Unit 2 About Physics: Electricity and Electronics, Slides of Engineering Physics

Download Unit 2 About Physics: Electricity and Electronics and more Slides Engineering Physics in PDF only on Docsity! In unit 2 we will learn about the physics of electricity and electronics. This includes circuits, Ohm’s law, resistance, electrical energy and power, electromagnetism and electronic components. What is electricity? The atom An atom is a fundamental unit of matter made up of protons (with a positive charge) neutrons (neutral – no charge) electrons (with a negative charge) What is electricity? Everything is made of atoms which contain POSITIVE particles called PROTONS and NEGATIVE particles called ELECTRONS. Proton (+) Neutron Electron (-) An atom will usually have the same number of positives and negatives This makes the atom NEUTRAL. Proton (+) Neutron Electron (-) Electrical Charge The charge on a proton is 1.6 x 10-19C which is the same size as the charge on an electron. What is electricity? Electrons have a negative charge (Q) measured in coulombs (C). Electrons move round a circuit from negative to positive (remember like charges repel, opposites attract) giving rise to an electric current. 26, oppositelycharged oljectsathact = AND objects with like charges repel What is electricity? So electricity is… movement of charge round a circuit. We call this electric current. The atrows show the direction of the electrons movement Charge, Current & Time Electric current is given the symbol I Electric current is the movement of negative charges (electrons) in a circuit Charge, Current & Time This can be rearranged as or ItQ  I Q t  Key words: series, current, ammeter, voltmeter, battery, resistor, variable resistor, fuse, switch, lamp, voltage By the end of this lesson you will be able to: Draw circuit diagrams to show the correct positions of an ammeter in a series circuit. Draw and identify the circuit symbols for an ammeter, voltmeter, battery, resistor, variable resistor, fuse, switch and lamp. State that in a series circuit, the current is the same at all positions. Different types of circuit There are different ways in which you can connect cells and components (such as lamps) to create a circuit: series parallel a mixture of both Series Circuit A series circuit has only one electrical path. You can trace from one side of the battery to the other, through each component, without lifting your finger from the page. Physics Animations – Series Circuits Name that component Voltmeter Lamp Fuse Switch Cell Battery Variable resistor Resistor Ammeter On the back of p2 carefully draw each symbol and label – in pencil! Build a series circuit On the worksheet you will find four building circuit activities. Follow the instructions carefully! Answer each question as you go. Make careful observations. Lesson 2 build a series circuit.pub Activity 2 fT . Bulbs are much dimmer! Activity 3 - Change your circuit… Move your ammeter to different positions in the series circuit. Make a note of the positions each time, and of the current at each position. What can you say about the current in a series circuit? Successful Circuit Diagrams On your worksheet you have drawn a circuit diagram. To be successful at circuit diagrams: • use a ruler and pencil • draw components carefully • draw wires as straight lines (with corners as • right angles!) • make sure all components are correctly draw • and joined in the circuit. Notice in this circuit, current is the same at all points Series Circuits and Current We are measuring the current I in a series circuit. What have we observed? We find that the current is the same at all points. How can this be written mathematically? I1 = I2 = I3 = I4 and so on Virtual Int 2 Physics – Electricity & Electronics – Circuits – Series Circuits Think… How could you make use of a series circuit to investigate which materials are conductors and which materials are insulators? Which components would you need? What would you observe? Key words: series, parallel, ammeter, current, By the end of this lesson you will be able to: Draw circuit diagrams to show the correct positions of an ammeter in a parallel circuit. Draw and identify the circuit symbols for an ammeter, and lamp. State that in a series circuit, the current is the same at all positions. State that in a parallel circuit, the sum of the current in the branches adds up to the current drawn from the supply. Quick Quiz What is a series circuit? What is the symbol for current? What are the units of current? What is the relationship between current and time? What do we know about the current in a series circuit? How do we measure current? Draw the symbol for this. Describe how to measure current in a series circuit. Build another circuit Build a series circuit which includes a 6V battery, a 6V lamp and an ammeter. Draw the circuit diagram for your circuit: What sort of circuit is this? We have constructed a parallel circuit. What does the circuit diagram look like? Try drawing it on Crocodile Physics. Draw the circuit diagram below Parallel Circuit We have constructed a parallel circuit. This is a circuit with different branches. When it reaches a junction, the current can divide and take different branches. A SIMPLE CIRCUIT SWITCH CELL Clo