📖 Chapter 2 of 8 · Green Energy - Basic 2 · Class 7
Chapter 2: Why Is Clean Energy Better for Us?
Quick Recap of Basic 1. This chapter helps you remember what you learnt in Green Energy — Basic 1, and adds a little more.
In this chapter
- Fossil fuels — coal, oil and gas — and why they are a problem.
- Smoke, dirty air and a warming Earth.
- Units of electricity and how to save them.
- Meet Arjun from Delhi and Nandini from Odisha.
The Big Idea
Coal, oil and gas are called fossil fuels. They formed from plants and animals buried deep underground millions of years ago. Burning them makes smoke and a gas called carbon dioxide, which traps heat and warms the Earth. Fossil fuels will also run out one day. Clean energy makes no smoke while it works, and the Sun and wind will not run out.
Did You Know?
Under India’s UJALA scheme, which began in 2015, more than 36 crore LED bulbs were given to families. An LED bulb uses much less electricity than an old-style bulb for the same light.
Story Time — Arjun and the Grey Winter
Arjun, age 10 · New Delhi
Every November, Arjun notices something strange in Delhi. The sky turns grey, the Sun looks pale like a coin, and his Dadaji starts coughing. On some days his school even closes because the air is too dirty to breathe.
One morning his mother showed him an air-quality app on her phone. It said “Very Poor” in red. “Where does all this smoke come from, Maa?” Arjun asked.
“From many places,” she said. “Vehicles that burn petrol and diesel, dust from roads and building work, factories, and fields where crop waste is burnt. Some power plants burn coal too.”
Just then, a green bus glided to the stop. There was no black smoke from its back and hardly any sound. “This is an electric bus,” Maa smiled. “It runs on a big battery. When that battery is charged with electricity from the Sun or wind, the whole ride is clean.”
On the ride to school, Arjun made a plan. “When the air is good, I will cycle to my tuition class. And I will tell Dadaji that clean energy can help him breathe easier.” Maa ruffled his hair. “Small steps from many people make a big change, Arjun.”
Story Time — Nandini, the Unit Detective
Nandini, age 9 · Bhubaneswar, Odisha
Nandini found a paper on the dining table in Bhubaneswar. “Bapa, what are these ‘units’ on the electricity bill?”
Her father explained, “A unit is how we measure electricity. One unit can run a small 10-watt LED bulb for 100 hours! We used 180 units last month, and we pay for each one. More units also mean more fuel burnt at the power plant.”
Nandini put on her detective cap. She walked through the house with a notebook. The TV was sleeping on standby with its red light on. The fan was spinning in an empty room. A tube light was glowing in the afternoon, while bright sunshine waited outside the closed curtains.
She started the “Switch-Off Squad” with her little brother Sibu. Their rules: switch off what you are not using, open the curtains in the day, and replace old bulbs with LEDs.
Next month, the bill showed only 150 units. Bapa gave the squad a high-five. “You saved 30 units! That is less coal burnt and more money for your books.” Nandini grinned. “The cleanest energy is the energy we do not waste!”
Clean or Not Clean?
Energy sources can be sorted into two groups. Look at the picture and read the points below.
- Renewable (clean): Sun, wind, flowing water, and a few more you will meet in Chapter 5. Nature refills them again and again.
- Non-renewable (fossil fuels): coal, oil and natural gas. They took millions of years to form and are being used up quickly.
- Burning fossil fuels makes smoke that harms our lungs and carbon dioxide that warms the Earth.
- A warmer Earth can bring stronger heatwaves, melting glaciers and changes in the monsoon.
- Saving energy is the easiest clean energy of all — every unit saved is a unit that never needs to be made.
My Energy-Saver Promise: I will switch off lights and fans when I leave a room, use daylight, unplug chargers, and walk or cycle for short trips.
Solved Examples
Think first, then read the answer.
1. What are fossil fuels, and why are they called non-renewable?
Show answer
Answer: Coal, oil and gas are fossil fuels. They took millions of years to form, so once we burn them they cannot be refilled in our lifetime.
2. How does burning coal harm the Earth?
Show answer
Answer: It makes smoke that dirties the air we breathe, and carbon dioxide that traps heat and slowly warms the whole planet.
3. For how many hours can a 10-watt LED bulb glow using 1 unit of electricity?
Show answer
Answer: 1 unit = 1,000 watt-hours. So 1,000 ÷ 10 = 100 hours.
4. An old 60-watt bulb and a 9-watt LED each glow for 5 hours. How much energy does the LED save?
Show answer
Answer: Old bulb: 60 × 5 = 300 watt-hours. LED: 9 × 5 = 45 watt-hours. Saving = 300 − 45 = 255 watt-hours.
5. Is clean energy perfectly clean?
Show answer
Answer: Not 100%. Making panels and turbines uses materials and energy, and solar works only when the Sun shines. But over its whole life, it is far cleaner than burning coal.
✎ Now You Try!
A 50-watt fan is left running for 4 extra hours every day. How many watt-hours are wasted in one day? In a week?
Check Your Understanding
A. Fill in the blanks
- Coal, oil and gas are called fuels.
- Burning fossil fuels releases a gas called dioxide.
- Nandini started the “ Squad” with her brother.
- We measure electricity on our bill in .
- The electric bus Arjun rode runs on a big .
B. True or False
- Fossil fuels will never run out. ( ___ )
- An LED bulb uses less electricity than an old bulb. ( ___ )
- Leaving a TV on standby uses a little electricity. ( ___ )
- Saving energy is also a way to protect the Earth. ( ___ )
C. Choose the correct option
- Which is non-renewable? (a) sunlight (b) coal (c) wind
- Delhi’s winter smoke comes from (a) only one place (b) many places (c) the Moon
- One unit runs a 10-watt LED for (a) 10 hours (b) 50 hours (c) 100 hours
D. Answer in two or three sentences
- Why did Nandini’s electricity bill go down?
- Give two reasons why clean energy is better than coal.
- Write any three energy-saving habits you will follow.
Brain Buster
Find your family’s electricity bill. How many units did you use? Can your family save 10 units next month?
Check your understanding
Tap an answer to see if it is correct. This is just for fun — nothing is saved.
1. Which of these is a fossil fuel?
- Sunlight
- Coal
- Wind
Show answer
B. Coal
2. What does burning coal release that warms the Earth?
- Oxygen
- Carbon dioxide
- Water only
Show answer
B. Carbon dioxide
3. For how long can one unit of electricity light a 10-watt LED bulb?
- 10 hours
- 50 hours
- 100 hours
Show answer
C. 100 hours
4. What is the easiest clean energy of all?
- Energy we save and do not waste
- Burning more wood
- Leaving lights on
Show answer
A. Energy we save and do not waste