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A student investigates the current–potential difference characteristics of a diode - OCR Gateway - GCSE Physics - Question 19 - 2023 - Paper 3

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A student investigates the current–potential difference characteristics of a diode. Fig. 19.1 shows the circuit diagram the student sets up to measure the current i... show full transcript

Worked Solution & Example Answer:A student investigates the current–potential difference characteristics of a diode - OCR Gateway - GCSE Physics - Question 19 - 2023 - Paper 3

Step 1

Mistake 1

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Answer

The student may have connected the diode in reverse bias instead of forward bias. To correct this, ensure that the anode of the diode is connected to the positive terminal of the power supply and the cathode to the negative terminal.

Step 2

Correction 1

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Answer

Verify that the connections are correct to ensure proper current flow through the diode.

Step 3

Mistake 2

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Answer

The student may have incorrectly set the ammeter in series. The ammeter needs to be connected in series with the diode to measure current accurately. If it was connected in parallel, this would create a short circuit.

Step 4

Correction 2

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Answer

Disconnect the ammeter from its current position and re-connect it in series with the diode.

Step 5

State the potential difference when the diode starts to conduct.

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Answer

The potential difference when the diode starts to conduct is approximately 0.7 V, as indicated in Fig. 19.2.

Step 6

Use the gradient of the graph to calculate a value for the resistance of the diode when it is conducting.

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Answer

To find the resistance, calculate the gradient of the linear portion of the graph. Suppose the two points used are (1, 0.05) and (2, 0.1). The gradient, which represents the change in current over the change in voltage, is:

Gradient=0.1−0.052−1=0.05 A/V\text{Gradient} = \frac{0.1 - 0.05}{2 - 1} = 0.05 \text{ A/V}

Using Ohm's Law, resistance is given by:

R=VI=0.70.05=14ΩR = \frac{V}{I} = \frac{0.7}{0.05} = 14 \Omega

Thus, the resistance of the diode when conducting is 14 Ω.

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