Si, e the ‘sy WA QF happ &hs. ~~ LIGHT BULB A SIMPLE CIRCUIT 2A 2A 2A 2A 2A 2A 1A 1A A Series Circuit 1A 1A 1A 1A 1A What have you learned today? Key words: voltage, potential difference, voltmeter, series, parallel By the end of this lesson you will be able to: Draw and identify the circuit symbols for a voltmeter, battery, and lamp State that the voltage of a supply is a measure of the energy given to the charges in a circuit. Draw circuit diagrams to show the correct positions of a voltmeter in a circuit. State that the sum of potential differences across the components in series is equal to the voltage of the supply. State that the potential difference across components in parallel is the same for each component. What is electricity? What is a voltage? What is a volt? Discussion Demonstration Voltage in series and parallel If there is a bulb in the circuit, it is converted from to http://www.members.shaw.ca/len92/current_animation.gif The amount of electrical energy the electrons have at any point in a circuit is known as their “potential”. As they move the electrons transfer energy into other forms. This means at any two points the electron has different amounts of energy. Electrons start with (for example) 6J of energy. They have “potential”. As they pass through the bulb, some of the energy is converted to light. Electrons which have passed through the bulb have less energy. Or less “potential”. There is a “potential” difference in the circuit Potential Difference or Voltage (V) A 1.5 V battery will give how much energy to each coulomb of charge passing through the battery? 1.5 J Potential Difference or Voltage (V) A battery with a p.d. of 6V will give how much energy to each coulomb of charge passing through the battery? 6 J Voltage or p.d. Voltage (or p.d.) is measured in volts and is given the symbol V You can’t measure voltage… in a circuit through a circuit through a component flowing Build a series circuit Build a series circuit which contains a 6V battery, two 6V lamps, and a meter used for measuring potential difference across each lamp. What is the meter called? Where is it positioned in the circuit? Drawing a circuit diagram Now draw a circuit diagram of the series circuit which you built. Remember to use a ruler and pencil, draw components carefully, draw wires as straight lines (with corners as right angles!), and make sure all components are correctly draw and joined in the circuit. Parallel Circuits and Voltage We are measuring the potential differences in a parallel circuit. What have we observed? How can this be written mathematically? Tasks & Homework Yellow Practice Questions: 2.10, 2.11 Numerical Questions: p33-36 qu 5-14 Complete for homework for Tuesday 27th November What have you learned today? Key words: electrical resistance, voltage, current, Ohm’s law, ohms, resistor, variable power supply By the end of this lesson you will be able to: State that V/I for a resistor remains approximately constant for different currents. State that an increase in resistance of a circuit leads to a decrease in the current in that circuit. draw the symbol or a variable power supply and resistor. Key words: electrical resistance, voltage, current, Ohm’s law, ohms, resistor, variable power supply By the end of this lesson you will have practised: building a series circuit using an ammeter and a voltmeter to find current and voltage. graphing results Resistors The symbol for a resistor is ef Relationship between current and voltage in a resistor I / Amps p.d. / Volts Straight line through the origin tells us that current is directly proportional to voltage The ratio V/I is constant and is equal to resistance in the circuit. Relationship between current and voltage in a resistor R I V  I V R resistance is constant The constant elyapproximat is Relationship between current and voltage in a resistor I V R  Ohm’s Law IRV  What can you say about current and resistance for a fixed voltage? Complete the sentences. As resistance increases, the current As resistance decreases, the current Varying Resistance The opposition to current or resistance of a material (measured in Ω) depends on several things. Think and discuss what some of these might be. Varying Resistance The opposition to current or resistance of a material (measured in Ω) depends on - type of material (the better the conductor, the lower the resistance) - length of material (the longer the material, the higher the resistance) - thickness of material (the thinner the material, the higher the resistance) - temperature of material (the higher the temperature, the higher the resistance) Variable Resistors In the above diagram, if the slider is moved in the direction A→B the resistance will increase because the length of wire through which the current passes increases. Uses of Variable Resistors? Variable resistors can be used • as volume or brightness controls on televisions • volume control on MP3 players • light dimmer switches. Key words: resistance, series, parallel, ohms, ohmmeter By the end of this lesson you will be able to: State the relationships between total resistance and individual resistances in series and parallel circuits Carry out calculations involving the relationships between resistors in series and in parallel