A-LevelPhysicsD.C. circuits9702/43 · May/June 2018 · Q89 Marks
State what is meant by negative feedback,
- (a)(i)State what is meant by negative feedback,[2]
- (a)(ii)two effects of negative feedback on the gain of an amplifier.[2]
- (b)(i)An ideal op-amp is incorporated into the amplifier circuit shown in Fig. 8.1. [Figure 8.1] Calculate the gain G of the amplifier circuit.[2]
- (b)(ii)1.Determine the output potential difference VOUT for input potential differences VIN of -0.10 V,[1]
- (b)(ii)2.+1.3 V.[1]
- (b)(iii)The gain of the amplifier shown in Fig. 8.1 is constant. State one change that can be made to the circuit of Fig. 8.1 so that the amplifier circuit monitors light intensity levels, with the magnitude of the gain decreasing as light intensity increases.[1]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.
- [M1] (fraction of) output is combined with the input
- [A1] output (fraction) subtracted/deducted from input
- [B2] any two valid points e.g.: ∞ greater bandwidth/gain constant over a larger range of frequencies/greater bandwidth ∞ smaller gain
- [C1] gain = (-)9600/800
- [A1] =-12
- [B1] 1.2V
- [B1] -6V
- [B1] replace the 9600 Ω resistor with an LDR
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