Practical activity 2 Group work


AIM To investigate the effect of placing more resistors in parallel.


HYPOTHESIS You will write a hypothesis as part of the activity.


METHOD Step 1 Set up the circuit as for Step 1 shown in the previous activity. Step 2 Write a hypothesis and prediction for this investigation. Step 3 Name the independent and the dependent variables.


Step 4 Connect a second resistor in parallel in the circuit. Figure 3 on page 120 shows how to connect the bulbs in parallel. Observe what happens.


Step 5 Connect a third resistor in parallel in the circuit. Observe what happens.


Step 6 Unscrew one of the light bulbs and observe what happens.


RESULTS 1 Record your observations in a table as you did in Practical activity 1.


2 Explain what your observations tell you about the amount of current flowing through each resistor?


3 Explain what happens to the brightness of the bulbs if you unscrew one bulb in the circuit.


4 Predict what would happen if you unscrewed two light bulbs from the circuit.


CONCLUSION 1 Write a conclusion for this investigation about the effects of resistors in parallel circuits.


2 Use your observations in this investigation to suggest how bulbs in your home are connected. Give reasons for your answer.


DISCUSSION


When identical light bulbs (resistors) are connected in a parallel circuit, the bulbs shine just as brightly when more bulbs are added to the circuit. This means that the current increases as the number of bulbs connected in parallel increases. Each bulb gets the same amount of current as if it was connected on its own. If one of the bulbs goes out when connected in parallel, the rest of the bulbs continue to glow because the current has other pathways to flow through. The circuit is not broken.


Total: 20 marks


MATERIALS • three 1,5 V cells


• three resistors or bulbs


(3) (2)


• one switch and connecting wires


Investigate effects of more resistors in a parallel circuit


(3) (2) (2) (2)


(3) (3)


Unit 1 Series circuits and parallel circuits 121


STRAND 3


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