What is Boyle's Law? | Simple Explanation for Class 7

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What is Boyle's Law (pressure-volume relationship)?

Grade Level:

Class 7

Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics

Definition

What is it?

Boyle's Law tells us how the pressure and volume of a gas are related when its temperature and the amount of gas stay the same. It states that if you increase the pressure on a gas, its volume will decrease, and if you decrease the pressure, its volume will increase. They are inversely proportional.

Simple Example

Quick Example

Imagine you have a deflated football and you start pumping air into it. As you pump more air (increasing pressure inside), the football gets harder and its volume expands. Now, think about pressing down on a bicycle pump with your finger covering the nozzle. As you push the handle down, the air inside gets squeezed into a smaller space (volume decreases), and you feel more resistance (pressure increases).

Worked Example

Step-by-Step

Let's say you have a gas in a syringe. Initially, its volume (V1) is 100 mL and its pressure (P1) is 1 atmosphere (atm).
---1. We want to find the new volume (V2) if the pressure (P2) is increased to 2 atm, keeping the temperature constant.
---2. Boyle's Law formula is P1 * V1 = P2 * V2.
---3. Substitute the known values: 1 atm * 100 mL = 2 atm * V2.
---4. To find V2, rearrange the equation: V2 = (1 atm * 100 mL) / 2 atm.
---5. Calculate the result: V2 = 100 / 2 mL.
---6. V2 = 50 mL.
So, the new volume of the gas will be 50 mL.

Why It Matters

Boyle's Law is crucial in designing everything from scuba diving equipment to space suits, ensuring divers and astronauts can breathe safely at different pressures. It's also vital in medical devices like ventilators and even in understanding how engines work in EVs or how air compressors function in factories. Engineers and doctors use this principle daily.

Common Mistakes

MISTAKE: Thinking pressure and volume increase together | CORRECTION: Remember they are inversely related. When one goes up, the other goes down.

MISTAKE: Forgetting to keep temperature constant | CORRECTION: Boyle's Law only applies when the temperature and the amount of gas do not change.

MISTAKE: Using inconsistent units for pressure or volume | CORRECTION: Always ensure both initial and final pressures use the same unit (e.g., atm, Pascal) and both initial and final volumes use the same unit (e.g., mL, Litre).

Practice Questions

Try It Yourself

QUESTION: A gas has a volume of 5 Litres at a pressure of 3 atm. If the pressure is reduced to 1 atm (constant temperature), what will be its new volume? | ANSWER: 15 Litres

QUESTION: A balloon contains 200 mL of air at 760 mmHg pressure. If the volume is compressed to 100 mL, what is the new pressure in mmHg? | ANSWER: 1520 mmHg

QUESTION: You have 400 cm^3 of gas at 2 atm pressure. If you want to reduce its volume to 100 cm^3, what pressure (in atm) would you need to apply? Assume temperature is constant. | ANSWER: 8 atm

MCQ

Quick Quiz

If the pressure on a gas is doubled while keeping the temperature constant, what happens to its volume?

It also doubles

It remains the same

It is halved

It triples

The Correct Answer Is:

According to Boyle's Law, pressure and volume are inversely proportional. So, if pressure is doubled, volume is halved.

Real World Connection

In the Real World

Scuba divers use Boyle's Law every time they go underwater. As they dive deeper, the water pressure increases, which means the air in their lungs and BCD (Buoyancy Control Device) gets compressed (volume decreases). When they ascend, the pressure decreases, and the air expands. Understanding this helps them manage their air supply and avoid decompression sickness.

Key Vocabulary

Key Terms

PRESSURE: The force applied per unit area | VOLUME: The amount of space a substance occupies | INVERSELY PROPORTIONAL: When one quantity increases, the other decreases proportionally | CONSTANT: Staying the same; not changing

What's Next

What to Learn Next

Great job learning about Boyle's Law! Next, you can explore Charles's Law, which explains the relationship between volume and temperature of a gas. It's another exciting piece of the puzzle to understand how gases behave!