Physical Science Grade 10 www.learnxtra.co.za SESSION 10: ELECTRIC CIRCUITS KEY CONCEPTS: In this session we will focus on: Potential Difference (emf) Current Circuit Diagrams Resistance Resistors in Series Resistors in Parallel X-PLANATION Potential Difference (emf): Definition: Potential difference is the work done per unit charge. The unit of potential difference is the volt (V), which is defined as 1 joule per coulomb. Emf: Potential difference across the terminals of a battery that is not in a complete circuit. Maximum amount of work per coulomb of charge the battery can do. Measured with a voltmeter Connected in parallel Current: Definition: The rate at which charges moves past a fixed point in a circuit. The unit of current is the ampere (A) which is defined as one coulomb per second Measured with an ammeter Connected in series Example 1: An amount of charge equal to 45 C moves past a point in a circuit in 1 second, what is the current in the circuit? Brought to you by Page 1 Physical Science Grade 10 www.learnxtra.co.za Example 2: Write definitions for each of the following: a. b. c. ampere coulomb voltmeter Circuit Diagrams: Component Symbol Usage Light Bulb Glows when charge moves through it. Battery Provides energy for charge to move. Switch Allows a circuit to be open or closed. Resistor Resists the flow of charge. Voltmeter Measures potential difference. Ammeter Measures current in a circuit Connecting Lead Connects circuit elements together. Brought to you by Page 2 Physical Science Grade 10 www.learnxtra.co.za Resistance: Definition: Resistance slows down the flow of charge in a circuit. The unit of resistance is the ohm (Ω) which is defined as a volt per ampere of current. Resistors in Series: - Current is the same everywhere Voltage is divided Resistance increases Resistors in Parallel: - Current is divided Voltage is the same Resistance decreases X-AMPLE QUESTIONS Question 1: Three identical light bulbs A, B and C are connected in an electric circuit as shown in the diagram below. Brought to you by Page 3 Physical Science Grade 10 www.learnxtra.co.za a. b. c. How bright is bulb A compared to B and C? How bright are the bulbs after switch S has been opened? How do the currents in bulbs A and B change when switch S is opened? Question 2: There are 3 resistors in parallel with resistances of 3 Ω, 4 Ω and 11 Ω. What is the total resistance of the parallel combination? Question 3: The same three resistors as above are now arranged in series, 3 Ω, 4 Ω and 11 Ω. What is the total resistance of the series combination? Question 4: In a series circuit there are 3 resistors with voltages of 2 V, 5 V and 8 V, what is the voltage across the battery in the circuit? Question 5: In a parallel circuit there are 3 resistors with voltages of 2 V, 2 V and 2 V, what is the voltage across the battery in the circuit? Brought to you by Page 4