Basic 8 · Science · Heat and Temperature
Heat, Temperature and Electricity Transmission
In this topic you will discuss the differences and the relationship between heat and temperature in the environment, and explain how electricity is transmitted from power stations to users.
By the end of these notes you should be able to:
- Distinguish heat from temperature
- Explain how heat and temperature are related
- Explain how electricity is transmitted
What you already know
- Energy conversion
Copy everything that has a blue line on its left into your notebook. The other parts are for reading.
Lesson 1
- Strand
- Forces & Energy
- Sub-strand
- Heat and Temperature
- Indicator
- B8.4.1.3.1 – Discuss the differences and the relationship between heat and temperature in the environment
Introduction
A bucket of warm water can melt more ice than a cup of hot tea. Heat and temperature are not the same thing.
1. Definitions
| Feature | Heat | Temperature |
|---|---|---|
| meaning | energy that flows from hot to cold | how hot or cold something is |
| depends on | mass, temperature and substance | average particle movement |
| unit | joule (J) | degree Celsius (°C), kelvin (K) |
| measured with | a calorimeter, by calculation | a thermometer |
2. A Particle View
All matter is made of moving particles. When a substance is warmed, its particles move faster. Temperature tells us the average kinetic energy of the particles. Thermal energy is the total energy of all the particles. A big bucket of warm water holds more thermal energy than a small cup of hot tea, because it has many more particles, even though the tea has the higher temperature.
3. Heat Flow
Heat always flows from a hotter body to a colder one until they reach the same temperature, a state called thermal equilibrium. Your tea cools because heat flows into the air. Ice melts in your hand because heat flows from your skin into the ice. Cold is not something that flows: the feeling of cold is due to heat leaving your body.
4. Measuring Temperature
A thermometer works because liquid expands when heated. Most laboratory thermometers contain coloured alcohol or mercury. Mercury thermometers are now being phased out, because mercury is poisonous. Digital thermometers use electronic sensors. To change from Celsius to kelvin, add 273: 27 °C = 300 K. Normal human body temperature is about 37 °C.
New words
- heat
- Energy flowing from hot to cold.
- temperature
- A measure of hotness.
- thermal equilibrium
- The state of equal temperature.
- kelvin
- The SI unit of temperature.
Summary
- Heat is energy in transfer, and temperature measures hotness.
- Heat flows from hot to cold until temperatures are equal.
- Particles move faster at higher temperatures.
Class activity: Hot and Cold Water
- Mix equal amounts of hot and cold water.
- Measure the temperature before and after.
- Explain what you find.
You need: Non-mercury laboratory thermometer or digital thermometer, Beaker of warm water, Beaker of cool water
Exercises
Answer in your exercise book first, then check your answers.
1. Temperature is measured with a…
- A. thermometer
- B. ruler
- C. balance
- D. ammeter
Show answer
Answer: thermometerMeasure.2. The SI unit of heat is the…
- A. joule
- B. degree
- C. newton
- D. metre
Show answer
Answer: jouleEnergy.3. Heat flows from hot to cold.
- A. True
- B. False
Show answer
Answer: TrueDirection.4. 27 °C is equal to ______ K.
Show answer
Answer: 300Add 273.5. Give one difference between heat and temperature.
Show answer
Answer: Heat is energy measured in joules, while temperature measures hotness in °C.Definitions.6. Why does a bucket of warm water contain more thermal energy than a cup of hot tea?
Show answer
Answer: It has far more particles, so the total energy is greater.Mass.
Lesson 2
- Strand
- Forces & Energy
- Sub-strand
- Heat and Temperature
- Indicator
- B8.4.1.3.1 – Discuss the differences and the relationship between heat and temperature in the environment
Introduction
At Bolgatanga in March or at Cape Coast by the sea, the temperature feels very different. Heat and temperature shape our environment.
1. How Heat and Temperature Are Related
Adding heat to something usually raises its temperature. The size of the rise depends on the mass of the object and the material. Water needs a lot of heat to warm up, so it has a high specific heat capacity. Sand needs less. That is why beach sand burns your feet at midday while the sea stays cool, and why coastal areas have milder temperatures than inland places.
| Factor | Effect |
|---|---|
| mass | More mass needs more heat. |
| material | Water needs more heat than sand or iron. |
| heat supplied | More heat causes a greater rise. |
2. Heat Transfer
| Method | How it works | Example |
|---|---|---|
| conduction | through solids, by touch | a metal spoon in hot soup |
| convection | by moving liquids and gases | sea breeze |
| radiation | by waves, needs no medium | sunshine |
3. Sea Breezes
- By day, land warms faster than the sea.
- Warm air over land rises.
- Cooler air from the sea flows in to take its place.
- This is a sea breeze.
- At night, land cools faster, and a land breeze may flow out to sea.
