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A Level Physics > Module 4 PAGs > Flashcards

Module 4 PAGs Flashcards

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1
Q

How does the resistance of a NTC thermistor vary with temperature?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

As temperature increases, the resistance of the NTC thermistor will decrease

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1
Q

Why should you avoid heating the water too quickly?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

The thermistor and thermometer will have thermal inertia. If you try to heat the water too quickly, the temperature of the thermistor and thermometer won’t be the same as that of the water.

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2
Q

What is the advantage of heating the water very slowly when carrying out this experiment?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

By heating the water very slowly, you are allowing the thermistor and thermometer to become as close in temperature to the water as possible.

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3
Q

What safety precautions should be taken when using a bunsen burner?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

● Hair and loose clothing should be tied back
● A heatproof mat should be used to protect the work bench
● The safety flame should be used when not directly heating the water
● Avoid touching metal regions near the flame

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4
Q

What is the added risk when using wires near a bunsen burner

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

You must ensure that the wires don’t get caught on the bunsen burner or touch any hot components.

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5
Q

What does a potential divider do?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

A potential divider is an arrangement that allows a desired output voltage to be produced by producing the required ratio of resistances.

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6
Q

How could you cool the thermistor down to zero degrees in this experiment?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

The experiment can start with the thermistor placed in a beaker of ice. This can then be heated using a bunsen burner to produce resistance measurements from 0°C right up to 100°C.

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7
Q

What should you do when you add hot water to ensure the temperature is constant throughout?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

You should use a stirrer to stir the water before taking temperature readings.

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8
Q

How should you take a reading from a thermometer?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

Thermometer readings should be taken at eye level to reduce parallax errors.

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9
Q

What graph could be plotted to obtain a calibration curve for temperature?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

A graph of the output potential difference against temperature could be plotted. A curve of best fit can then be drawn in and this can be used as a calibration curve.

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10
Q

How does the resistance of an LDR vary with light intensity?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

The resistance of an LDR increases as the light intensity decreases.

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11
Q

How can light intensity be measured?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

Light intensity can be measured using a digital light sensor.

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12
Q

Why is it important that the fixed resistor value isn’t too high?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

If the fixed resistor is significantly larger than the thermistor resistance, changes in temperature won’t result in a significant enough change in the output voltage. This will make it harder to measure how the output changes.

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13
Q

Why is it important that the fixed resistor value isn’t too low?

PAG 04.3 - Using Non-Ohmic Devices as Sensors

A

If the fixed resistor value is too low, it may result in the output voltage changing across too big a range of values. This range may exceed the range measurable using a voltmeter.

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14
Q

State the equation used to calculate the resistivity of a wire.

PAG 03.1 - Determination of Resistivity

A
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15
Q

How does the resistance of a wire change when the cross-sectional area decreases?

PAG 03.1 - Determination of Resistivity

A

The resistance of a wire is inversely proportional to the cross-sectional and so as the area decreases, the resistance will increase.

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16
Q

How does the resistance of a wire change when the length is decreased?

PAG 03.1 - Determination of Resistivity

A

The resistance of a wire directly proportional to the length of the wire, so as the length decreases the resistance also decreases.

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17
Q

How does the resistance of a wire change if the resistivity is increased?

PAG 03.1 - Determination of Resistivity

A

The resistance of a wire is directly proportional to the resistivity, so as the resistivity increases, the resistance also increases.

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18
Q

What is the unit of resistivity?

PAG 03.1 - Determination of Resistivity

A

Ωm

Ohm - Metre

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19
Q

How do you measure the cross-sectional area of a thin wire?

PAG 03.1 - Determination of Resistivity

A

Using a micrometer, measure the wire’s diameter in at least three different places along the wire. Use the average diameter in the circular area equation.

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20
Q

Suggest how the length of conducting wire can be varied when carrying out this experiment.

