In this experiment you will investigate the effective resistance of different combinations of resistors and lamps in circuits. You are provided with: • power source • a switch • an ammeter • a voltmeter • three identical resistors • three identical lamps • one additional connecting lead. The supervisor has set up the apparatus as shown in Fig. 2.1. [Figure 2.1]

1. (a)(i)Close the switch. Record the potential difference V_1 across the resistors, and the current I_1 in the circuit. Open the switch. V_1 = V I_1 = A[1]
2. (a)(ii)Calculate the effective resistance R_1 of the combination of resistors using the equation: R_1 = V_1 / I_1 R_1 = Ω[1]
3. (a)(iii)Suggest why the switch is opened after the readings of potential difference and current have been taken.[1]
4. (b)Rearrange the circuit so that the resistors are connected as shown in Fig. 2.2. [Figure 2.2]
5. (b)(i)Close the switch. Record the potential difference V_2 across the resistors and the current I_2 in the circuit. Open the switch. V_2 = V I_2 = A[1]
6. (b)(ii)Calculate the effective resistance R_2 of the combination of resistors using the equation: R_2 = V_2 / I_2 Record your answer on the answer line. Write down the value of 2R_2 R_2 = Ω 2R_2 = Ω[1]
7. (c)If the resistors are identical, theory suggests that R_1 = 2R_2. Two quantities can be considered to be equal within the limits of experimental accuracy if their values are within 10% of each other. State whether your results indicate that the resistors are identical. Support your statement with a calculation. calculation statement[2]
8. (d)Set up the circuit shown in Fig. 2.1 on page 6, replacing the resistors with the lamps. Close the switch. Calculate the effective resistance R_3 of the combination of lamps. Record any readings you take and show your working. R_3 = Ω[1]
9. (e)Rearrange the circuit as shown in Fig. 2.2 on page 7, replacing the resistors with the lamps. Close the switch. Calculate the effective resistance R_4 of the combination of lamps. Record any readings you take and show your working. R_4 = Ω[1]
10. (f)The teacher explains that the resistance of the lamp filaments changes due to a heating effect and therefore R_3 is not equal to 2R_4. Describe one observation that you made while doing the experiment that supports the teacher's explanation.[1]

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