Electric Circuit 3M Physics Past Paper PDF October 2024

ELECTRIC CIRCUIT 3M October 2024 bhg Electric Circuit Date Homework Topic/ Objectives bhg Physics 3M – October 2024 1 Electric Circuit 1 Inh...

ELECTRIC CIRCUIT 3M October 2024 bhg Electric Circuit Date Homework Topic/ Objectives bhg Physics 3M – October 2024 1 Electric Circuit 1 Inhalt 2 Simple electric circuit.......................................................................................................3 2.1 Rules for the experimental kit...................................................................................3 2.2 Small task................................................................................................................3 3 Electric current................................................................................................................5 3.1 Physical and conventional/ technical current direction..............................................5 4 Voltage............................................................................................................................8 4.2 Voltage source and ground.......................................................................................8 5 EveryCircuit Tutorial.........................................................................................................9 6 Lab: Circuit with switches...............................................................................................11 7 Resistance.....................................................................................................................14 7.1 Introduction via the circuit diagram.........................................................................14 7.2 Introduction via the physical origin.........................................................................15 7.3 Deﬁnition (Ohm’s law)............................................................................................15 7.4 Ohm’s resistor.......................................................................................................17 8 Resistors in series and in parallel....................................................................................20 9 Measurement of electrical quantities..............................................................................29 9.1 Multimeter.............................................................................................................29 9.2 Measurement of voltage.........................................................................................29 9.3 Measurement of current.........................................................................................30 9.4 Measurement of resistance....................................................................................30 10 Lab: Measurement of electrical quantities..................................................................31 10.1 Two light bulbs in series..........................................................................................31 10.2 Two light bulbs in parallel.......................................................................................32 10.3 General questions:.................................................................................................33 10.4 Build your own circuit.............................................................................................33 11 Lab: Potentiometer....................................................................................................34 11.1 Introduction...........................................................................................................34 11.2 Task.......................................................................................................................35 12 Lab: Resistance in ohmic and nonohmic conductor....................................................37 13 Electrical energy and power.......................................................................................39 14 Home electricity........................................................................................................44 14.1 Socket...................................................................................................................46 14.2 Health risk due to an electric shock........................................................................47 14.3 Safety measures....................................................................................................49 15 Lab: Installation of a lamp bulb..................................................................................53 bhg Physics 3M – October 2024 2 Electric Circuit 2 Simple electric circuit 2.1 Rules for the experimental kit Turn off the battery when you do not need it. Be careful with the components. You are responsible that the kit is complete, in order and everything is ﬁne when you put it back. In case there is a problem, let your teacher know. The light bulbs do not belong in the kit. They must be removed from the sockets. 