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2 marksElectrical Circuits

CAPE Physics Unit 2 · 2007 · Paper 2 · Question 6(b)(iii)

Figure 5 shows a seven-segment LED display and its schematic driver circuit powered by a 15 V supply. Each LED has a voltage drop of 2.0 V.

Calculate the resistance required for each of the identical protective series resistors in the display circuit.

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Other parts of this question

  1. 6(a)(i)Explain the term 'depletion region' and state how it is formed.[2 marks]
  2. 6(a)(ii)Draw a diagram showing the p-n junction under forward bias, indicate the direction of current I_D, and comment on the thickness of the depletion region.[3 marks]
  3. 6(a)(iii)Explain why a significant current flows under forward bias whereas the current is virtually zero under reverse bias.[3 marks]
  4. 6(b)(i)Identify which segments of the display must be grounded to display the digit 2.[1 mark]
  5. 6(b)(ii)If the current in each illuminated segment is 20 mA, calculate the total current drawn by the display when showing the digit 2.[2 marks]
  6. 6(c)(i)Find the peak value of the potential difference across the 1 kΩ resistor.[2 marks]
  7. 6(c)(ii)Calculate the peak value of the current I through the 1 kΩ resistor.[1 mark]
  8. 6(c)(iii)Sketch the waveforms for V_i, I, and V_R using the same time scale, with each full cycle spanning at least 8 cm on the time axis.[4 marks]

More practice: the rest of this paper · more Electrical Circuits questions · all CAPE Physics Unit 2 past papers