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Year 11 Physics Ohmic and Non-Ohmic Devices Aim: To investigate the voltage-current characteristics of some common circuit components A formal report is not required for this practical exercise. You are to use Crocodile Clips to construct 3 circuits, answer questions, tabulate measurements and use Excel to produce graphs. Staple the completed instruction sheets to a printout of all three circuits and the three line graphs. Make sure all sections are fully labelled, and your name is on all sheets. Write a conclusion that relates the aim to each component tested. Circuit 1: 1 Create a circuit with a battery, 2 resistors and ammeter in series. Add a voltmeter across one of the resistors. 2 Change the battery voltage (emf) from 9V to 10V by clicking on the number above the symbol and completing the resulting table as shown below left. 3 Change the resistance from 10k (10000) to 100 by clicking on the number above the symbol and completing the resulting table as shown below right. 4 Label this circuit: Circuit 1 (Resistor) by opening the Add menu and choosing Text. Type your label then drag it into place. Double click to alter the text. 5 Record the current through and the voltage across one of the resistors for a variety of batteries, eg. 10V, 8V, 6V, 4V, 2V. Voltage across Resistor V Current through Resistor I V I Note: the voltmeter and ammeter automatically change units at times so make sure you record the unit as well as the size of V and I. 6 What current would you expect to flow through the resistor when V = 0 volts?………………… Add this to your table. Maureen Trotter - Monbulk College – Year 11 Physics – Ohmic and Non-Ohmic Devices Prac 7 Two facts about V/I should be apparent from your table. What are they? ……………………………………………………………………………………………………..………... ……………………………………………………………………………………………………..………... 8 Use Excel to graph V against I (V on the vertical scale, I on the horizontal). Make sure you correctly label both axes and include a heading (eg. V-I Characteristics of a Resistor). Remember also to convert all measurements to consistent units (eg. all V or mV, not a mixture of both). 9 Is the resistor an ohmic device? …………………………………………………………………………… Explain: ………………………………………….………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… Circuit 2: 1. Create a circuit with a 10V battery, filament lamp, 100 resistor and ammeter in series. Add a voltmeter across the lamp. 2. Change the battery voltage and resistance as you did in circuit 1. 3. Label this circuit: Circuit 2 (Filament Lamp). 4. Record the current through and the voltage across the filament lamp for a variety of batteries, eg. 10V, 8V, 6V, 4V, 2V. Remember to record the unit as well as the size of V and I. 5. What current would you expect to flow through the filament lamp when V = 0 volts? …………………. Add this to your table. 6. Use Excel to graph V against I. Make sure you correctly label both axes and include a heading (eg. V-I Characteristics of a Filament Lamp). Voltage across Filament Lamp V Current through Filament Lamp I V I Remember also to convert all measurements to consistent units (eg. all V or all mV). 7. What do you notice about V/I for the filament lamp? ……………………………………………………… ……………………………………………………… 8. Is the filament lamp an ohmic device? ………………… Explain: ………………………………………….…………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… Maureen Trotter - Monbulk College – Year 11 Physics – Ohmic and Non-Ohmic Devices Prac Circuit 3: 1 Create a circuit with a 10V battery, diode, 100 resistor and ammeter in series. Add a voltmeter across the diode. Make sure that the battery and diode are facing the same way as in the circuit diagram. This ensures that the diode is forward biased. 2 Change the battery voltage and resistance as you did in circuit 1. 3 Label this circuit: Circuit 3 (Forward Biased Diode) 4 Record the current through and the voltage across the diode for a variety of batteries, eg. 10V, 8V, 6V, 4V, 2V, 1V, 0.7V, 0.5V, 0.3V, 0.1V. Remember to record the unit as well as the size of V and I. 5 What current would you expect to flow through the diode when V = 0 volts? ……………..……………. Add this to your table. 6 Use Excel to graph V against I. Make sure you correctly label both axes and include a heading (eg. V-I Characteristics of a Diode). Remember also to convert all measurements to consistent units (eg. all V or all mV). Voltage across Current through V 7 What do you notice about V/I for the diode? Diode Diode I ……………………………………………………… V I ……………………………………………………… 8 Is the diode an ohmic device? …………………….… Explain:………………………………………….…… ……………………………………………………… …………………………………..……………………… …………………………………….……………… ……………………………………………………… 9 Reverse bias the diode (replace with a diode facing the other way, or reverse the battery) 10 Label this circuit: Circuit 3 (Reverse Biased Diode) 11 Record I and V for battery voltages of: 1V, 10V, 100V, 200V, 300V, 400V. Add these results to your graph. 12 Why is it difficult to produce a V-I graph for a diode to scale? ………………………………………………………… ………………………………………………………… 13 Name a use for a diode which uses the fact that for low voltage supplies there is no current through a reversebiased diode ……………………………………………………….… Maureen Trotter - Monbulk College – Year 11 Physics – Ohmic and Non-Ohmic Devices Prac