2.2 Small task 2.2.1 Circuit symbols and circuit diagram Circuit symbols are standardized symbols for representing electronic components in a circuit diagram. A circuit diagram is a graphical representation of a circuit. Get to know your ﬁrst circuit symbols below. Voltage source / Conductor Lamp SPST switch SPSD switch voltage supply (cable) (*) (**) (***) *: The plus and minus signs are often omitted. The longer line indicates the positive terminal, the shorter line the negative terminal. **: SPST stands for single-pole single-throw ***: SPDT stands for single-pole double-throw (A list of many standardized symbols: https://en.wikipedia.org/wiki/Electronic_symbol) 2.2.2 Exercise Have a look at the list of the standardized symbols. Do you already know some symbols? If so, sketch them below and give a short explanation. bhg Physics 3M – October 2024 3 Electric Circuit 2.2.3 Exercise a) Draw a circuit diagram such that a bulb shines permanently. Use as few components as possible and use the correct symbols. b) Adjust your diagram in such a way that the bulb can be turned on/ off. c) Why does the bulb only shine when the switch is closed? bhg Physics 3M – October 2024 4 Electric Circuit 3 Electric current The movement of electrical charges is referred to as an electric current. The magnitude of the current is indicated by the electric current 𝐼𝐼 and indicates how much charge ﬂows through a conductor per second. Electric current The electric current 𝐼𝐼 indicates the amount of charges Δ𝑄𝑄 ﬂows through a conductor in a time interval Δ𝑡𝑡: Δ𝑄𝑄 𝐼𝐼 = Δ𝑡𝑡 The SI-unit is Ampere (A), C [𝐼𝐼] = A = s Remark: - Only free moving charges make up the current - The charges can be positive or negative. - In most situations, the charges are electrons that can freely move in metals. 3.1 Physical and conventional/ technical current direction The physical current direction is the actual direction of movement of the charge. This means that a positive charge moves from the positive pole to the negative pole. And a negative charge moves from the negative pole to the positive pole. Therefore, it depends on the sign of the charge. The conventional/ technical current direction has been deﬁned so that one does not always have to pay attention to the sign of the charge. It is always from plus to minus, i.e. in the same direction as the electric ﬁeld lines run. 3.1.1 Exercise a) A bulb is applied to a voltage supply via a copper wire as sketched below. Draw the physical and technical current direction to the sketch. b) Do you know any examples where the physical and technical current direction are the same? bhg Physics 3M – October 2024 5 Electric Circuit 3.1.2 Exercise a) If you increase the amount of charges that ﬂows through a conductor in the same time period, the current □ decreases. □ stays the same. □ increases. b) If the same charge ﬂows through a conductor in a shorter time period, the current □ decreases. □ stays the same. □ increases. c) If the current is decreased, the time until a certain amount of charges ﬂows through a conductor □ is shorter. □ is the same. □ is longer. 3.1.3 Exercise a) The amount of charges of 6 μC ﬂows through a conductor within 3 s. Determine the current in A and μA. b) Determine the amount of charges that ﬂows through a conductor within 2 s such that the current is 10 mA. bhg Physics 3M – October 2024 6 Electric Circuit c) Determine the number of electrons that ﬂow through a conductor within 1 s such that the current is 1 A. Hint: First, calculate the total amount of charges. Second, how many electrons are needed to get this charge? bhg Physics 3M – October 2024 7 Electric Circuit 4 Voltage 4.1.1 Exercise We already discussed the concept of voltage when we worked on the topic about electrostatics. a) What is voltage? Describe in our own words. b) What is the SI-unit of voltage? 4.2 Voltage source and ground A voltage source, e.g. a battery is an electronic component with two poles, one positive and one negative, which supplies an electric voltage between its two connection points. In common electronics, electrons are the free moving charges, therefore, the electrons move from the negative pole to the positive pole. An object connected to a conducting wire or copper pipe buried in the Earth is said to be grounded or connected to the ground (GND). The Earth can be considered an inﬁnite reservoir for electrons. In effect, it can accept or supply an unlimited number of electrons. By convention, ground sets the zero potential 𝜙𝜙 = 0 V. 4.2.1 Exercise Have a look at the electronic circuit below. Assume that the voltage source is a 9V-battery. Determine the electric potential on the poles of the battery. bhg Physics 3M – October 2024 8 Electric Circuit 5 EveryCircuit Tutorial EveryCircuit (http://everycircuit.com/) is a great circuit analysis tool. Use it to design and test your own electronic circuits. It is available on Google Chrome (web browser), Android and iOS. 1. Log in into your EveryCircuit account. If you don't have an account yet, create one. Link: http://everycircuit.com/ 2. Create a new circuit by clicking on “New circuit”. 3. Enter a title (e.g. `simple circuit with lamp') and select “private” per default. Select “unlisted” if you want to share it with speciﬁc persons. Select “public” if you want to share your awesome circuits with the world. 4. In the component bar on top, you can ﬁnd all the components available. The most important ones are colored in pinks. You should know them all eventually. 5. On the top right, click on your username and select “Settings”. Make sure that the “Conventional Current” check box is selected. It is good practice to get used to the conventional/ technical current. 