Lamps and Bulbs MCQ Quiz - Objective Question with Answer for Lamps and Bulbs - Download Free PDF

Concept:

Metal Halide Lamps require a starting aid to initiate the arc discharge. An inert gas is used to provide an initial conductive path. Among the gases listed, Argon is commonly used because it ionizes easily and supports the initial arc formation without reacting with the lamp materials.

Why Argon?

- Inert and non-reactive
- Low breakdown voltage
- Facilitates easy arc initiation
- Widely used in discharge lamps and fluorescent tubes

Key Points

• High melting point: Tungsten has a very high melting point of about 3422°C (6192°F), which allows it to withstand the high temperatures generated by the electric current flowing through the filament without melting.
• High specific resistance: Tungsten has a high specific resistance, which means it can produce a significant amount of heat when an electric current passes through it, thus emitting light efficiently.
• Durability: The high melting point and specific resistance also contribute to the durability and longevity of the tungsten filament, making it suitable for prolonged use in incandescent bulbs.
• Efficiency: The properties of tungsten make it efficient in converting electrical energy into light energy with minimal loss in the form of heat.

Additional Information

• Incandescent Bulbs:
  • Incandescent bulbs work by passing an electric current through a thin filament, typically made of tungsten.
  • The filament heats up and emits light as a result of the resistance to the electric current.
  • These bulbs are known for their warm light but are less energy-efficient compared to modern alternatives like LED and CFL bulbs.
• Specific Resistance:
  • Also known as resistivity, it is a measure of how strongly a material opposes the flow of electric current.
  • Materials with high specific resistance are good at converting electrical energy into heat, which is crucial for the operation of incandescent bulbs.

Power Factor of an Ordinary Electric Bulb:

• The power factor of a device is defined as the ratio of the real power used by the device to the apparent power flowing into the circuit.
• It indicates how effectively the electrical power is being converted into useful work output.

Concept of Power Factor:

• Power factor (PF) is given by the formula: PF = Real Power (P) / Apparent Power (S).
• It ranges from 0 to 1, where 1 indicates that all the power is effectively utilized.
• A power factor of 1 (unity) means that all the power is being used effectively for work with no reactive power.
• Power factor less than 1 indicates the presence of reactive power which does not contribute to the work output.

Power Factor of an Ordinary Electric Bulb:

• An ordinary electric bulb (incandescent bulb) operates with a purely resistive load.
• For purely resistive loads, the voltage and current waveforms are in phase, meaning there is no phase difference between them.
• In such cases, the power factor is typically close to unity.
• However, due to minor inductive components such as the filament supports or slight imperfections in the manufacturing process, the power factor can be slightly less than unity.

Therefore, the correct answer is that the power factor of an ordinary electric bulb is slightly less than unity.

Utilization factor

The utilization factor is the ratio of the total lumens required to the total lumens emitted.

Given, Room dimensions = 12m × 16m = 192 m2

Illuminance = 100 lm/m2

Total number of lamps = 24

Luminous flux per lamp = 1600 lm

Each lamp emits 1600 lm and there are 24 lamps. The total lumens emitted by all the lamps is given by:

Total lumens emitted = 24 × 1600 = 38400 lm

UF = Total lumens required / Total lumens emitted

\(UF = {19200 \over 38400}=0.5\)

Concept

The power across a resistor is given by:

\(P={V^2\over R}=I^2R=VI\)

where, P = Power

V = Voltage

R = Resistance

I = Current

Calculation

Given, V = 120 volts

I = 6 A 

P = 120 × 6

P = 720 watts

Different light bulbs last for a different time period. Out of the given lamps, incandescent lamps have the shortest life span in working hours.

• Sodium vapor lamps are also commonly used for sporting events, as they have a very high lumen to watt ratio typically of 80–140 lumens/watt.
• This making them a cost-effective choice when certain lux levels must be provided.
• High-pressure sodium lamps also are known as HPS Lamps or HPS lights are widely used in industrial lighting and many public outdoor areas.
• They are commonly used in public parking lots, roadways, and other security areas.

The correct answer is option 1):(Pink)

Concept:

Depending upon the type of phosphor material used in fluorescent tubes,

we get light of different colors as given in the below table.

• The most useful measure of a light source's color characteristics is the colour rendering index (CRI).
• CRI is a measure of a light source's ability to show object colors "realistically" or "naturally" compared to a familiar reference source, either incandescent light or daylight.
• The color rendering index (CRI) is measured as a number between 0 and 100.
• At zero (0), all the colours look the same.
• A CRI of 100 shows the true colors of the object.
• Incandescent and halogen light sources have a CRI of 100.
• Typically, light sources with a CRI of 80 to 90 are regarded as good and those with a CRI of 90+ are excellent.
• Higher the CRI, the better the color rendering capacity.

