10.3. Potential dividers
A subsection of Physics, 9702, through 10. D.C. circuits
Listing 10 of 66 questions
A circuit incorporating an ideal operational amplifier (op-amp) is shown in . P V IN V OUT + – State the name of this circuit. Explain why the point P is referred to as a virtual earth. The circuit of is modified, as shown in . V IN 1.0 k1 C RC RB RA + – B A V The voltmeter has infinite resistance and its full-scale deflection is 1.0 V. The input potential to the circuit is VIN. The switch position may be changed in order to have different values of resistance in the circuit. The input potential VIN and the switch position are varied. For each switch position, the reading of the voltmeter is 1.0 V. Complete for the switch positions shown. switch position VIN / mV resistance A B C RA = RB = RC = 1.0 kΩ By reference to your answers in , suggest a use for the circuit of .
9702_s14_qp_41
THEORY
2014
Paper 4, Variant 1
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State the function of a comparator circuit incorporating an operational amplifier (op-amp). An ideal op-amp is incorporated into the circuit of . +1.5 V 1.2 k1 2.4 k1 +5 V R G –5 V V IN + – On , draw a circle around the part of the circuit that is being used as an output device. Show that the potential at the non-inverting input of the op-amp is 1.0 V. The variation with time t of the potential VIN at the inverting input of the op-amp is shown in . potential / V –6 –4 –2 time t t 2 t 1 +1.0 VIN 1. On the axes of , draw the variation with time t of the output potential of the op-amp. 2. State whether each diode is emitting light or is not emitting light at time t1 and at time t2. At time t1, diode R will and diode G will . At time t2, diode R will and diode G will .
9702_s14_qp_42
THEORY
2014
Paper 4, Variant 2
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A circuit incorporating an ideal operational amplifier (op-amp) is shown in . P V IN V OUT + – State the name of this circuit. Explain why the point P is referred to as a virtual earth. The circuit of is modified, as shown in . V IN 1.0 k1 C RC RB RA + – B A V The voltmeter has infinite resistance and its full-scale deflection is 1.0 V. The input potential to the circuit is VIN. The switch position may be changed in order to have different values of resistance in the circuit. The input potential VIN and the switch position are varied. For each switch position, the reading of the voltmeter is 1.0 V. Complete for the switch positions shown. switch position VIN / mV resistance A B C RA = RB = RC = 1.0 kΩ By reference to your answers in , suggest a use for the circuit of .
9702_s14_qp_43
THEORY
2014
Paper 4, Variant 3
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On , sketch the temperature characteristic of a thermistor. resistance temperature / °C A potential divider circuit is shown in . 12 V Z Y X The battery of electromotive force (e.m.f.) 12 V and negligible internal resistance is connected in series with resistors X and Y and thermistor Z. The resistance of Y is 15 kΩ and the resistance of Z at a particular temperature is 3.0 kΩ. The potential difference (p.d.) across Y is 8.0 V. Explain why the power transformed in the battery equals the total power transformed in X, Y and Z. Calculate the current in the circuit. current = A Calculate the resistance of X. resistance = Ω The temperature of Z is increased. State and explain the effect on the potential difference across Z.
9702_s15_qp_22
THEORY
2015
Paper 2, Variant 2
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An operational amplifier (op-amp) is used in the comparator circuit of . V IN V OUT 1.2 k1 4.2 k1 R –5 V +5 V +4.5 V + – Show that the potential at the inverting input of the op-amp is +1.0 V. Explain why the potential difference across resistor R is + 5 V when VIN is greater than 1.0 V and is zero when VIN is less than 1.0 V. VIN > 1.0 V: VIN The variation with time t of the input voltage VIN is shown in . 0 0 time t V IN +1 V voltage / V On the axes of , draw the variation with time t of the output potential VOUT. Suggest a use for this type of circuit.
9702_s15_qp_41
THEORY
2015
Paper 4, Variant 1
View
An operational amplifier (op-amp) is used in the comparator circuit of . V IN V OUT 1.2 k1 4.2 k1 R –5 V +5 V +4.5 V + – Show that the potential at the inverting input of the op-amp is +1.0 V. Explain why the potential difference across resistor R is + 5 V when VIN is greater than 1.0 V and is zero when VIN is less than 1.0 V. VIN > 1.0 V: VIN The variation with time t of the input voltage VIN is shown in . 0 0 time t V IN +1 V voltage / V On the axes of , draw the variation with time t of the output potential VOUT. Suggest a use for this type of circuit.
9702_s15_qp_43
THEORY
2015
Paper 4, Variant 3
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Questions Discovered
66