6. Add a simple voltage source and a lamp by clicking on the respective symbols (left ﬁgure). Move them to a suitable position. Create wires by simply clicking on the nodes of the components (right ﬁgure). Note that you also need to connect to the ground to set the zero potential. 7. To delete a wire or component, select it (it gets colored in yellow) and press “Del” on your keyboard. bhg Physics 3M – October 2024 9 Electric Circuit 8. To run the animation, press the play button: 9. Now, your circuit should look like this: 10. The direction of the conventional current (not the electrons) is indicated by the moving green dots. In blue, you can see the electric potential before and after the lamp. At both the lamp and at the voltage source, the current is stated. Also, the lamp indicates how bright it shines. 11. Select the voltage source. The following tool bar appears: a. Click on the “tool” to change the properties of the component. b. Click on the “eye” to display the properties of the component in a graph. c. The four symbols on the right can be used to rotate and ﬂip the components, to cut all wires attached and to trash the component. 12. Click on the “tool”. Change the voltage such that the lamp... a. barely shines. b. shines very brightly. c. explodes! 13. To save a screenshot of your circuit, click on the `camera' button: 5.1.1 Exercise Play around with EveryCircuit and build your own circuit. Insert a screenshot of it here bhg Physics 3M – October 2024 10 Electric Circuit 6 Lab: Circuit with switches For the following exercises, proceed as follows: 1. Built the circuit using the experimental kit. 2. Draw the corresponding circuit diagram using the correct electronic symbols. 3. Build the circuit on EveryCircuit (http://everycircuit.com/) and use a meaningful name to save it. 4. Show your diagram and the set circuit to the teacher. Afterwards, you can continue with the next circuit. 6.1.1 Exercise Circuit in which two light bulbs can be switched on and off simultaneously. 6.1.2 Exercise Circuit in which two light bulbs can be switched on and off individually. bhg Physics 3M – October 2024 11 Electric Circuit 6.1.3 Exercise Circuit in which two light bulbs can be switched on and off alternatingly. I.e., one bulb has to be on, and one has to be off. 6.1.4 Exercise Consider a room with two doors and one light bulb. Besides each door there is a light switch. Both switches can turn on and off the light independently. bhg Physics 3M – October 2024 12 Electric Circuit 6.1.5 Exercise Now consider a room with one light bulb with three or more light switches. Each switch can turn on and off the light independently. To achieve this, you need a type of switch we have not discussed yet, namely the 4-way-switch. Note that this switch is not available on EveryCircuit. The 4-way-switch has two states: bhg Physics 3M – October 2024 13 Electric Circuit 7 Resistance 7.1 Introduction via the circuit diagram Consider the following simple circuit and build it using the experimental kit: What is the problem with this circuit? How do you call the shown situation? This situation can e.g. be caused by faulty electric devices. Why is it dangerous and how can you protect yourself against it? bhg Physics 3M – October 2024 14 Electric Circuit 7.2 Introduction via the physical origin Every material impedes the movement of charge carriers and therefore the ﬂow of electricity. The resulting friction (resistance) heats up the material. 7.3 Deﬁnition (Ohm’s law) If in a conductor the current is 𝐼𝐼 where the applied voltage is 𝑉𝑉, its resistance 𝑹𝑹 is deﬁned by 𝑉𝑉 𝑅𝑅 = 𝐼𝐼 The SI-unit for electrical resistance is given by Ohm Ω which is Volts per Ampere. 𝑉𝑉 [𝑅𝑅] = Ω = 𝐴𝐴 7.3.1 Exercise Built the following two circuits in EveryCircuit (https://everycircuit.com/): The left circuit has an Ohmic resistor (is often just called resistor) as the consumer. And the right circuit has an LED (light emission diode) as the consumer. Set the parameter for the LED as follows: bhg Physics 3M – October 2024 15 Electric Circuit a) Set different voltages and have a look how the current changes. Afterwards, calculate the resistance for each voltage-current pair. Ohm’s resistor V [V] 0 1 5 9.5 10 10.5 11 I [mA] R [Ω] LED V [V] 0 1 5 9.5 10 10.5 11 I [mA] R [Ω] b) Use the data and draw the I-U-diagram and the R-U-diagram. What do you observe. Describe in two to three sentences. How does Ohm’s resistor differ from a LED? bhg Physics 3M – October 2024 16 Electric Circuit If a voltage is applied to an electronic component, a certain current is generated. If the applied voltage is changed, the current also changes. The relationship between voltage and current is called a characteristic curve. Each component has a characteristic curve. 