4. Heat and Temperature in Daily Life
Thatch roofs keep houses cooler than metal ones, since thatch is a poor conductor. White clothes reflect sunlight, and dark clothes absorb it. Cities are hotter than the countryside, since concrete stores heat and few trees give shade. The Harmattan brings cool nights and hot days because dry air and clear skies let heat escape quickly. Understanding these effects helps us to design better houses and live comfortably.
New words
- conduction
- Heat moving through a solid.
- convection
- Heat moving by flowing fluids.
- radiation
- Heat moving as waves.
- sea breeze
- Cool air blowing from sea to land.
Summary
- Heat raises temperature, depending on mass and material.
- Heat travels by conduction, convection and radiation.
- Sea breezes and building materials show these ideas at work.
Class activity: Sand and Water
- Put sand and water in separate cups in the sun.
- Record their temperatures over time.
- Explain any difference.
You need: Non-mercury laboratory thermometer or digital thermometer, Beaker of warm water, Beaker of cool water
Exercises
Answer in your exercise book first, then check your answers.
1. Heat from the Sun reaches us by…
- A. radiation
- B. conduction
- C. convection
- D. sound
Show answer
Answer: radiationNo medium.2. A sea breeze occurs because…
- A. land warms faster than sea
- B. sea is hotter
- C. the moon shines
- D. rain falls
Show answer
Answer: land warms faster than seaConvection.3. Metal is a good conductor of heat.
- A. True
- B. False
Show answer
Answer: TrueSpoon.4. Heat moving through a solid is ______.
Show answer
Answer: conductionTouch.5. Why do people wear white in hot weather?
Show answer
Answer: White clothes reflect sunlight and absorb less heat.Radiation.6. Why is Cape Coast cooler than Bolgatanga in March?
Show answer
Answer: The sea has a high heat capacity and sea breezes cool the coast, while Bolgatanga is far inland.Climate.
Lesson 3
- Strand
- Forces & Energy
- Sub-strand
- Electricity and Electronics
- Indicator
- B8.4.2.1.1 – Explain how electricity transmission occurs
Introduction
The electricity that lights your classroom may have been generated hundreds of kilometres away. How does it reach you?
1. The Journey of Electricity
- Power stations generate electricity.
- A step-up transformer raises the voltage.
- High-voltage lines carry electricity across long distances.
- Substations use step-down transformers to reduce the voltage.
- Distribution lines carry it through towns.
- Pole-mounted transformers reduce the voltage to about 230 V.
- Service lines bring it to meters in homes.
2. Why High Voltage?
When a current flows through a wire, some energy is lost as heat. A high current causes high losses. Using a higher voltage means that the same power can be carried by a much smaller current. This greatly reduces energy loss. So transformers step up the voltage for transmission. Since high voltage is very dangerous, it is stepped down before it reaches users.
3. Ghana's Electricity System
| Organisation | Role |
|---|---|
| VRA and other generators | generate electricity |
| GRIDCo | transmits high-voltage power |
| ECG | distributes power in the south |
| NEDCo | distributes power in the north |
| Energy Commission | regulates and advises |
GRIDCo's lines operate mainly at 161 kV and 330 kV. Ghana also sells electricity to neighbouring countries through the West African Power Pool.
4. Using Electricity Safely
Safety: Never touch fallen cables, climb pylons or fly kites near power lines. Do not touch switches with wet hands. Report damaged wires to the ECG or NEDCo. Illegal connections can kill.
Wires need insulators, usually of ceramic or glass, to stop current from leaking to the pylon. Electricity meters record how much energy each home uses, in kilowatt-hours. Illegal connections cause losses to the country and can start fires.
New words
- transformer
- A device that changes voltage.
- transmission
- Carrying electricity over long distances.
- substation
- A place where voltage is changed.
- voltage
- The electrical push, measured in volts.
Summary
- Electricity travels from generators through transformers and lines.
- High voltage reduces energy loss during transmission.
- GRIDCo transmits, and ECG and NEDCo distribute electricity.
Class activity: Transmission Chain
- Draw the path of electricity from Akosombo to your school.
- Mark each change in voltage.
- Add three safety rules.
You need: Printed Ghana electricity-transmission diagram, Printed transmission-stage cards, String arrows
Exercises
Answer in your exercise book first, then check your answers.
1. A device that changes voltage is a…
- A. transformer
- B. thermometer
- C. battery
- D. bulb
Show answer
Answer: transformerVoltage.2. Which company transmits high-voltage power in Ghana?
- A. GRIDCo
- B. ECG
- C. NEDCo
- D. VRA
Show answer
Answer: GRIDCoTransmission.3. High voltage reduces transmission losses.
- A. True
- B. False
Show answer
Answer: TrueLower current.4. Mains voltage in Ghana is about ______ V.
Show answer
Answer: 230Domestic.5. Give two electrical safety rules.
Show answer
Answer: Do not touch fallen cables, and do not touch switches with wet hands.Any two.6. Why is electricity transmitted at high voltage?
Show answer
Answer: The same power is carried with a smaller current, which reduces heat losses.Physics.
Homework
- Draw the path of electricity to your home and list three safety rules.