Lamp & Bulb topic plays a crucial role in electrical engineering exams and is a commonly asked topic in competitive exams like SSC JE, RRB JE, UPPCL JE, and other Junior Engineer exams. Understanding different types of lamps, their working principles, luminous efficacy, and related terms is essential for aspirants. In this post, we have compiled important MCQs on lighting and lamps along with correct answers and short explanations to help you in quick revision and exam preparation.
1. Which gas is commonly filled in incandescent bulbs to prevent filament oxidation?
A) Oxygen
B) Nitrogen
C) Argon
D) Carbon dioxide
Answer: C) Argon
Explanation: Argon is an inert gas that prevents oxidation and reduces the evaporation of the tungsten filament, thereby increasing the lifespan of the bulb.
2. What is the typical power factor of an incandescent lamp?
A) 0.5 lagging
B) 0.8 lagging
C) Unity
D) 0.85 leading
Answer: C) Unity
Explanation: Incandescent lamps are resistive loads with no inductance or capacitance, so their power factor is unity (1.0).
3. Which lamp has the highest luminous efficacy?
A) Incandescent lamp
B) Fluorescent lamp
C) LED lamp
D) Halogen lamp
Answer: C) LED lamp
Explanation: LED lamps convert most of the electrical energy into visible light, offering the highest luminous efficacy among all lamp types.
4. In a fluorescent lamp, the starter is used to:
A) Increase brightness
B) Reduce flickering
C) Initiate the arc
D) Stabilize voltage
Answer: C) Initiate the arc
Explanation: The starter preheats the electrodes and helps establish an arc between them to start the lamp.
5. The color rendering index (CRI) of a lamp indicates:
A) Energy efficiency
B) Color temperature
C) Ability to reproduce colors accurately
D) Luminous flux
Answer: C) Ability to reproduce colors accurately
Explanation: CRI measures how accurately a light source displays colors in comparison to natural light.
6. Which lamp operates on the principle of electric discharge through mercury vapor?
A) Incandescent lamp
B) Halogen lamp
C) Mercury vapor lamp
D) LED lamp
Answer: C) Mercury vapor lamp
Explanation: Mercury vapor lamps produce light by passing an electric discharge through mercury vapor inside the lamp.
7. The unit of luminous flux is:
A) Candela
B) Lumen
C) Lux
D) Watt
Answer: B) Lumen
Explanation: Lumen is the SI unit used to measure the total amount of visible light emitted by a source.
8. Which of the following lamps requires a ballast for operation?
A) Incandescent lamp
B) LED lamp
C) Fluorescent lamp
D) Halogen lamp
Answer: C) Fluorescent lamp
Explanation: A fluorescent lamp needs a ballast to control the starting and operating current of the lamp.
9. The luminous efficacy of a lamp is defined as:
A) Luminous flux per unit area
B) Luminous flux per unit power consumed
C) Power consumed per unit luminous flux
D) Illuminance per unit area
Answer: B) Luminous flux per unit power consumed
Explanation: Luminous efficacy measures how efficiently a lamp converts electrical energy into visible light (lumens per watt).
10. Which lamp is most suitable for street lighting due to its high luminous efficacy?
A) Incandescent lamp
B) Sodium vapor lamp
C) Halogen lamp
D) Fluorescent lamp
Answer: B) Sodium vapor lamp
Explanation: Sodium vapor lamps are highly efficient and provide bright light, making them ideal for street lighting.
11. The phenomenon where a rotating object appears stationary under certain lighting is called:
A) Stroboscopic effect
B) Flicker
C) Glare
D) Persistence of vision
Answer: A) Stroboscopic effect
Explanation: Under certain lighting frequencies, rotating or moving objects may appear stationary due to the stroboscopic effect.
12. Which lamp has the shortest lifespan?
A) LED lamp
B) Fluorescent lamp
C) Incandescent lamp
D) Sodium vapor lamp
Answer: C) Incandescent lamp
Explanation: Incandescent lamps typically have the shortest lifespan, usually around 1000 hours, due to filament degradation.
13. The color temperature of a lamp is measured in:
A) Kelvin
B) Celsius
C) Lumens
D) Candela
Answer: A) Kelvin
Explanation: Color temperature describes the hue of light emitted and is measured in Kelvin (K), ranging from warm to cool tones.
14. Which of the following is a cold cathode lamp?
A) Neon lamp
B) Fluorescent lamp
C) Mercury vapor lamp
D) Halogen lamp
Answer: A) Neon lamp
Explanation: Neon lamps are cold cathode discharge lamps that operate without heating the cathode to emit electrons.
15. In a lighting circuit using filament lamps, a 1% voltage drop results in approximately:
A) 1% decrease in light output
B) 3% decrease in light output
C) 10% decrease in light output
D) No change in light output
Answer: C) 10% decrease in light output
Explanation: Incandescent lamps are sensitive to voltage changes; even a 1% voltage drop can reduce light output by about 10%.
16. Which lamp uses a tungsten filament enclosed in a quartz envelope filled with halogen gas?
A) Incandescent lamp
B) Halogen lamp
C) Fluorescent lamp
D) Sodium vapor lamp
Answer: B) Halogen lamp
Explanation: Halogen lamps use tungsten filaments and halogen gas to recycle evaporated tungsten, enhancing efficiency and life.
17. The function of a choke in a fluorescent lamp is to:
A) Stabilize current
B) Provide high voltage for starting
C) Reduce flickering
D) Improve power factor
Answer: B) Provide high voltage for starting
Explanation: The choke, or ballast, generates a high voltage spike to initiate the arc in a fluorescent lamp.
18. Which lamp type is known for its instant start and high efficiency?
A) Incandescent lamp
B) Fluorescent lamp
C) LED lamp
D) Mercury vapor lamp
Answer: C) LED lamp
Explanation: LED lamps light up instantly and offer excellent energy efficiency, making them suitable for modern lighting needs.
19. The unit of illuminance is:
A) Lumen
B) Candela
C) Lux
D) Watt
Answer: C) Lux
Explanation: Illuminance refers to the amount of light falling on a surface and is measured in lux (lumens per square meter).
20. Which lamp has the highest initial cost but offers long-term energy savings?
A) Incandescent lamp
B) Halogen lamp
C) LED lamp
D) Fluorescent lamp
Answer: C) LED lamp
Explanation: LED lamps cost more initially but provide significant long-term savings due to lower energy consumption and longer life.