it is transparent). 

Answer.4. 5500 A

Explanation:-

The wavelength of the green color is in the range of 4950 – 5700 A°. 

The eye is most sensitive for a wavelength of 5,500 A°.  So that, the relative sensitivity according to this wavelength is taken as unity. 

Answer.4. 1/d²

Explanation:-

According to the cosine emission law or Lambert’s emission law.

Illumination (E) = I.Cos³θ/d²

Where

I = luminous Intensity

d = radius

Law of illumination

Suppose a point source of light is illuminating a surface. Then illuminance (or illumination) E of the surface depends upon the following factors:

 E is directly proportional to the luminous intensity (I) i.e candela power of tile source

i.e. E  ∝ I

E is inversely proportional to the square of the distance (d) of the surface from the source

i.e. E ∝ 1/d²

E is directly proportional to the cosine of the angle (θ) made by the normal to tile illuminated surface with the direction of  the incident flux i.e.

i.e. E  ∝ Cosθ

Answer.3. 10^-8 cm

Explanation:-

One angstrom is equal to 10^-8 cm and  0.1 nm

Answer.1. Zinc silicate

Explanation:-

The most common fluorescent substances are silicates and sulfides, with calcium tungstate for photographic work. Al excellent zinc silicate occurs naturally in the mineral willemite but all other substances are prepared artificially.

The light emitted by the zinc silicate-coated fluorescent screen of the cathode ray tube is usually of green color.

White fluorescence can be obtained by mixing cadmium sulfide and Zinc cadmium sulfide in suitable proportion.

Answer.1. Yellow

Explanation:-

Light consists of colors of varying wavelengths. Visible light ranges from red, with a wavelength of about 7,000-angstrom units, down to violet, with a wavelength of about 4,000 angstroms. 

RED: 7000 A (angstrom) = (7000 nanometers)

ORANGE: 5890 A (angstrom) = (589 nanometers)

YELLOW: 5510 A (angstrom) = (551 nanometers)

GREEN: 5120 A (angstrom) = (512 nanometers)

BLUE: 4750 A (angstrom) = (475 nanometers)

INDIGO: 4490 A (angstrom) = (449 nanometers)

VIOLET: 4000 A (angstrom) = (400 nanometers)

Hence Yellow color has the wavelength between green and orange color.

Answer.3. Sodium

Explanation:-

Working of Sodium Vapor Lamp

Initially, the sodium is in the form of a solid, deposited on the walls of the inner tube. When sufficient voltage is impressed across the electrodes, the discharge starts in the inert gas, i.e., neon; it operates as a low-pressure neon lamp with pink color.  At the time of start, the neon gas vaporizes and develops sufficient heat to vaporize metallic sodium in the U-shaped tube. The temperature of the lamp increases gradually and the metallic sodium vaporizes and then ionizes thereby producing the monochromatic yellow light. This lamp takes 10-15 min to give its full light output. The yellowish output of the lamp makes the object appears gray.

In order to start the lamp, 380-450 V of striking voltage is required for 40- and 100-W lamps. These voltages can be obtained from a high reactance transformer or an autotransformer. The operating power factor of the lamp is very poor so a capacitor is placed to improve the power factor to above 0.8. More care should be taken while replacing the inner tube, if it is broken, then sodium comes in contact with the moisture; therefore, fire will result. The lamp must be operated horizontally or nearly so, to spread out the sodium well along the tube.

Answer.1. 5500 A°

Explanation:-

Relative sensitivity: The reacting power of the human eye to the light waves of different wavelengths varies from person to person, and also varies with age. 

The eye is most sensitive for a wavelength of 5,500 A° So that, the relative sensitivity according to this wavelength is taken as unity.

Answer.1. Magnesium-white

Explanation:-

Neon lights are a type of cold cathode gas-discharge light. The color of the light depends on the gas in the tube. Neon lights were named for neon, a noble gas that gives off a popular orange light, but other gases and chemicals are used to produce other colors, such as hydrogen (red), helium (yellow), carbon dioxide (white), and mercury (blue).

Magnesium vapor in the filament lamp gives the green light.