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A-Level Physics > SAQs > Flashcards

SAQs Flashcards

1
Q

Describe what is meant by accuracy and precision (2)

A
  • Accuracy is how close a measured value is to the true value
  • Precision is the consistancy of values obtained by repeated measurements
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2
Q

The temperature of the air in a room is measured using a mercury-in-glass thermometer.
Describe how the value for the temperature may be precise but not accurate. (2)

A
  • Repeat readings can give very similar measurements so value precise
  • Value is not accurate because of a systematic error
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3
Q

“If the distance from the lens to the screen is doubled, the brightness of the image is halved.”
Assess the validity of this statement. (2)

A
  • I is proportional to 1/x2
  • So intensity fall to one quarter so statement is incorrect
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4
Q

Explain why magnetic levitation is an advantage for a high-speed transport system. (2)

A
  • Reduces frictional forces
  • Reduces work done against friction
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5
Q

Explain why the astronauts in the ISS have an apparent weight of zero. (2)

A
  • Astronauts are in free fall in the space craft
  • So there is no contact force acting on them
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6
Q

State what is meant by simple harmonic motion. (2)

A
  • Acceleration is proportional to displacement from equiolibirum position
  • and acting towards the equilibrium position
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7
Q

It is observed that electrons, with energy of 5.5 keV, are diffracted as they pass through the thin gold foil.
Explain a conclusion about the electrons that can be made from this observation. (3)

A
  • Electrons are behaving like waves
  • Wavelength = h/p
  • Electron wavlength must be similar to the atromic spacing in the foil
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8
Q

In curling:
Explain how sweeping the ice directly in front of the stone makes it travel further. (2)

A
  • Smooths out/melts the surface
  • So frictional forces are reduced
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9
Q

Explain an advantage of using a phone camera rather than a stopwatch.

A
  • Won’t be reaction time errors
  • so the uncertainty will be reduced
    OR
  • The recording can be replayed
  • this may lead to a more accurate value
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10
Q

Describe the procedure to determine an accurate value for the distance between the centres of adjacent heaps of sand. (3)

A
  • Measure over at least 3 heaps
  • Divide by the number of gaps between heaps
  • Repeat and calculate average
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11
Q

A student measured the diameter of the steel wire and obtained a value of 2.52mm.
Explain which instrument he used to measure the diameter. (2)

A
  • Micrometer Or DIGITAL calipers
  • Because the value indicates a resolution of 0.01 mm
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12
Q

Explain one advantage of locating the space station in a geostationary orbit. (2)

A
  • Satellite would always be above the same point on the Earth’s surface
  • So that contact would be maintained at all times
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13
Q

“The balance could read to the nearest 0.01g, which makes my values for the magnetic force both accurate and precise.”
Comment on this statement. (3)

A

three of four
- high precision means a small spread of values
- high accuracy means close to the true vale
- the students is referring to the resolution
- Should have said: There was a low uncertainty in the value of the force OR a high resolution doesn’t garantee accuracy/precision

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14
Q

In an A.C. circuit:
Another student suggested that a voltmeter would be more accurate than using an oscilloscope to determine the magnitude of the p.d.
Comment on this suggestion. (3)

A

three of five
- Voltmeter must measure alternating p.d.s OR voltmeter would indicate zero for a.c.
- A.C. voltmeter would give an r.m.s. p.d. directly
- Voltmeter may draw current and affect the circuit
- Accuracy would depend on the calibration of the voltmeter
- A voltmeter would give better resolution than measuring trace height on an oscilloscope

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15
Q
A
  • All stars are in the main sequence
  • In an older cluster, there would be red giants
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16
Q

When determining the period of oscillation for each mass, the student measured the time for 20 oscillations. He repeated this measurement to obtain a mean time for 20 oscillations.
Explain how the student’s procedure contributed to the accuracy of the measurement (3)

A
  • Timing a large number of oscillations minimised percentage uncertainty
  • Repeating each measurement and calculating a mean minimised the effect of random errors
  • Taking a repeat measurement allowed a check for gross timing errors
17
Q

