9.3. Resistance and resistivity
A subsection of Physics, 9702, through 9. Electricity
Listing 10 of 234 questions
White light passes through a cloud of cool low-pressure gas, as illustrated in . white light emergent light cool gas For light that has passed through the gas, its continuous spectrum is seen to contain a number of darker lines. Use the concept of discrete electron energy levels to explain the existence of these darker lines. The uppermost electron energy bands in a solid are illustrated in . conduction band (CB) forbidden band (FB) valence band (VB) Use band theory to explain the dependence on light intensity of the resistance of a light-dependent resistor (LDR).
9702_s20_qp_41
THEORY
2020
Paper 4, Variant 1
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White light passes through a cloud of cool low-pressure gas, as illustrated in . white light emergent light cool gas For light that has passed through the gas, its continuous spectrum is seen to contain a number of darker lines. Use the concept of discrete electron energy levels to explain the existence of these darker lines. The uppermost electron energy bands in a solid are illustrated in . conduction band (CB) forbidden band (FB) valence band (VB) Use band theory to explain the dependence on light intensity of the resistance of a light-dependent resistor (LDR).
9702_s20_qp_43
THEORY
2020
Paper 4, Variant 3
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10 The circuit for an amplifier incorporating an ideal operational amplifier (op-amp) is shown in . – + +9 V P R2 –9 V R1 VIN VOUT State 1. the name of this type of amplifier circuit, 2. why the point P is referred to as a virtual earth. Show that the gain G of this amplifier circuit is given by the expression G = – R2 ––– R1 . Explain your working. The circuit of is modified by connecting a light-dependent resistor (LDR) as shown in . – + +9 V R2 –9 V R1 VIN VOUT = +1.2 V V The resistances R1 and R2 are 5.0 kΩ and 50 kΩ respectively. The input voltage VIN is +1.2 V. A high-resistance voltmeter measures the output VOUT. The circuit is used to monitor low light intensities. Determine the voltmeter reading for light intensities such that the LDR has a resistance of 1. 100 kΩ, reading = V 2. 10 kΩ. reading = V The light incident on the LDR is provided by a single lamp. Use your answers in to describe and explain qualitatively the variation of the voltmeter reading as the lamp is moved away from the LDR.
9702_w08_qp_4
THEORY
2008
Paper 4, Variant 0
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The resistance of a thermistor at 0 °C is 3840 Ω. At 100 °C the resistance is 190 Ω. When the thermistor is placed in water at a particular constant temperature, its resistance is 2300 Ω. Assuming that the resistance of the thermistor varies linearly with temperature, calculate the temperature of the water. temperature = °C The temperature of the water, as measured on the thermodynamic scale of temperature, is 286 K. By reference to what is meant by the thermodynamic scale of temperature, comment on your answer in . A polystyrene cup contains a mass of 95 g of water at 28 °C. A cube of ice of mass 12 g is put into the water. Initially, the ice is at 0 °C. The water, of specific heat capacity 4.2 × 103 J kg–1 K–1, is stirred until all the ice melts. Assuming that the cup has negligible mass and that there is no heat exchange with the atmosphere, calculate the final temperature of the water. The specific latent heat of fusion of ice is 3.3 × 105 J kg–1. temperature = °C
9702_s10_qp_42
THEORY
2010
Paper 4, Variant 2
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The resistance of a thermistor at 0 °C is 3840 Ω. At 100 °C the resistance is 190 Ω. When the thermistor is placed in water at a particular constant temperature, its resistance is 2300 Ω. Assuming that the resistance of the thermistor varies linearly with temperature, calculate the temperature of the water. temperature = °C The temperature of the water, as measured on the thermodynamic scale of temperature, is 286 K. By reference to what is meant by the thermodynamic scale of temperature, comment on your answer in . A polystyrene cup contains a mass of 95 g of water at 28 °C. A cube of ice of mass 12 g is put into the water. Initially, the ice is at 0 °C. The water, of specific heat capacity 4.2 × 103 J kg–1 K–1, is stirred until all the ice melts. Assuming that the cup has negligible mass and that there is no heat exchange with the atmosphere, calculate the final temperature of the water. The specific latent heat of fusion of ice is 3.3 × 105 J kg–1. temperature = °C
9702_s10_qp_43
THEORY
2010
Paper 4, Variant 3
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An operational amplifier (op-amp) may be used as a comparator. State the function of a comparator. The variation with temperature θ of the resistance R of a thermistor is shown in . 1.0 2.0 3.0 4.0 R / kΩ θ / °C The thermistor is connected into the circuit of . +5V +9V + – –9V 2.0kΩ 2.0kΩ V OUT X The op-amp may be considered to be ideal. The temperature of the thermistor is 10 °C. Determine the resistance of the variable resistor X such that the output potential VOUT is zero. resistance = Ω The resistance of the resistor X is now held constant at the value calculated in . Describe the change in the output potential VOUT as the temperature of the thermistor is changed from 5 °C to 20 °C.
9702_s11_qp_41
THEORY
2011
Paper 4, Variant 1
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Two properties of an ideal operational amplifier (op-amp) are infinite input impedance and infinite bandwidth. State what is meant by: infinite input impedance infinite bandwidth. A student uses a negative temperature coefficient thermistor in the circuit of to indicate changes in temperature. 1.5 V +5.0 V –5.0 V – + V 1100 Ω 96 kΩ 100 kΩ 400 Ω X Show that the potential at point X is 0.40 V. The thermistor has a resistance of 360 kΩ at a particular temperature. For this temperature of the thermistor, calculate the magnitude of the reading on the voltmeter. voltmeter reading = V The temperature of the thermistor increases. State and explain the effect of this change on the magnitude of the reading on the voltmeter. Explain why the amplifier circuit will no longer indicate temperature changes when the magnitude of the gain of the circuit is greater than 12.5.
9702_s21_qp_42
THEORY
2021
Paper 4, Variant 2
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Questions Discovered
234