The camera in a mobile phone uses an LED to provide light when taking a photograph - AQA - GCSE Physics Combined Science - Question 5 - 2022 - Paper 1
Question 5
The camera in a mobile phone uses an LED to provide light when taking a photograph.
A student investigated how the potential difference across an LED varies with th... show full transcript
Worked Solution & Example Answer:The camera in a mobile phone uses an LED to provide light when taking a photograph - AQA - GCSE Physics Combined Science - Question 5 - 2022 - Paper 1
Step 1
05.1 Explain how the student should have changed the circuit to make the LED emit light.
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Answer
The student should reverse the connections to the LED or battery. This is because an LED only allows current to flow in one direction, and reversing the connections will provide the correct potential difference to make it emit light.
Step 2
05.2 Calculate the potential difference across the LED.
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Answer
To find the potential difference (V) across the LED, use the formula:
V=P/I
Where:
Power (P) = 0.98 W
Current (I) = 290 ext{ mA} = 0.290 ext{ A}
Substituting in the values:
V = rac{0.98}{0.290} = 3.379
Rounded to two significant figures, the potential difference is 3.4 V.
Step 3
05.3 What happens when a xenon atom emits light?
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Answer
Electrons in the atom fall to a lower energy level.
Step 4
05.4 Calculate the mean current.
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Answer
Using the formula for current, where:
Q=Iimest
Rearranging gives:
I = rac{Q}{t}
To find charge (Q), use:
Q=1.4extJ/200extV=0.007extC
Now, substituting in the time (t = 2.8 × 10^−4 s):
I = rac{0.007}{2.8 imes 10^{-4}} = 25 ext{ A}
Therefore, the mean current is 25 A.
