Which one of the following does not convert electrical energy into light energy?
- A.A candle
- B.A light-emitting diode
- C.A laser
- D.A television set
Correct answer
Explanation
The correct answer is A, A candle. A candle gives light by burning wax, so it converts chemical energy, not electrical energy, into light and heat.
In a burning candle the wax vapour combines with oxygen in the air; the chemical energy stored in the wax is released as heat and light. No electric current is involved at any stage. The other three devices all run on electricity: their circuits use electrical energy to produce light. Energy is never created or destroyed but only changes form, which is the law of conservation of energy.
B is wrong: a light-emitting diode is a semiconductor device that gives out light when an electric current passes through it.
C is wrong: a laser is powered electrically and turns that energy into a narrow, intense beam of light.
D is wrong: a television set uses electrical energy to light up its screen and also produces sound.
Exam tip: candle and torch flame = chemical → light and heat; LED, laser, bulb and TV = electrical → light; solar cell = light → electrical.
Practice Questions
View allSolanum tuberosum is the scientific name of which vegetable?
- A.Tomato
- B.Brinjal
- C.Potato
- D.Onion
Show answer
The potato is Solanum tuberosum, and the epithet tuberosum points to the tuber, a swollen underground stem rather than a root, which is the part eaten; the plant belongs to the nightshade family and reached India through the Portuguese.
Read the full explanation →What is the scientific name of the lotus, the national flower of India?
- A.Rosa indica
- B.Nelumbo nucifera
- C.Jasminum officinale
- D.Helianthus annuus
Show answer
The lotus, declared the national flower of India, is Nelumbo nucifera, an aquatic plant rooted in the mud of ponds and tanks with leaves and flowers held above the water, and it carries a long place in Indian art and religion.
Read the full explanation →What is the scientific name of turmeric?
- A.Curcuma longa
- B.Piper nigrum
- C.Zingiber officinale
- D.Allium sativum
Show answer
Turmeric is Curcuma longa, a rhizome of the ginger family whose yellow colour comes from curcumin, and it is well known in the intellectual property story in which a United States patent on the use of turmeric for wound healing was revoked after India produced evidence of traditional knowledge.
Read the full explanation →Bombyx mori is the scientific name of which organism?
- A.Honeybee
- B.Earthworm
- C.Silkworm
- D.Housefly
Show answer
Bombyx mori is the mulberry silkworm, the insect reared in sericulture, whose larva spins the cocoon from which mulberry silk is reeled, and the word mori refers to the mulberry on whose leaves it feeds.
Read the full explanation →What is the scientific name of neem?
- A.Ocimum sanctum
- B.Azadirachta indica
- C.Ficus religiosa
- D.Santalum album
Show answer
Neem is Azadirachta indica, a tree valued in Indian medicine for its leaves, bark and oil, and it is remembered in current affairs as well because a European patent on a neem based fungicide was revoked after India challenged it.
Read the full explanation →