PAG 03.1 - Determination of Resistivity

A

One end of the wire can be fixed and the other end can be connected to the circuit using a crocodile clip. The length of conducting wire can be changed by varying the position of the crocodile clip.

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21
Q

Describe how the length of the wire should be measured.

PAG 03.1 - Determination of Resistivity

A

The length of the wire should be measured by a metre ruler, with the wire held taught. This reduces the likelihood of an incorrect measurement due to kinks in the wire.

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22
Q

What device is used to measure the potential difference across the wire, and how is it connected?

PAG 03.1 - Determination of Resistivity

A

A voltmeter should be connected in parallel across the wire.

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23
Q

What device is used to measure the current flowing through the wire, and how is it connected?

PAG 03.1 - Determination of Resistivity

A

An ammeter should be connected in series with the wire.

24
Q

Why should the power supply be switched off between readings?

PAG 03.1 - Determination of Resistivity

A

The temperature of the wire should remain constant throughout the experiment. Switching the power supply off between readings will reduce the heating of the wire.

25
Q

Why should the temperature of the wire remain constant throughout this experiment?

PAG 03.1 - Determination of Resistivity

A

Temperature changes can affect the resistance of the wire. In this experiment, temperature is a control variable.

26
Q

Why does the resistance of a wire increase when its temperature increases?

PAG 03.1 - Determination of Resistivity

A

As temperature increases, the metal ions gain more kinetic energy and so vibrate more. These vibrating ions make it harder for charges to pass through the wire and so the wire’s resistance increases.

27
Q

How can the resistivity of a wire be determined from a graph of resistance against length?

PAG 03.1 - Determination of Resistivity

A

The gradient of the graph will be R/L and so by multiplying the gradient by the wire’s cross-sectional area, you will obtain the wire’s resistivity.

28
Q

Why should the current used in this experiment be kept low?

PAG 03.1 - Determination of Resistivity

A

As current increases, the temperature of the wire will increase. By keeping the current low, the heating effect is kept to a minimum.

29
Q

Suggest how you could ensure that your length measurements are taken from the same position each time.

PAG 03.1 - Determination of Resistivity

A

A metre ruler could be taped in place below the fixed wire.

30
Q

What factors lead to uncertainties in this experiment?

PAG 03.1 - Determination of Resistivity

A

There will be resistance between the crocodile clips and wire as well as at the contact of the leads and the power supply. There may also be a zero error due to the positioning of the ruler and crocodile clip at the zero end.

31
Q

What device could replace the voltmeter and ammeter in this experiment?

PAG 03.1 - Determination of Resistivity

A

Instead of a voltmeter and ammeter, a multimeter could be used to measure the current and potential difference.

Note that this may lower the resolution of your data depending on the number of significant figures provided by the devices you have available.

32
Q

How can the percentage difference in your experimental value and accepted value be calculated?

PAG 03.1 - Determination of Resistivity

A

[(Your Value - Accepted Value)/Accepted Value] x 100%

33
Q

Does the resistivity of a material change depending on dimensions?

PAG 03.1 - Determination of Resistivity

A

Resistivity is a material property and so is fixed for a given material, regardless of dimensions.

34
Q

What forms at the closed end of a tube when a stationary wave is formed?

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tube

A

When a stationary wave is formed in a tube, a node will form at the closed end.

35
Q

What is a node?

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tube

A

A node is a point on a stationary wave where there is zero displacement.

36
Q

What forms at the open end of a tube when a stationary wave is formed?

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tube

A

When a stationary wave is formed in a tube, an antinode will form at the open end.

37
Q

Describe the waveform of a stationary wave at its fundamental frequency in a tube with an open and closed end.

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tube

A

When oscillating at its fundamental frequency, there will be one node at the closed end and one antinode at the open end.

38
Q

What must the length of the resonance tube be for it to resonate at the fundamental frequency?

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tube

A

The length of the tube must be one quarter of the wavelength of the sound.

39
Q

How can wave speed be calculated from frequency and wavelength?

