# Resistance and Resistors

### Overview

This lesson introduces the most important equation in electronics. The lesson looks at the concept of resistance as a physical property of a component before defining and using the resistor equation that links voltage, current and resistance. The second part of the lesson considers all the different types of resistor with particular attention to LDRs and Thermistors.

### Learning Objectives

• Understand the meaning of resistance of a component in a circuit
• Recall and use the resistor equation
• Rearrange the resistor equation and understand how to use different units for current, voltage and resistance
• Appreciate that there are many different types of resistors and recognise the circuit symbols for different resistors
• Appreciate the behaviour of LDRs and Thermistors

### Lesson Content

Reading: Read the webpage about resistance. Learn the resistor equation and understand how to rearrange the equation for current and voltage. Work through each of the three examples carefully.

Video (10 min): Watch the video that demonstrates the connection between voltage and current for a fixed resistor and demonstrates the resistor equation.

Video (4 min): Watch the Interactive White Board video demonstrating how to use the resistor equation in the context of a simple circuit.

Reading: Read about the different types of resistors. Pay particular attention to the behaviours of LDRs and Thermistors and use the powerpoint to read about these components in more detail. Make sure your notes are complete for this lesson and include a note about some of the different types of resistors. Review the resistor circuit symbols that should be familiar.

### Lesson Review

Review your learning by working through the presentations or notes which summarise the website content.

Presentation: Powerpoint download. A more detailed look at each of the different types of resistor.

### Self Assessment

Complete either the questions (pdf download) OR the on-line quiz. They are the same questions.

Quiz: Online quiz about the resistor equation.

### Self Evaluation

I can:

• Understand the action of a resistor in a circuit
• Use the resistor equation to calculate resistance, voltage or current
• Use the resistor equation with non-standard values such as current measured in milliamps
• Appreciate the importance of tolerance and power rating when selecting resistors
• Recognise a range of different resistors
• Recall that the resistance of an LDR decreases with increasing light level
• Recall that the resistance of a thermistor decreases with increasing temperature
• Recognise the circuit symbols for different resistors