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NCERT Solutions for Class 5th The World Around Us Chapter 7 Understanding How Fuel Works — Activity 4

Book page 120 Updated on2026-09-19

Q1.
Understanding How Fuel Works — 1. Place two diyas (lamps) on a flat surface. 2. In Diya 1 — place a cotton wick without any oil, and in Diya 2 — place a cotton wick and pour some oil around it. 3. Light the wicks in both the diyas under adult supervision. 4. Observe what happens to the diyas.
Answer

What you will see: both wicks catch fire at first. Diya 1, with no oil, burns for only a few seconds — the dry cotton itself burns up, turns black and the flame dies. Diya 2, with oil, keeps burning with a steady yellow flame for a long time, and its wick does not get used up.

How to do it (with an adult beside you):

  1. Put two clay diyas side by side on a plate or a stone floor, away from paper and cloth.
  2. Roll two wicks of the same size from clean cotton. Put one in each diya.
  3. Leave Diya 1 dry. Pour a spoon of oil into Diya 2 so the wick soaks in it. Wait a minute for the oil to climb up the wick.
  4. An adult lights both wicks at the same moment.
  5. Watch both flames. Count slowly, or look at a clock.
Diya 1 — no oil flame dies in seconds small, short flame Diya 2 — with oil burns steadily, for long tall, steady flame Oil
Same wick, same flame at the start — only one of them has a fuel supply.
What I watchedDiya 1 (no oil)Diya 2 (with oil)
Does it light?YesYes
Size of the flameSmall and weakTall and steady
How long it burnsA few seconds onlyMany minutes, until the oil runs out
The wick afterwardsBurnt black and crumblyStill there, just charred at the tip
Safety first: Do this only with an adult. Tie back long hair, roll up loose sleeves, keep a mug of water nearby, and put the diyas on a stone or metal plate — never on paper or cloth.
Q2.
(a) Which diya burns longer? Why?
Answer

Diya 2 — the one with oil — burns much longer. It burns longer because it has a fuel to keep the flame going. Diya 1 has no fuel, so its flame dies as soon as the dry cotton itself is burnt up.

What is happening inside Diya 2, step by step:

  1. The bottom of the wick sits in the oil.
  2. The cotton wick slowly draws the oil up along its threads, the way a cloth soaks up water.
  3. At the top, the heat of the flame turns that oil into a vapour.
  4. The vapour burns, and that burning is the flame you see.
  5. As soon as a little oil is used, more oil climbs up the wick to take its place.
  6. So the flame is fed again and again — and it keeps burning until the diya is empty.
Diya 1: dry wick → wick itself burns → flame goes out in seconds
Diya 2: oil climbs the wick → oil burns → more oil comes up → flame keeps burning
The idea to carry away: A flame does not live on its own. It must be fed. Whatever we feed it — oil, gas, wood, coal, petrol — is called a fuel. No fuel, no flame.
Q3.
(b) What is acting as a fuel here?
Answer

The oil is the fuel. That is exactly what the book says on the next page: “The oil is the fuel.”

Do not get confused by the wick. The wick is only the pipe that carries the oil to the flame. It is not the fuel itself — which is why the wick is still there after the diya has burned for a long time, but the oil is gone.

PartIts job
Clay diyaHolds the oil safely
Cotton wickCarries the oil up to the flame, drop by drop
OilThe FUEL — it burns and gives the light and heat
AirFuel needs air to burn; cover the flame and it goes out
Where else you meet fuel: The chapter lists them — we use different fuels in daily life for cooking, for lighting diyas and for running vehicles. Cooking gas in the stove, wood in the chulha, petrol in the scooter, diesel in the tractor and oil in the diya are all fuels. Each one is a store of energy waiting to be released by burning.
Try it: Light Diya 2 and then place a glass tumbler upside down over it. The flame grows dim and goes out, even though there is plenty of oil left. Fuel alone is not enough — burning also needs air.
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