1. Diode / LED 2. NTC-resistor (has a lower resistance at higher temperatures, NTC= negative temperature coefficient) 3. Ohmic resistor 4. PTC-resistor (has a higher resistance at higher temperatures, PTC= positive temperature coefficient) 5. Varistor 7.4 Ohm’s resistor As you can see for many components, the resistance depends on the applied voltage. But there are components which have a voltage-independent resistance, such resistors are called ohmic resistors (however, the ‘ohmic’ is often omitted, i.e. when talking about a resistor, it can be assumed that one is talking about an ohmic resistor). Ohmic resistor The following applies to an ohmic resistor: 𝑉𝑉 𝑅𝑅 = = 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝐼𝐼 (And that is the actual Ohm’s law.) The symbol for an (ohmic) resistor is given by (American & European): Resistor Resistor (American) (European) bhg Physics 3M – October 2024 17 Electric Circuit Resistors can have different design: Left: Axial lead resistor, right: SMD resistor (SMD = surface mounted device) 7.4.1 Exercise a) If you increase the resistance, you need to □ increase □ decrease the voltage to maintain a certain current. b) If you decrease the voltage applied to a conductor, the current ﬂows through the conductor □ increases. □ decreases. c) A component is replaced in a circuit, which leads to a higher current with the same voltage. How has the resistance in the circuit changed? □ The resistance was increased. □ The resistance was decreased 7.4.2 Exercise a) Assume that a voltage of 24 V is applied on an ohmic resistor that leads to a current of 1.2 A. Calculate the resistance of the device. b) The maximal current that can safely ﬂow through the resistor is 2.3 A. What is the corresponding maximal voltage that can be applied on this resistor? bhg Physics 3M – October 2024 18 Electric Circuit 7.4.3 Exercise Have a look at the characteristics of two components: a) Which of the following statements are correct. □ If the voltage increases, the resistance of component 1 increases and the resistance of component 2 decreases. □ If the voltage increases, the resistance of component 1 stays constant and the resistance of component 2 decreases. □ If the voltage increases, the resistance of component 1 stays constant and the resistance of component 2 increases. □ If the voltage increases, the resistance of component 1 decreases and the resistance of component 2 increases. b) If a current of 0.75 A ﬂows through component 2. What is the corresponding voltage applied on the component. What is the corresponding resistance? c) Calculate the resistance of component 1. bhg Physics 3M – October 2024 19 Electric Circuit 8 Resistors in series and in parallel two bulbs in series two bulbs in parallel 1. Built a simple circuit that contains a single bulb. Observe the bulb’s luminosity. Draw the circuit diagram 2. Build a circuit that contains two identical light bulbs connected in series. Observe the luminosity. Draw the circuit diagram. 3. Build a circuit that contains two identical light bulbs connected in parallel. Again, observe the luminosity. Draw the circuit diagram. 4. You should observe signiﬁcant differences in the light bulb's luminosities. Explain these differences. Hint: What can you say about the total resistance of the two bulbs combined? 5. For your birthday party, you want to build your own chain of lights. Should you connect the light bulbs in parallel or in series? Why? bhg Physics 3M – October 2024 20 Electric Circuit Consider the two circuits shown below. In the circuit on the left, two resistors are connected in series. On the right, they are connected in parallel. In both cases, we could replace the two resistors with a single resistor Req. It has the same resistance as the combination of the two other resistors and is called equivalent resistor 𝑅𝑅𝑒𝑒𝑒𝑒. Equivalent resistance The equivalent resistance of multiple resistors 𝑅𝑅1 , 𝑅𝑅2 , … , 𝑅𝑅𝑛𝑛 connected in series is given by: 𝑅𝑅𝑒𝑒𝑒𝑒 = 𝑅𝑅1 + 𝑅𝑅2 + ⋯ + 𝑅𝑅𝑛𝑛 The equivalent resistance of multiple resistors 𝑅𝑅1 , 𝑅𝑅2 , … , 𝑅𝑅𝑛𝑛 connected in parallel is given by: 1 1 1 1 = + + ⋯+ 𝑅𝑅𝑒𝑒𝑒𝑒 𝑅𝑅1 𝑅𝑅2 𝑅𝑅𝑛𝑛 Derivations: Resistor in series: Resistor in parallel bhg Physics 3M – October 2024 21 Electric Circuit 8.1.1 Exercise Assume two resistors are connected in parallel. a) What is the current that the battery needs to provide? b) What is the current that ﬂows through each resistor? 8.1.2 Exercise All bulbs are identical in the following circuit. a) Mark all parts of the circuit carrying the same current with the same color. b) How bright are the bulbs compared to each other? Why? bhg Physics 3M – October 2024 22 Electric Circuit 8.1.3 Exercise Draw the corresponding diagram with a suitable equivalent resistor. 8.1.4 Exercise a) Find the equivalent resistance of the circuit. b) Find the applied voltage if a current of 𝐼𝐼 = 0.286 mA. c) Calculate the voltage drop at the 2 𝑘𝑘Ω resistor. bhg Physics 3M – October 2024 23 Electric Circuit 8.1.5 Exercise a) Determine the equivalent resistor. b) Determine the current provided by the battery. c) Determine the current through each resistor. d) Sanity check: Is the current conserved? Ensure that the sum of currents in c) is the same as the current in b). bhg Physics 3M – October 2024 24 Electric Circuit 8.1.6 Exercise a) Compare the brightness of the four identical bulbs shown in the ﬁgure below. b) What happens if bulb A fails and cannot conduct current? What if C fails? What if D fails? c) Check your answers by either building the circuit with the experimental kit or with EveryCircuit. bhg Physics 3M – October 2024 25 Electric Circuit 8.1.7 Exercise ? a) Assume that the battery provides a current of 321 mA. What is the resistance of the resistor indicated with “?”