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You are given an unmarked seated square box which has four identical terminals at each corner - OCR - A-Level Physics A - Question 4 - 2017 - Paper 1
Question 4
You are given an unmarked seated square box which has four identical terminals at each corner. Fig 4.1 shows the circuit diagram for the contents of the box with th... show full transcript
Worked Solution & Example Answer:You are given an unmarked seated square box which has four identical terminals at each corner - OCR - A-Level Physics A - Question 4 - 2017 - Paper 1
Step 1
Plan an experiment to determine the arrangement of the components and identify which terminal of your unmarked sealed box is A, B, C and D.
Answer
To determine the arrangement of the components, follow these steps:
- Connect the Components: Connect the 100Ω resistor across two terminals of the unmarked box (e.g., terminals A and B).
- Measure Current: Use the digital ammeter in series with the resistor to measure the current flowing through it.
- Test Other Terminals: Repeat the above steps for other combinations of terminals (C, D) or (A, C) etc.
- Observe the Results: If the current changes dramatically, one configuration likely includes a resistor. By systematically measuring and observing current at each pair of terminals, identify which pair corresponds to each resistor (220Ω and 470Ω) based on the values obtained.
Step 2
Step 3
Calculate the resistance R of the resistor for the lamp to switch on at a light intensity of 0.80 Wm^-2
Answer
From Fig. 4.3, we know that the LDR resistance at a light intensity of 0.80 Wm^-2 is approximately 3.0 kΩ.
Assuming a potential divider arrangement, we can write:
So, the resistance R of the resistor is approximately 1.0 kΩ.
Step 4
Calculate the light intensity of the surroundings at which the lamp switches off.
Answer
When V across XY is 2.4V and based on the LDR characteristics, the corresponding light intensity for this resistance (let's say approximately 2.0 kΩ) can be extrapolated from the graph in Fig. 4.3. If the graph shows that at this resistance, the light intensity is around 2.5 Wm^-2, then that is the light intensity at which the lamp switches off.