Resistors

1. Resistors In this presentation you will: • discover how to use multimeters to measure resistance • identify how resistors can be used in circuits Next >

2. Introduction Resistors are commonly used in electronic circuits to control voltage and current. There are several different types of resistors that can be used. Next >

3. Resistors The type of resistor used has to be appropriate for the application. A low power resistor. A high power resistor. Several resistors in one package (resistor arrays). A rheostat (variable resistor) for experimentation. Next >

4. Resistors The value of a resistor, its resistance, is measured in ohms (W). This indicates how much it reduces the current flow. A higher value of resistance reduces the current flow more than a lower value resistance. Next >

5. 1 kW = 1,000 W 1 MW = 1,000,000 W Powers of 10 It is common to use W, kW, and MW values for resistors. There are 1,000 W in a kW (kilohm).There are 1,000 kW in a MW (megohm).So, there are a million ohms in a MW. For example, a 4,700 W resistor is usually expressed as 4.7 kW. These multiples should be used to ensure that there will never be more than three digits in a resistor value. Next >

6. Question 1 How many ohms does a 3.9 kW resistor have? A) 39 B) 390 C) 3,900 D) 39,000 Next >

7. Question 1 How many ohms does a 3.9 kW resistor have? A) 39 B) 390 C) 3,900 D) 39,000 Next >

8. Resistor Color Code Some resistors are too small for their values to be printed on them. The value is displayed by a series of colored bands. The simplest color code is one that has four bands. In order to read the code, it is necessary to get the resistor the right way round. Arrange the resistor so that the band on its own is on the right. Next >

9. Band D Band A Band B Band C Resistor Color Code The table gives a list of the colors and their associated values. Write down the value for band A. Write down the value for band B. Band C gives the number of zeros to add to the two numbers you have already written down. If band C is black, add no zeros. The number you have written down is in ohms. Convert it to kilohms or megohms if necessary. Next >

10. Yellow Violet Red Gold 4 00 7 Band D Band A Band B Band C Resistor Color Code Here is an example: Band A is yellow: the value is 4. Band B is violet: the value is 7. Band C is red: add two zeros. This gives 4,700 W. This is equivalent to 4.7 kW or 4K7. Next >

11. C A B D Color Tolerance Resistor Color Code What about the fourth band, band D? This gives the tolerance of the resistor. It is often called the tolerance band. This indicates the accuracy of the value given by the first three bands. In the example, the fourth band is gold. This means the value is within 5% of 4K7. 5% of 4K7 is 235 W. So, the value is 4,700 ± 235 W (between 4,465 W and 4,935 W). Next >

12. Question 2 What is the color code for a 3.9 kW resistor? Number of Zeros Significant Figures Color A) orange, white, blue B) orange, white, black C) orange, white, yellow Gray D) orange, white, red Next >

13. Question 2 What is the color code for a 3.9 kW resistor? Number of Zeros Significant Figures Color A) orange, white, blue B) orange, white, black C) orange, white, yellow Gray D) orange, white, red Next >

14. 0.25 W 0.5 W 1 W Power A resistor also has a power rating. This is a measure of the energy it can dissipate safely. It is calculated by multiplying the voltage across the resistor by the current flowing through it. P = VI The unit of power is the watt (W). Resistors are usually available in 0.25 W, 0.5 W, and 1 W. Most electronic circuits in schools and colleges use low power resistors of 0.25 W. Next >

15. Light Dimmer Circuit This circuit has an option to control lamp brightness. In an ideal circuit, the connecting wires should have no resistance. 10 W Full brightness occurs when the lamp is connected directly to the power source. The lamp is dimmed when the switch connects the lamp to the power source through the resistor. Next >

16. Measuring Resistance Resistance is usually measured by a multimeter set to the ohmmeter range. The component must be removed from the circuit and connected to a multimeter. Next>

17. Resistors in Simple Science Experiments In order to make the math easier, we often use resistors with simple values in science. It is much easier to do calculations with values, such as 1 Ω, 2 Ω, 5 Ω, and 10 Ω rather than 2.2 Ω or 6.8 Ω. These resistors are often made by winding the correct length of wire around a former. Next >

18. Question 3 Connecting wires in circuits are usually made of copper. Why is this? A) Copper is an inexpensive metal B) Copper does not break C) Copper has a low resistance D) Copper does not react with other chemicals Next >

19. Question 3 Connecting wires in circuits are usually made of copper. Why is this? A) Copper is an inexpensive metal B) Copper does not break C) Copper has a low resistance D) Copper does not react with other chemicals Next >

20. Question 4 If the resistor in this circuit was changed from 10 W to 20W, what would happen to the lamp? A) It would get brighter 10 W B) It would dim C) There would be no change in the lamp Next >

21. Question 4 If the resistor in this circuit was changed from 10 W to 20W, what would happen to the lamp? A) It would get brighter 10 W B) It would dim C) There would be no change in the lamp Next >

22. Summary In this presentation you have seen: • different types of resistors • how to use a multimeter to measure resistance • how resistors can be used in circuits End >