? b) Calculate the voltage drop at the 4 Ω resistor. bhg Physics 3M – October 2024 26 Electric Circuit 8.1.8 Exercise a) Find the equivalent resistance of the circuit. b) Calculate the current provided by the voltage supply. c) Calculate the voltage drop at the 2 Ω resistor. d) Calculate the current that ﬂows through the 4 Ω resistor. bhg Physics 3M – October 2024 27 Electric Circuit 8.1.9 Exercise*** a) Build a crazy circuit with resistors. The voltage supply should be 10 V. b) Calculate the equivalent resistor of it. c) Calculate the currents in the circuit. d) Use EveryCircuit to check your results. e) Challenge your neighbor. bhg Physics 3M – October 2024 28 Electric Circuit 9 Measurement of electrical quantities When working on electrical circuits, measuring voltage, current and resistance is essential. For basic measurement tasks a so- called multimeter can be used. 9.1 Multimeter A conventional multimeter can measure Voltage Current Resistance The symbols to indicate a certain measurement in the circuit diagram are shown in the table below: Voltmeter Amperemeter Ohmmeter 9.2 Measurement of voltage The multimeter used as the voltmeter can measure the voltage difference between two points in the electrical circuit, typically before and after a consumer. Measuring the voltage is probably the most important functionality of the multimeter because it does not inﬂuence the circuit and no adjustments in the circuit are needed. Step-by-step-instruction how to use the multimeter as the voltmeter: 1. Decide if direct current (DC) or alternating current (AC) occurs in the circuit If DC, arrange the turn switch to the corresponding section, If AC, arrange the turn switch to the corresponding section, 2. Decide which measurement range is relevant. The chosen range is relevant, e.g. if the range 20 V is chosen, then the maximal voltage that wants to be measure is 20 V. Attention: If the measured voltage is larger than the chosen range, the multimeter can break. So, if you do not know the range in advance, start with a large range and go to smaller range step-by-step to increase accuracy. bhg Physics 3M – October 2024 29 Electric Circuit 3. The voltmeter is connected in parallel to the consumer. The measuring tips are connected to COM (Common) that normally used for the point with the lower potential (voltage) and to V/Ω (Volt/ Ohm) that normally used for the point with higher potential. 4. Turn on the multimeter and measure the voltage. 9.3 Measurement of current Measurement of current using a multimeter works like the measurement of voltage. 1. Decide if direct current (DC) or alternating current (AC) occurs in the circuit. If DC, arrange the turn switch to the corresponding section,. If AC, arrange the turn switch to the corresponding section,. Remark: Some multimeters cannot measure alternating current. 2. Decide which measurement range is relevant. The chosen range is relevant. Again, if you do not know the relevant range, start with the large range und reduce it step-by-step to prevent any damage to the multimeter. 3. The voltmeter is connected in series to the consumer. The measuring tips are connected to COM (Common) that normally used for the point with the lower potential (voltage) and to 2A or 10A that normally used for the point with higher potential. 4. Turn on the multimeter and measure the voltage. 9.4 Measurement of resistance The measurement of resistance is almost like the measurement of voltage. It means: Arrange the turn switch to the corresponding section,. Chosen the relevant range. The Ohmmeter is connected parallel to the consumer. BUT the circuit needs to be open! (Meaning no current ﬂow possible!) bhg Physics 3M – October 2024 30 Electric Circuit 10 Lab: Measurement of electrical quantities Complete the job in the speciﬁed order and document all results. 10.1 Two resistors in series 1. Build a circuit with two resistors (100Ω) in series The circuit is powered by the battery. 2. Draw the corresponding diagram. 3. Do measurements in the circuit: a. Measure the voltage across each element and note the values. b. Compare the sum of all voltage drops in the circuit with the voltage applied to the circuit by the battery. Does it ﬁt your expectation. c. Use the multimeter to measure the currents before, after and between the resistors and note the measured values. d. Measure the resistance of each resistor and the total resistance. 4. Do the result ﬁt with your expectation? Explain in three to four sentences. Use physical arguments. 5. Show the result to the teacher. bhg Physics 3M – October 2024 31 Electric Circuit 10.2 Two resistors in parallel 1. Build a circuit with two resistors in parallel The circuit is powered by the battery. 2. Draw the corresponding diagram. 3. Do measurements in the circuit: a. Measure the voltage across each element and note the values. b. Compare the voltage drops in the circuit with the voltage applied to the circuit by the battery. c. Use the multimeter to measure the currents before the ﬁrst wire branching and after the second branching and note the measured values. d. Use the multimeter to measure the currents ﬂowing through the individual resistors. e. Measure the resistance of each resistor and the total resistance. 4. Do the result ﬁt with your expectation? Explain in three to four sentences. Use physical arguments. 5. Show the result to the teacher. bhg Physics 3M – October 2024 32 Electric Circuit 10.3 General questions: 1. Do the result ﬁt with your expectation? Explain in three to four sentences. Use physical arguments. 2. Why do you have to use different inputs on the multimeter to measure voltage and current? 