Class 7 Unit-7 (Energy in Daily Life)

 

Unit-7 (Energy in Daily Life)

Introduction

Energy is the capacity of doing work. There are different forms of energy.

 

Renewable and non-renewable sources of energy

1. Nonrenewable sources of energy

-Non-renewable resources are the energy that can be used only once and cannot be made again quickly.
-Once they are finished, they take millions of years to form again.

-Energy obtained from non-renewable sources is called non-renewable energy.

-For example: Natural gas, petroleum, coal, nuclear energy.

 

2. Renewable sources of energy 

-Renewable natural resources are the energy that can be

  used again and again. They do not run out easily

  because nature replaces them in a short time.

-Energy obtained from non-renewable sources is called

  renewable energy.

-For example: Solar energy, wind energy,

  hydroelectricity,  geothermal energy, wood, biomass.

 

Fossil Fuels
Fossil fuels are energy sources formed from the remains of plants and animals that lived millions of years ago. They are found deep inside the Earth. The main types of fossil fuels are coal, oil (petroleum), and natural gas.

Uses of Fossil Fuels:

• They provide energy for electricity generation.
• Used as fuel for vehicles (petrol, diesel, and gas).
• Used in factories to produce heat and energy.
• Used in making plastics, fertilizers, and chemicals.

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Advantages of Fossil Fuels

1. High Energy Content: Fossil fuels provide a lot of energy when burned.
2. Easy to Use: They are easy to transport, store, and use.
3. Reliable Source: They can provide continuous and stable energy.
4. Supports Industry: Fossil fuels are important for industries and transportation.

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Disadvantages of Fossil Fuels

1. Non-renewable: They take millions of years to form, so they will run out one day.
2. Pollution: Burning fossil fuels releases smoke and harmful gases, causing air pollution.
3. Global Warming: Gases like carbon dioxide contribute to climate change.
4. Health Hazards: Pollution from fossil fuels can cause respiratory problems.
5. Environmental Damage: Mining and drilling can destroy forests and habitats.

 

Alternative Energy

Alternative energy is energy that comes from renewable sources instead of fossil fuels. These

Types of Alternative Energy:

1. Solar Energy – Energy from the sun.
2. Wind Energy – Energy from moving air (wind).
3. Hydropower – Energy from flowing water.
4. Biomass Energy – Energy from plants, crops, and organic waste.
5. Geothermal Energy – Energy from heat inside the Earth.

 

Ways of saving energy

1.      Use of solar energy and reduce the use of non-renewable energy.

2.      Stop to use unnecessary utilization of energy.

3.      Encourage the people for the use of biomass energy and other renewable sources of energy.

4.      Utilization of electrical devices at households and industries.

 

Heat

-Heat is a form of energy that transfers from one body to another. It gives us the sensation of warmth.

-Heat is measured by a device called calorimeter.

-The SI unit of heat is Joule (J). Heat is also measured in calorie unit.

 

Temperature

-The measurement of hotness or coldness of a substance is known as its temperature.

-Temperature is measured by a device called thermometer.

-The SI unit of temperature is Kelvin (K).

-We often use two units of temperature, degree Celsius (⁰C) and degree Fahrenheit (⁰F)

 

1. Digital Thermometer

A digital thermometer is an electronic device that shows temperature on a digital display.
Uses:

• Measures body temperature quickly and accurately.
• Can also measure the temperature of liquids or the environment.
  Advantages:
• Fast reading in a few seconds.
• Easy to read.
• No mercury, so it is safe.

 

2. Clinical Thermometer

A clinical thermometer is a thermometer used to measure human body temperature.
Features:

• Usually contains mercury or alcohol.
• Shows temperatures from about 35°C to 42°C.
• Measures body temperature to check for fever.
• Accurate for human body temperature

 

3. Laboratory Thermometer

A laboratory thermometer is used in labs to measure the temperature of liquids, solids, or gases.
Features:

• Wider scale than clinical thermometer.
• Can measure a large range of temperatures.
• Made of glass with mercury or colored alcohol.
• Measuring temperature in experiments.
• Monitoring chemical reactions.

Wave

A wave is a repeated disturbance that moves through a medium (like air, water, or a solid) and transfers energy from one place to another without moving the matter itself.

Types of Waves:

1. Mechanical Waves

o Need a medium (like air, water, or solid) to travel.

o Example: Sound waves, water waves, and waves on a string.

2. Electromagnetic Waves

o Do not need a medium; they can travel through empty space.

o Example: Light waves, radio waves, and X-rays.

3. Transverse Waves

o The particles of the medium move perpendicular to the direction of wave motion.

o Example: Light waves, waves on a string.

4. Longitudinal Waves

o The particles of the medium move in the same direction as the wave.

o Example: Sound waves, compressions in a spring.

 

 

Light

Light is a form of energy that helps us see objects.

 

Reflection of light

Reflection of light is the bouncing back of light rays when they strike a smooth and shiny surface like a mirror.

Types of Reflection:

1. Regular Reflection (Specular Reflection):
• Occurs on smooth surfaces like mirrors or calm water.
• Produces a clear image.

 

1. Regular Reflection

Regular reflection occurs when light rays fall on a smooth and shiny surface and bounce back in the same direction.

Characteristics:

• Produces a clear and sharp image.

• Reflection from a plane mirror.
• Reflection from calm water or a polished metal surface.

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2. Irregular Reflection

Irregular reflection occurs when light rays fall on a rough surface and scatter in many directions.

Characteristics:

• Does not produce a clear image.

• Reflection from a wall, paper, etc.

• Helps us see objects around us because light scatters in all directions.

 

 

Luminous objects produce light themselves (like the Sun or a bulb).

Non-luminous objects do not produce light but can reflect light (like the Moon or a mirror).

 

Laws of Reflection:

1. The incident ray, reflected ray, and normal all lie in the same plane.
2. The angle of incidence (i) is equal to the angle of reflection (r).

 

Uses of Reflection of Light:

• Mirrors in homes, vehicles, and telescopes.
• Periscopes in submarines.
• Cameras and optical instruments.
• Helps in seeing objects around corners using reflected light.

 

Periscope
A periscope is an instrument that allows a person to see objects that are not in the direct line of sight, usually above, around, or behind an obstacle.

Uses of Periscope:

1. Submarines: To see above the water surface while staying underwater.
2. Armies: To look over walls or obstacles safely.
3. Tanks and vehicles: To see outside without exposing the driver.
4. Science experiments: To study reflection of light.