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A student investigated the current-potential difference relationship for a filament bulb - Edexcel - A-Level Physics - Question 16 - 2023 - Paper 2
Question 16
A student investigated the current-potential difference relationship for a filament bulb. She set up the circuit as shown. The student increased the output from the... show full transcript
Worked Solution & Example Answer:A student investigated the current-potential difference relationship for a filament bulb - Edexcel - A-Level Physics - Question 16 - 2023 - Paper 2
Step 1
Explain the shape of the graph.
Answer
The graph shows a non-linear relationship between current and potential difference.
Initially, as the potential difference increases, the current also rises gradually, indicating that the filament bulb is taking in energy and increasing its brightness. This linear portion reflects the ohmic behavior of the filament at lower voltages. As the voltage approaches a certain threshold, the rate of increase of current begins to diminish, and the graph reveals a curve. This is due to the thermal effects in the filament; as the filament heats up, its resistance also increases, leading to a smaller increase in current for a given increase in potential difference. Eventually, at higher voltages, the current begins to plateau, indicating that the filament is near its maximum operational limit and is becoming less efficient in converting electrical energy into light.
Step 2
Describe how the student could adapt her method to plot the variation of current with potential difference for the diode in forward bias.
Answer
To plot the variation of current with potential difference for the diode in forward bias, the student must make some adaptations to her experimental setup.
Firstly, she should connect a diode in the circuit, ensuring it is oriented in the forward bias direction. This is crucial because the current will only flow through the diode when it is forward biased.
Secondly, she should use a more sensitive ammeter to accurately measure lower currents that are expected at low potential differences.
Finally, the student should increase the potential difference in smaller increments, such as 0.1 V, especially around the threshold voltage (the forward voltage drop) of the diode to accurately capture the exponential increase in current typical for diodes as the potential difference surpasses this threshold. The student must also ensure to continuously record the current values for each increment of voltage to create an accurate graph.