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Class 8 Dynamics of Population: cheat sheet
CBSE Social Science. How population is measured and changes: the census, birth and death rates, fertility and the replacement level, sex ratio, ageing and the demographic dividend.
Key ideas
- Demography is the study of population and how it changes; India counts its people in a census every 10 years.
- The birth rate is live births per 1,000 people in a year.
- A fertility rate of 2.1 children per woman is the replacement level; long below it, a population stops growing and may shrink.
- Sex ratio is the number of females per 1,000 males.
- Life expectancy is the average number of years a newborn is expected to live.
- A demographic dividend is the gain a country can make when many people are young and of working age.
- Japan’s population is ageing because few children are born and people live long.
- People migrate to cities for jobs, education and health care.
Remember
| Replacement level | 2.1 children per woman |
| Sex ratio of 943 | 943 females per 1,000 males |
| India’s population | about 361 million (1951) to about 1,210 million (2011) |
| Most populous country | India, since 2023 |
| India’s median age | about 28 (Japan about 50) |
| Life expectancy | about 30 at Independence, about 70 in 2024 |
| China’s One-Child Policy | 1979 to 2015 |
Watch out
- Reading sex ratio per 100 or per 1,000 people: it is females per 1,000 males.
- Thinking a fertility rate of 2 keeps a population steady: replacement level is 2.1.
- Mixing up the birth rate (per 1,000 people) and the fertility rate (per woman).
Worked example
India became the most populous country in 2023, and China’s One-Child Policy ended in 2015. How many years before 2052 was each?
Working: 2052 − 2023; 2052 − 2015
Answer: 29 years; 37 years
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