The fluorescent lamp makes use of the bimetallic strip.

• When we switch ON the supply, full voltage comes across the lamp and as well as across the starter through the ballast.
• At that full voltage first, the glow discharge is established in the starter. This is because the electrodes gap in the neon bulb of the starter is much lesser than that of the fluorescent lamp.
• Then gas inside the starter gets ionized due to this full voltage and heats the bimetallic strip. That causes to bend the bimetallic strip to connect to the fixed contact. Now, current starts flowing through the starter.
• As soon as the current starts flowing through the touched contacts of the neon bulb of the starter, the voltage across the neon bulb gets reduced since the current, causes a voltage drop across the inductor(ballast).
• At reduced or no voltage across the neon bulb of the starter, there will be no more gas discharge taking place and hence the bimetallic strip gets cool and breaks away from the fixed contact.
   

Given that:

Room dimension = 12 m × 16 m

Output of each lamp (I) = 1600 Lumens

Illumination (E) = 100 lm/m²

Now,

Total lumens emitted by lamps (L_T) = Number of lamps × output of each lamp

∴ L_T = 24 × 1600

L_T = 38400 lumens

Lumens received by working area (L_r) = Area of space × illumination

∴ L_r = 12 m × 16 m × 100 lm/m²

L_r = 19200 lumens

Now,

Utilization factor \( = \frac{{{L_r}}}{{{L_T}}}\) 

Where,

L_r = lumen received by working plane

L_T = Lumen emitted by lamps

∴ utilization factor \( = \frac{{19200}}{{38400}}\) 

Utilization factor = 0.5

Concept:

• Luminous flux (ϕ): Luminous flux is the light energy radiated per second from a luminous body in the form of light waves. It is measured in lumen.
• Illumination (I): The luminous flux falling per unit area on a surface is known as illumination and is expressed in Lumen/m².
• Candle power (C.P): The light radiating capacity of a source is called its candle power. The number of lumens given out by a source per unit solid angle in a given direction is called its candle power.
• Solid angle (ω): The angle subtended by the partial surface area of a sphere at its center is called as solid angle. It is measured in steradians and it is equal to the ratio of area of surface to the square of radius of sphere.

C.P = luminous flux /solid angle

Illumination = luminous flux / area

\(C.P = \frac{\phi }{\omega }\)

\(I = \frac{\phi }{A}\)

\(\omega = \frac{A}{{{R^2}}}\)

Where R = distance of the point from the point of source.

In the given problem R= height at which the lamp is suspended.

\(C.P = \phi \times \frac{{{R^2}}}{A}\)

\(C.P = I \times {R^2}\)

\(180 = 80 \times {R^2}\)

\(R = \frac{3}{2} = 1.5\;meters.\)

Concept:

The stroboscopic effect in fluorescent lamp is a phenomenon which causes running or moving equipment to appear stationary or appear to be operating slower than they actually are.

Fluorescent lamps are provided with 50 Hz ac current supply. When operating under this frequency the lamp becomes zero (crosses zero wave) double the supply frequency, i.e, 100 times for 50 Hz frequency per second. Due to the persistence of vision our eyes do not notice those flickering.

However if the light falls on the moving parts due to illusion, they may appear to be either running slow, or in reverse direction or even may appear stationary. This effect is called stroboscopic effect.

This can be prevented by connecting the twin-tube lights in parallel.

Each tube uses a separate choke and a separate starter, and a capacitor is added in series with the second choke, so as to improve the capacitor. We can also avoid the flickering of tube lights.

Explanation:

Incandescent and halogen lights don't have Stroboscopic effect or they have minimal flicker because they are thermal radiators and have a relatively long persistence (due to the thermal capacity of the tungsten filament).

Dry cell

• A dry cell consists of a metal container in which a low moisture electrolyte paste covers the graphite rod or a metal electrode. Generally, the metal container will be zinc whose base acts as a negative electrode (anode) and a carbon road acts as a positive electrode (cathode). It is surrounded by manganese dioxide and low moisture electrolytes like ammonium chloride paste, which will produce a maximum of 1.5V of voltage, and they are not reversible.
• These are popular batteries used nowadays on laptops, iPods, cellphones.
• The electrodes of the cell are made up of lightweight carbon and lithium

Electric Arc Furnace

• In this, an electric arc is produced between the electrodes. This electric arc is used for melting the metal.
• Usually, the carbon and graphite electrodes are used, and they can be selected based on their electrical conductivity, insolubility, chemical inertness, mechanical strength, resistance to thermal shock, etc.
• The carbon electrodes are used with small furnaces for the manufacturing of ferro-alloys, aluminum phosphorous, etc.

GLS lamps

• Normally, inert gases like argon is used to fill GLS lamps.