So far, you have already recognized the relationship between heat and temperature. So how do they differ? Go back to your previous experiments and analyze your findings. Then try to answer questions below.
Which has a higher temperature, 1 cup of boiling water or 1 teapot of boiling water? Which can transfer more heat, 1 cup of boiling water or 1 teapot of boiling water? Explain your answer.
Which can transfer more heat, a cup of boiling water or a cup of tap water? If you increase the amount of the boiling water and tap water twice, will their temperature change? Explain your answer.
Which can transfer more heat, a cup of boiling water or 1 basin of tap water? (You may try this out if you have time.)
So how are heat and temperature different? Well, here are the important points to consider about the difference between heat and temperature. First, heat is a form of energy while temperature is not a form of energy. Temperature is a measure of the average kinetic energy of the particles and it does not depend on the mass of the object. It can be measured directly with the use of thermometers. Heat cannot be measured directly. But you can make use of the measurable quantities related to heat to determine how much heat (Q) is absorbed by the object. These are the change in temperature (∆T), mass (m), and specific heat capacity (c) of the object. The relation among these quantities is expressed as:
Q m c T
.52 Links
Chalfant, H., Peyron, M., Rachke, C. (2005, Fall). Heat and temperature. Sci Ed, 491. Retrieved from
http://www.biol.wwu.edu/donovan/SciEd491/HeatTempUnit.pdf Expansion and contraction. (n.d.). Retrieved from
http://schools.cbe.ab.ca/b682/pdfs/Science%207/Heat-and-Temperature-Unit3_T4_T6.pdf
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ELECTRICITY
Overview
Electricity is a part of our daily lives. Many of the activities we do everyday depend on electricity. The discovery of electricity changed people’s lives. Can you watch your favorite show on TV without electricity? Can you use your computers without electricity? Imagine our life today without electricity.
You have been learning a lot about electricity from Grade 3 to Grade 7. You have learned about its sources and uses; what materials make good conductors of electricity; what makes up an electric circuit; and how electrical energy is transferred or transformed into other forms of energy.
In this module, you will learn more about electricity. There are three quantities that you should be familiar with in the study of electricity. These are electric current, voltage, and resistance. You will use the relationships among these quantities in learning about circuit connections. You will also learn that some of the safety precautions you have been warned about can be explained by the relationships among voltage, current, and resistance.
At the end of this module you should be able to answer the following questions:
How do voltage and resistance affect electric current?
What are the safety precautions needed in using electricity?
Unit 1
MODULE
4
Suggested time allotment: 6 to 8 hours
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Electric Current
In Grade 7, you learned that a circuit is any arrangement of a source of energy (battery), connecting wires, and a load (e.g. bulbs). You also learned that a complete or a closed circuit provides a path for electrical charges to flow. Electric current is a measure of the number of electrical charges passing through a cross-section of a conductor in a given time. The direction of conventional current or simply current is from the positive terminal of the battery to the negative terminal.
The symbol for current is capital letter I. The unit, ampere (A), is named after Andre-Marie Ampere, a French physicist who made important contributions to the theory of electricity and magnetism.
An ammeter measures electric current. Figure 1 shows how the ammeter is connected in a circuit. The positive terminal of an ammeter is connected to the positive terminal of the energy source (e.g. battery) while the negative terminal is connected to the negative terminal of the energy source as shown in Figure 1.
Figure 1. Ammeter connected in a circuit
Voltage
What makes the charges move in a closed circuit? In Module 2, you learned that when work is done on an object, energy is transferred which can become energy of motion of the object. In a circuit, work must be done on the charges to make them move. The battery supplies the energy in electric circuits. The chemical energy in the battery is transformed to electrical energy. This electrical energy moves the charges in a circuit.
A battery consists of several dry cells or wet cells. Both dry and wet cells contain a conducting medium called electrolyte. The batteries we use in flashlights and watches are dry cells.
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The symbol for voltage is capital letter V. The unit, volts (V), is named after the Italian physicist Alessandro Volta who invented the voltaic pile, the forerunner of what we now call the dry cell.
A voltmeter measures voltage. Figure 2 shows how the voltmeter is connected in a circuit. The voltmeter should be connected across the load being tested. The positive terminal of a voltmeter is connected to the positive terminal of the bulb while the negative terminal is connected to the negative terminal of the bulb as shown in Figure 2.
Figure 2. Voltmeter connected across the load
If voltage is needed for charges to flow, how does the amount of voltage affect current? Find out in Activity 1.