Page 415 - Physics Coursebook 2015 (A level)

Chapter 25: Electronics
10 In a fibre optic system, sound into a microphone is used to produce different intensities of light that are passed along the glass fibre.
The microphone is connected to a non-inverting amplifier, the output of which is connected to
an LED. An operational amplifier with dual 15 V power supplies is used as a non-inverting amplifier and the microphone produces a maximum output of +20 mV.
microphone
– +
+15 V –15 V
Figure 25.29 For End-of-chapter Question 10.
0V
a i Copy and complete the circuit in Figure 25.29 to show the resistors necessary for a non-inverting
amplifier. Make the necessary connection between the microphone and the amplifier. [2] ii Add to your diagram the necessary output components for the amplifier to work as described. [2]
b State two advantages of using negative feedback in the amplifier circuit. [2]
c i Calculate the maximum possible gain for the amplifier. [2]
ii The amplifier is used with the maximum possible gain. Suggest suitable values for the resistance of
all the resistors drawn in a i. [2]
d Explain what happens in the system when the voltage output from the microphone rises. [2]
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