10.4 Build your own circuit Build your own circuit and then use the multimeter! bhg Physics 3M – October 2024 33 Electric Circuit 11 Lab: Potentiometer 11.1 Introduction A potentiometer is a resistor with three connectors and a turning knob. The turning knob determines where the middle connector (called wiper) touches the resistor. The symbol for potentiometer is given by (American & European): Resistor Resistor (American) (European) Potentiometers are important for ﬁne adjustments, e.g. to control the volume or sound of an electric guitar or compensate variation other electrical components. Depending on how the potentiometer is connected to the circuit, it can achieved different things: 1. (Regular) resistor: If only the right and the left terminals are used, it acts as a regular resistor. The wiper is not connected. (But obviously, it does not make much sense to use a potentiometer in this way. It is better to use an ordinary resistor in the case.) 2. Variable resistor: If the wiper and only one end is used, the potentiometer acts as a variable resistor. If the knob is turned, the resistance is adjusted. The position of the wiper deﬁnes how much of the whole resistor has current ﬂowing through it. If the wiper is set to the left position, the entire resistor is bypassed, and the resistance is 0 Ω. If the wiper is set to the rightest position, the resistance is maximal. bhg Physics 3M – October 2024 34 Electric Circuit 3. Voltage divider: Depending on the knob’s position, the voltage at the voltage divider’s terminal (indicated by the two small circles) varies between 0 V and the voltage of the battery. Assume the circuit is powered by a 9 V battery. Then the voltage at the voltage divider can have any value between 0 V and 9 V depending on the knob’s position. 11.2 Task 1. Make sure you have understood the theory about the potentiometer. If not, ask your teacher. 2. Take the potentiometer and measure the maximal resistance. 3. Work with the experimental kit. If you want, you can combine two batteries to get a higher voltage. Connect the - terminal of a battery with the + terminal of the other battery: 3. Build a circuit where the potentiometer is used as a normal resistor. Measure the current and calculate the resistance. Does it match with 2.? 4. Build a circuit with a variable resistor and a light bulb. Make sure that you can regulate the bulb's brightness using the potentiometer. (Hint: May draw the circuit diagram.) bhg Physics 3M – October 2024 35 Electric Circuit 5. Use a voltmeter to measure the voltage at the potential divider's terminals. Make sure the voltage varies from 0V to the battery's voltage. (Hint: May draw the circuit diagram.) 6. With respect to the brightness of the light bulb, what is the difference between the situation in 4. and 5.? (Hint: Think about the extreme wiper positions.) 7. Additional exercise 1: Build the circuits in EveryCircuit. 8. Additional exercise 2: Goal: Understand how potential divider works in detail. Consider the following circuit where the voltage of the battery V, the (max.) resistance of the potentiometer 𝑅𝑅𝑝𝑝𝑝𝑝𝑝𝑝 as well as the resistance of the resistor R connected to the potential divider are given. Find a formula for the voltage provided by the voltage divider as a function of the wiper's position k which ranges from k = 0 (left) to k = 1 = 100% (right). bhg Physics 3M – October 2024 36 Electric Circuit 12 Lab: Resistance in ohmic and nonohmic conductor Recap: An ohmic resistor has a resistance that is constant for varying the applied voltage. A nonohmic resistor has a resistance that changes if the applied voltage changes. Goal: 1. Show that a resistor in the experimental kit is ohmic, i.e. the resistance is constant. 2. Show that a light bulb is nonohmic. How does resistance behave as a function of __voltage? Procedure: To determine the resistance at different voltages you obviously must apply different voltages to the conductor. You have two options to generate different voltages: o The use of a stabilized voltage source (ask your teacher for it) o The use of a self-built voltage divider (see last lab session) o Check each component what the maximal allowed voltage is and do not use more. Determine the resistance for different voltages Task: How can you determine the resistance? o How is resistance deﬁned? o What do you need to measure? o Think about the circuit needed and draw it. o Discuss with your teacher. bhg Physics 3M – October 2024 37 Electric Circuit Make the needed measurement and note the data you get for the resistor and the light bulb. Visualize the data in the diagram below in a qualitative way. resistance current voltage voltage What can you tell about the two components with respect to the characteristic curves (see section “Deﬁnition (Ohm’s law)) bhg Physics 3M – October 2024 38 Electric Circuit 13 Electrical energy and power In an electrical circuit, consumers convert electrical energy into another form of energy (e.g. heating) or use it to perform work (e.g. electric motor). They receive electrical energy from the electrons. These in turn receive their energy from the voltage source (e.g. battery). When passing the battery, the charge's electrical potential energy is increased by 𝑉𝑉 ⋅ 𝑞𝑞 because the battery is doing work on the charge. Thus, the chemical energy stored within the battery decreases by the same amount. When travelling through the resistor, the charge's electrical potential energy decreases by 𝑉𝑉 ⋅ 𝑞𝑞 (conservation of energy). Electrical power As we already know, power is the energy per time: 𝐸𝐸 𝑞𝑞 ⋅ 𝑉𝑉 𝑞𝑞 𝑃𝑃 = = = ⋅ 𝑉𝑉 = 𝐼𝐼 ⋅ 𝑉𝑉 𝑡𝑡 𝑡𝑡 𝑡𝑡 If we use the deﬁnition of resistance, we can get also the relations: 𝑉𝑉 2 𝑃𝑃 = = 𝐼𝐼 2 𝑅𝑅 𝑅𝑅 The SI-unit of power is of course watt (W). Electrical energy 𝐸𝐸 = 𝑃𝑃 ⋅ 𝑡𝑡 = 𝑉𝑉 ⋅ 𝐼𝐼 ⋅ 𝑡𝑡 The SI-unit is Joule (J). But it is very common to use kilowatt-hour if electrical energy is taken 1 𝑘𝑘𝑘𝑘ℎ = 3.6 ⋅ 106 𝐽𝐽 13.1.1 Exercise 𝑉𝑉 2 Use the deﬁnition of electrical power and Ohm's law to derive the expression 𝑃𝑃 = 𝑅𝑅 = 𝐼𝐼 2 𝑅𝑅. bhg Physics 3M – October 2024 39 Electric Circuit 13.1.2 Exercise The power of an electric kettle is 𝑃𝑃 = 1800 W that is connected to a household socket (𝑈𝑈 = 230 V). a) Calculate the current that ﬂows through the kettle. b) Calculate the internal resistance of the kettle. 