Section II
Question 32 - 2002 HSC
(a) Describe the structure of an light emitting diode (LED). Explain why it is sometimes preferable to use an LED rather than an ordinary light source. (b) Using a diagram, describe qualitatively how the resistance of an light dependent reistor (LDR) changes as the illumination increases. Calculate the resistance of the LDR for a given intensity of light. Calculate the resistance of the coil of a relay when it connected in series with the LDR and a 12volt power supply. (c) Describe the properties of an ideal amplifier. Given a table of output and input voltages of an amplifier, calculate its gain. Propose why the amplifier is not suitable for input signals that vary
from −250 to +250 microvolt. (d) Discuss the impact and limitations on computers of changing from thermionic devices to transistors to integrated circuits.
