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Transcript
Ohm’s Law and Basic Circuit Theory – Answer Sheet Ohm’s Law: Q1) On your worksheet sketch the circuit. Set the resistance to 140 ohms. Complete the table on your worksheet. As you increase the voltage the number of batteries will increase in 1.5-volt increments. Note hat the simulation shows current flow not electron flow. Current flows from positive to negative and the electrons flow from negative to positive. Current flow is an historical aberration. There is no physical material flowing as is shown for the current. What is really occurring is an electron flow. Nevertheless current flow is still spoken of. Place sketch here: Resistance (Ohms) 140 140 140 140 140 140 Voltage (Volts) 1.5 3.0 4.5 6.0 7.5 9.0 Current (milliamps) Q2) Complete the following statement; as the voltage across the resistor is doubled the current that flows through the resistor is ... Q3) What did you notice about the physical size of the V and the I in the equation as this increase in voltage occurred Q4) What therefore can be said about the relationship between current and voltage given a constant resistance value in the circuit as shown? Q5) Using the data from the table above open an Excel spreadsheet and copy the data for voltage and current into the spreadsheet. Plot the voltage on the y-axis and the current on the x-axis. Make sure you use a scatter plot. Add a trend line to the graph that is plotted and make sure that you display the equation of the line on the graph. Q6) What is the equation of this line and what is its significance? Q7) Set the voltage to 4.5 volts and change the resistance in increments of 100 ohms. Remember that the voltage that is supplied by the batteries is then applied across the resistor. Complete the following table. Voltage (volts) 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 Resistance (Ohms) 100 200 300 400 500 600 700 800 900 1000 Current (mA) Q8) What conclusion can be drawn regarding the current that flows in a circuit as the resistance is increased with constant voltage applied. Be specific with your answer. Q9) The equation for Ohm’s Law can be written in three different forms each with a different quantity as the subject of the equation. Write each of these in the space provided. Q10) Write a word statement summarising Ohm’s Law by completing the following statement: The current that flows through a resistor in a circuit is ....... Circuit Theory: a) Using Voltmeters and Ammeters: Q11) What values are displayed on the voltmeter and the ammeter? Remember voltmeters measure energy difference of the electrons between two points and ammeters measure current or electron flow. Q12) The voltmeter placed as it was is essentially part of the circuit. Electrons must therefore pass through the voltmeter. What conclusion can be drawn about placing voltmeters in circuits in this fashion with respect to the circuit’s ability to allow electron flow? Attach the voltage probes to positions A and B. Close the switch. Click the Show Values dialog box. Record the values in the table. Device Measurement (add appropriate units for each measurement) Ammeter Light Globe Voltmeter Battery Switch Q13) The battery increases the energy of the electrons. Given that 1-volt represents an energy gain of 1 joule per coulomb what energy gain does this battery supply? Q14) The light bulb uses the energy of the electrons. What energy loss does the light bulb produce in the electrons? Q15) The resistance of the switch is stated as zero ohms. Connect the voltmeter across the switch. How much energy is lost per coulomb of electrons as they pass through the switch. Q16) Determine the current flowing through the light bulb by using the appropriate form of the Ohm’s Law equation. How does the value that you calculated compare to the value as shown on the simulation? Q17) Measure the voltage across the each light globe and then across the two light globes. Record the values in the table. Voltage Voltage across A only Voltage across B only Voltage across AB Q18) Summarise the results above. Q19) The brightness of the bulb is shown by yellow lines surrounding it. Compare the brightness of the bulb(s) when the circuit has one bulb and when it has two bulbs.