In a diffraction experiment, the light from the laser pointer was not quite perpendicular to the screen.
Explain how this would change the diffraction pattern produced on the screen. (3)

A
  • Maxima on one side move closer to the central maximum
  • Maxima on the other side move further away from the central maximum
  • Intensity of maxima would be different on each side
18
Q

Describe how the student should determine the extension of the spring as accurately as possible. (3)

A
  • Calculate mean value of position of mass by taking loading and unloading positions of mass
  • Use a pointer on mass Or read at eye level Or Use a set square to read from metre rule Or bring metre rule as close as possible to mass
  • Check the metre rule is vertical Or fix in position
19
Q

Explain how she should have measured the thickness of the slides in order to minimise the percentage uncertainty. (2)

A
  • Measure the thickness of a stack and divide by the number of slides
  • Uncertainty would be the same, but measurement would be larger
20
Q

Assume that no energy is transferred from the chicken to the surroundings.
Explain whether the assumption is realistic. (2)

A
  • There is no way to insulate the chicken Or there will be a temperature difference with the surroundings
  • So the assumption is unrealistic
21
Q

Both microphones were initially positioned the same distance from the loudspeaker. The two signals were in phase on the oscilloscope screen. The student slowly moved microphone 2 towards the loudspeaker, until the two signals on the oscilloscope were in phase again. He then measured the distance d between the microphones to determine the wavelength λ of the sound waves.
(a) Comment on the student’s experimental technique to determine λ.

A
  • Should have moved the microphone over more in-phase positions
  • This would reduce the uncertainty
    OR
  • Move microphone between antiphase positions
  • Easier to judge when waves are in antiphase
22
Q

Explain how the principle of conservation of energy applies to the inelastic collision between a projectile and a block.

A
  • Total energy is constant, buy KE decreases
  • Projectile does work on block Or internal energy of block increases
23
Q

Part (ii)

A
  • The effective resistance of the combination is less than the lamp
  • the combination has a smaller fraction of the total resistance
  • Hence a smaller fraction of the p.d. falls across the lamp
24
Q

Criticise the method (2)

A
  • First rubber band is too near the surface
  • No method for checking the ball is at terminal velocity
25
Q
A
  • Number of charge carriers in the thermistor decreased
  • resistance of the thermistor increased
  • A larger fraction of supply p.d. is across the thermistor
26
Q

A student measured the diameter d of the wire using a micrometer.
Explain one technique the student should use when measuring d. (2)

A
  • Take readings in different positions/orientations along the wire
  • As diameter may not be uniform
    OR
  • Check for zero error
  • Zero error reduces the accuracy
27
Q

Diffraction grating experiment:
“The value of x was measured with a metre rule. A metre rule has a precision of 0.1cm, so this value was determined with a high degree of accuracy.”
Comment on this conclusion. (3)

A
  • Has a RESOLUTION of 0.1 cm (not precision)
  • Precision is how closely grouped readings are
  • Accuracy is how close the measured value is to the actual value
  • Systematic error may shift values away from the actual values (e.g. zero error or parallax)
28
Q

Battery has internal resistance.
Explain how the brightness of bulb 1 changes when the switch is closed. (3)

A
  • Current (from battery) increases
  • Therefore terminal p.d. decreases
  • so brightness of bulb 1 decreases
    OR
  • The resistance of the (external) circuit decreases
  • So there is a smaller proportion of p.d. across the bulbs
  • So brightness of bulb 1 decreases
29
Q
A
  • Ammeter should be in series with the heater
  • The range of the ammeter (mA) is too small
30
Q

Both parts

A

(i)
- Changes due to the support bending Or temperature are minimised
Or allows use of a vernier scale

(ii)
- Keep the reference wire taut/straight

31
Q

Measuring extension against force:
Explain why the test wire should be both long and thin. (3)

A
  • Thin wire has a large stress
  • A long/thin wire has a large extension
  • Hence percentage uncertainty is reduced

A-Level Physics (16 decks)

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