A-LevelPhysicsD.C. circuits9702/42 · Oct/Nov 2021 · Q710 Marks
Fig. 7.1 shows an op-amp circuit that uses negative feedback. [Figure 7.1]
- (a)An operational amplifier (op-amp) has two input terminals and one output terminal. State what is meant by the gain of an op-amp.[2]
- (b)State two effects of negative feedback on the gain of an amplifier circuit that uses an op-amp.[2]
- (c)(i)State the name of the type of circuit shown in Fig. 7.1.[1]
- (c)(ii)On Fig. 7.1, label with the letter X a point in the circuit that is considered to be a virtual earth.[1]
- (c)(iii)Calculate the gain of the circuit in Fig. 7.1.[2]
- (c)(iv)Determine the value of VIN when VOUT is +6.5V.[1]
- (c)(v)Determine the value of VOUT when VIN is −5.4V.[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 (Oct/Nov 2021). The mark or mark type is shown in brackets.
- output voltage / input voltage
- input (voltage) is difference between (inverting and non-inverting) inputs
- reduces the gain
- greater bandwidth
- more stable
- inverting amplifier
- X marked anywhere between right-hand edge of 480 Ω resistor, left-hand edge of 1.2kΩ resistor and the inverting input
- gain = (-)RF / Ri
- = (-)1200/480
- = -2.5
- VIN = 6.5/(-2.5)
- = -2.6 V
- (-2.5) × (-5.4) = +13.5 V, and so output saturates
- VOUT = (+)8.0 V
Write your answer and get it marked
On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.
Sign up free →