The circuit for an inverting amplifier incorporating an ideal operational amplifier (op-amp) is shown in Fig. 7.1. [Figure 7.1]

Mark scheme

Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.

1. [1] (amplifier) gain is very large/infinite
2. [1] for amplifier not to saturate, V+ = V- or feedback (loop) ensures V+ = V-
3. [1] V+ is at earth/0 V so V-is (almost) at earth/0 V
4. [1] gain = (-)5200/800 or (−)5.2/0.80
5. [1] = -6.5
6. [1] (at saturation,) VOUT = 5 V
7. [1] p.d. across R = 5 – 2.3 = 2.7 (V)
8. [1] resistance = 2.7/(30 × 10⁻³) = 90 Ω
9. or
10. [1] Rdiode = 2.3/0.030 = 77 Ω
11. [1] Rtotal = 5.0/0.030 = 167 Ω
12. [1] Rresistor (= 167 – 77) = 90 Ω
13. or
14. [1] Rdiode = 2.3/0.030 = 77 Ω
15. [1] 77/(Rresistor + 77) × 5 = 2.3
16. [1] Rresistor = 90 Ω
17. or
18. [1] Rdiode = 2.3/0.030 = 77 Ω
19. [1] Rresistor = 77 × (2.7/2.3)
20. [1] Rresistor = 90 Ω