GED Science: Energy, Heat, and Waves Concepts
Importance ★★★★★ · 35% (estimate)
Overview
This chapter covers energy: its forms, how it changes from one form to another, how heat moves, and how waves carry energy. It is part of the Energy and Related Systems theme on the GED Science test.
Energy is not created or destroyed; it changes form. A raised object has gravitational potential energy, and a moving object has kinetic energy. A battery stores chemical energy that becomes electrical energy and then light and heat in a flashlight. Efficiency is the share of energy that becomes the useful form. Energy sources can be renewable, like sunlight and wind, or nonrenewable, like coal, oil, and natural gas.
Heat flows from hot to cold by conduction (direct contact), convection (moving liquid or gas), and radiation (waves that can cross empty space). Temperature is not the same as heat: more matter needs more heat for the same temperature change. Exothermic reactions release heat, and endothermic reactions absorb it.
Waves are described by frequency and wavelength, and wave speed = frequency × wavelength. The electromagnetic spectrum runs from radio waves (lowest frequency) through visible light to X-rays and gamma rays (highest). Ultraviolet light causes sunburn. Sound is a mechanical wave that needs matter to travel.
Key concepts
Conservation of energy
Energy changes form but the total stays the same. Falling: potential energy → kinetic energy.
Memory tipLost potential energy = gained kinetic energy (no air resistance).
Potential and kinetic energy
Potential energy is stored (for example, PE = mass × g × height). Kinetic energy is energy of motion.
Memory tipHigh up = potential; moving = kinetic.
Heat transfer
Conduction: through contact. Convection: by moving fluid. Radiation: by electromagnetic waves, even through empty space.
Memory tipTouch, flow, or waves.
Exothermic and endothermic
Exothermic reactions release heat (hand warmers). Endothermic reactions absorb heat (cold packs).
Memory tipExo = exit (heat goes out); endo = enter (heat goes in).
Wave speed
Speed = frequency × wavelength.
Memory tip5 Hz × 2 m = 10 m/s.
Electromagnetic spectrum
Low to high frequency: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma ray.
Memory tipHigher frequency means more energy (UV, X-rays, gamma).
Efficiency
Useful energy out ÷ energy in × 100. The rest usually becomes heat.
Memory tipDivide the useful part by the total, then multiply by 100.
Often tested
- A control group (such as an unwrapped can) shows what happens without the factor being tested.
- The best insulator is the material with the smallest temperature drop.
- Wind, sunlight, and moving water are renewable; coal, oil, and natural gas are not.
- Sound cannot travel through empty space; light can.
Easy to confuse: Three ways heat moves
| Type | How it moves | Example |
|---|---|---|
| Conduction | Through direct contact, mainly in solids | Hot soup warming a metal spoon |
| Convection | By moving liquid or gas | Warm air rising from a heater |
| Radiation | By electromagnetic waves, even through space | Sunlight warming Earth |
3 sample questions
Verified practice questions from this unit.
Question 1. A metal spoon is left in a pot of hot soup, and soon the handle feels hot. How did the heat travel up the spoon?
- ① Convection
- ② Evaporation
- ③ Radiation
- ④ Conduction
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Answer: ④ Conduction
Key point: Conduction: heat moves through direct contact
In conduction, heat passes from particle to particle through direct contact. Metals are good conductors, so heat moves quickly from the hot end of the spoon to the handle.
Wrong choices
- Convection: Convection is heat carried by moving liquid or gas. The spoon is a solid.
- Evaporation: Evaporation is liquid turning into gas. It does not carry heat up a spoon.
- Radiation: Radiation is heat carried by waves, like sunlight. The heat here moved through the metal by contact.
Question 2. A heater warms the air near the floor. The warm air rises, cooler air sinks to take its place, and the air keeps circulating. What is this kind of heat transfer called?
- ① Conduction
- ② Radiation
- ③ Insulation
- ④ Convection
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Answer: ④ Convection
Key point: Convection: heat carried by moving fluid (liquid or gas)
Warm air is less dense, so it rises. Cooler, denser air sinks. This circulating movement (a convection current) carries heat around the room.
Wrong choices
- Conduction: Conduction is heat moving through direct contact, mainly in solids. Here the air itself is moving.
- Radiation: Radiation travels as waves and does not need moving air.
- Insulation: Insulation slows heat transfer. It is not a way heat moves.
Question 3. Energy from the Sun reaches Earth after crossing empty space. How does this energy travel?
- ① Convection
- ② Radiation
- ③ Friction
- ④ Conduction
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Answer: ② Radiation
Key point: Radiation can travel through empty space
Radiation is energy carried by electromagnetic waves, such as light and infrared. These waves do not need matter, so they can cross the near-empty space between the Sun and Earth.
Wrong choices
- Convection: Convection needs a moving liquid or gas. Space is almost empty.
- Friction: Friction is a force between surfaces. It does not carry energy across space.
- Conduction: Conduction needs particles touching each other. Space is almost empty.
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