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tube

A

Wave Speed = Wavelength x Frequency

40
Q

How do you know when the tube is resonating?

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tube

A

The sound will be at its loudest when the tube is undergoing resonance.

41
Q

What is the general form of the tube length required for resonance to occur?

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tube

A
Where n = 0, 1, 2, 3 …
42
Q

What is the speed of sound in air?

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tube

A

The speed of sound in air is around 340m/s.

43
Q

How can the mean wavelength be calculated?

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tub

A

Calculate the wavelength of the sound using as many resonant lengths as possible. Sum these values and divide by the number of wavelengths used to produce the mean wavelength.

44
Q

Why must the external temperature remain constant in this experiment?

PAG 05.2 - Determining the Speed of Sound Using a Resonant Tub

A

The speed of sound can vary with the temperature of the air.

45
Q

Describe the I-V characteristic for an LED.

PAG 06.1 - Determining the Planck Constant

A

An LED is a light-emitting diode and so current can only pass through it in one direction. It also requires a minimum voltage (threshold voltage) before current can flow.

46
Q

What is a threshold voltage?

PAG 06.1 - Determining the Planck Constant

A

A threshold voltage is the minimum potential difference that needs to be across a diode before it allows a current to flow

47
Q

How can the threshold voltage be obtained experimentally?

PAG 06.1 - Determining the Planck Constant

A

Slowly increase the potential difference across the LED until it just begins to emit light, and current flows through it. The value at which this occurs is the threshold voltage.

48
Q

How can you determine the point at which the LED begins to glow more precisely?

PAG 06.1 - Determining the Planck Constant

A

The LED can be viewed through a matt black paper tube to help prevent external light interfering with you view.

49
Q

How could you vary the potential difference across the LED without altering the power supply?

PAG 06.1 - Determining the Planck Constant

A

The LED can be placed in a potential divider circuit with a rheostat. As the resistance of the rheostat decreases, the potential difference across the LED will increase.

50
Q

What device can be used to measure the potential difference across the LED?

PAG 06.1 - Determining the Planck Constant

A

A voltmeter connected in parallel to the LED will measure the potential difference across it.

51
Q

How can the energy of a photon be obtained from its frequency?

PAG 06.1 - Determining the Planck Constant

A

Energy = Planck’s Constant x Frequency
E = hf

52
Q

How can the energy of a photon be obtained from its wavelength?

PAG 06.1 - Determining the Planck Constant

A

Energy = (Planck’s Constant x Speed of Light) / Wavelength
E = hc/λ

53
Q

What is the minimum energy of an electron moving through a potential difference?

PAG 06.1 - Determining the Planck Constant

A

Energy = Charge of Electron x Potential Difference
E = eV

54
Q

What equation can be formed by equating the electron energy and photon energy?

PAG 06.1 - Determining the Planck Constant

A

eV = hc/λ

55
Q

Is the wavelength of a green photon larger or smaller than the wavelength of a red photon?

PAG 06.1 - Determining the Planck Constant

A

Red photons have a larger wavelength than green photons. This means the red photons have a smaller energy.

56
Q

How can the Planck constant be determined from a graph of threshold voltage against 1/λ?

PAG 06.1 - Determining the Planck Constant

A

The gradient of the graph will be Vλ.
Vλ = hc/e (rearranged energy balance)
Therefore the Planck constant is given by e/c multiplied by the gradient.

57
Q

How can the percentage difference in your experimental value and accepted value be calculated?

PAG 06.1 - Determining the Planck Constant

A

[(Your Value - Accepted Value)/Accepted Value] x 100%

58
Q

What safety precautions should be taken when carrying out this experiment?

PAG 06.1 - Determining the Planck Constant

A

Ensure that the currents passing through the LEDs don’t exceed their current ratings. Avoid touching any bare metal contacts and handle the components with care since they may become hot.

A Level Physics (31 decks)

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