13.1.3 Exercise A current of 0.2 A ﬂows through a 40 W light bulb. a) Calculate the applied voltage. b) How much energy is used in one hour. Give the result in J and kWh. c) What amount of charge ﬂows through the bulb during this time? bhg Physics 3M – October 2024 40 Electric Circuit 13.1.4 Exercise Let us consider the following three circuits. In all circuits, the batteries and resistors are identical: a) Compare the current 𝐼𝐼1 , 𝐼𝐼2 , 𝐼𝐼3. Hint: Express current 𝐼𝐼2 and 𝐼𝐼3 in terms of 𝐼𝐼1. b) Compare the total power 𝑃𝑃1 , 𝑃𝑃2 , 𝑃𝑃3. Express 𝑃𝑃2 and 𝑃𝑃3 in terms of 𝑃𝑃1. c) How long do the batteries last? Rank them. d) On EveryCircuit, built these circuits and conﬁrm the results. bhg Physics 3M – October 2024 41 Electric Circuit 13.1.5 Exercise Batteries are rated in terms of ampere-hours (Ah or mAh). For example, a battery than can deliver a current of 3 A for 5 h is rated at 15 Ah. a) What is the total energy stored in a 12 V battery rated at 55 Ah? Give the result in kWh. b) Assume that 1 kWh costs 20 Rp. What is the value of electricity than can be produced by this battery? 13.1.6 Exercise In 2023, the total consumption of electricity of Switzerland was 56.1 ⋅ 109 kWh a) Make internet research: How many people live in Switzerland? How much do you need to pay for 1 kWh in your town? b) What is the average annual electricity consumption of a single person in kWh? c) How much does a person need to pay for electricity in average in one year? bhg Physics 3M – October 2024 42 Electric Circuit 13.1.7 Exercise In a certain stereo audio system, each speaker has a resistance of 4 Ω. The system is rated at 60W on each channel. Each speaker circuit includes a fuse rated at a maximum current of 4 A. Is this system adequately protected against overload? bhg Physics 3M – October 2024 43 Electric Circuit 14 Home electricity So far, we have mainly dealt with batteries or stabilized voltage sources. But what about the current “coming out of the sockets” at home? What do you already know about this type of current? Discuss in groups of two. What type of current is this? What is the difference between this type of current and the one in circuits powered by batteries? What voltage is applied to a socket? A socket has three holes. What are these for? What are the differences between them? Faults in the electric installment can be dangerous and electric shocks can be life threatening. What safety measures are there at home? bhg Physics 3M – October 2024 44 Electric Circuit Direct current (DC) Alternating current (AC) Direction of current Voltage Voltage source Consumer bhg Physics 3M – October 2024 45 Electric Circuit 14.1 Socket Task: Make an internet research such that you can do the following: Label the socket and the plug. Specify the electric potential for each terminal. Where does the current ﬂow. What are the common wire colors used for each terminal? bhg Physics 3M – October 2024 46 Electric Circuit 14.2 Health risk due to an electric shock Electricity can be very dangerous, both for electric devices and for people and animals. How serious the consequences of an electric shock are depending on: Possible negative consequences of electric shock: For living beings: For devices and wires: Effect of electric shock with alternating current on the human body: AC-1: imperceptible AC-2: perceptible but no muscle reaction AC-3: muscle contraction with reversible effects AC-4: possible irreversible effects, could be directly fatal bhg Physics 3M – October 2024 47 Electric Circuit 14.2.1 Exercise a) Study the diagram about the effect of electric shock. At what current can an electric shock be fatal? b) As you probably know our bodies can conduct current and that is why an electric shock is possible. The ﬁgure on the right shows a highly simpliﬁed circuit diagram of the human body as a wiring network. Assume that a person stands on one foot and then touches the line/ phase conductor of a Swiss socket. What is the current ﬂowing through the body? Is it dangerous? c) Assume the same situation as before, but the person touches the phase with both hands. Is it now less dangerous? Calculate the current in this case. bhg Physics 3M – October 2024 48 Electric Circuit 14.3 Safety measures 14.3.1 Work on electrical devices If you want to work on an electrical device or install a new lamp. Then follow the rules for dealing with electricity: 1. Turn off the socket by deactivating the fuse(s) or unplug the device. 2. Use a phase tester to verify that the socket is turned off. Use a phase tester (see picture) as follows: Place a ﬁnger on the rear contact and insert the tip into all three holes of the socket one after the other. If the indicator in the phase tester lights up, this means you have found the line conductor (i.e. the phase) and the socket has not yet been turned off. Remark: Today, digital phase tester exists as well. Do always read the instructions well before you use the phase tester. 14.3.2 Installed safety measures in a house Example: For a lamp to light up, it must be connected to the line and neutral conductors. Now it is possible that the cable of the line conductor becomes loose and touches the lamp's metal housing. As soon as you touch the housing, you close the circuit and the current ﬂows through your body. With the following safety measures, you can ensure that this situation does not end too badly or (even better) does not occur at all. (Remark: We will come back to this example later.) 1. Circuit breaker (fuse): (German: Leitungsschutzschalter (Sicherung)) Every socket is protected by a circuit breaker. It monitors the current and interrupts the circuit if the current is too high. For example, the circuit breaker becomes active as soon as a short circuit occurs, as this causes a very high current. This prevents e.g. a cable ﬁre. Attention: The circuit breaker does not necessarily protect people from electric shocks! Modern circuit breakers look like in the picture below and can be found in the fuse box. 2. RCD (RCD for Residual Current Device: (German: FI-Schutzschalter, FI for FehlStrom) In the line conductor and neutral conductor, the current must always be equal, except that it ﬂows in opposite directions! If, for example, there's only current in the line conductor and not in the neutral conductor, this means that current ﬂows somewhere else: Either through the ground wire or through a person. Such a current is called a residual/fault/leakage current. The RCD checks whether such a residual current occurs by comparing the current through the line and neutral conductors. If there is a residual current, the circuit is interrupted. The RCD serves primarily to protect humans. Modern RCDs look like in the picture below and can be found in the fuse box. Older RCDs can also be found at the socket directly. Since 2010, newly installed sockets need to be protected by a RCD. But in older houses, this is not always the case. bhg Physics 3M – October 2024 49 Electric Circuit 3. Protective earth: Metallic housings of electrical devices should be connected to the ground conductor. If, for example, the line conductor comes loose and touches the housing, this produces a short circuit and a residual current at the same time (why?). This causes the circuit breaker of the RCD to trip. If the metallic housing is not grounded, it can be exposed to a voltage without anyone noticing it. If you then touch the housing, you will receive an electric shock! If a circuit breaker or the RCD has tripped, i.e. a event of excessive current or leakage current occurred, you should start to trooble shoot. Which device is responsible? You can check this, for example, by unplugging devices and then reactivating the fuse by ﬂipping the switch. If the cause is not clear or you are unsure, you should contact an electrician. 14.3.3 Exercise To which of the three safety measures (1) circuit breaker, (2) RCD or (3) protective earth do the following statements ﬁt? 1-3 answers are possible in each case. a) protects against fault current b) protects against to high currents c) diverts residual currents d) is available in every Swiss house e) is available in every new Swiss home bhg Physics 3M – October 2024 50 Electric Circuit 14.3.4 Exercise Let us go back to the example above. It considers a lamp in which the line conductor touches the (metallic) housing. What happens when you touch the housing of the lamp? Explain what happens and how dangerous the situation is for the following situations: a) The lamp is not grounded and not protected by an RCD, i.e. only by a circuit breaker. b) The lamp is again not grounded, but this time it is also protected by an RCD. c) The lamp is now grounded and protected by an RCD. d) Rate the situations. bhg Physics 3M – October 2024 51 Electric Circuit 14.3.5 Exercise Some dangerous situations are described below. Analyze them carefully: does a short circuit or residual current occur? What happens if the device is (not) grounded? How dangerous is the situation? What safety measures can be taken to protect yourself? a) Inside a television, the line conductor accidentally comes into direct contact with the neutral conductor. b) Inside a toaster the line conductor comes into contact with the (metallic) housing. c) While playing, a child inserts a metallic object into the socket. bhg Physics 3M – October 2024 52 Electric Circuit 15 Lab: Installation of a lamp bulb Goal: The aim of this lab is than you learn to connect a lamp correctly to a loose piece of cable. Material: Piece of cable, plug, lamp socket and light bulb, insulating screw joint, cable end sleeve General: Tools, RCD box Task: Take 5 minutes and discuss with your partner how to reach the goal. Make a step-by-step instruction (with some sketches) Show it to your teacher. Connect the lamp, cable and the plug. Test it at the RCD. Show it to your teacher. Product: You should have the correct step-by-step instruction at the end of the lab. bhg Physics 3M – October 2024 53 Electric Circuit bhg Physics 3M – October 2024 54

Electric Circuit 3M Physics Past Paper PDF October 2024

Document Details

Tags

Related

Summary

Full Transcript