PHYSICS UNIT 3

Question 1

meter ruler

Answer 1

Parallax error when measuring the height of the bulb/lens with the
ruler
* Use a set square from rule to bulb/lens
* Metre rule not vertical
* Use a set square to ensure metre rule is perpendicular to the
base/paper
* Zero error when measuring the height from the lens to the bulb
* Check zero on the rule is aligned with top of the liquid
* Filament sealed within glass, so cannot measure distance directly
* Measure to the middle of the bulb

Question 2

critising

Answer 2

• No repeat measurements
• Inconsistent d.p. for d
  Inconsistent number of significant figures (for wavelength)
• Only 5 sets of results
• Range of values of angle/wavelength is too small
• No evidence of repeat
  Mass is not measured to the nearest gram
  Or mass is not measured (in kg) to 3 d.p.
• Inconsistent/incorrect number of significant figures for GPE
• Mean energy supplied values should be 3 s.f. (to match measured
  values) (Accept 2 d.p.)
• Too few readings
• Too small a range of temperatures
• Inconsistent intervals in temperature readings
• Inconsistent d.p. in current values

Question 3

glass

Answer 3

Glass is brittle, so will snap/break
* Sharp edges could cause injury by causing cuts
* Glass is stiffer, so a larger force/mass would be needed
* A large mass could cause injury if the mass falls on feet

Question 4

Describe an experimental method to determine the value of ș at which d is a maximum.

Answer 4

Measure the distance at which the plastic sphere lands with a ruler
Or measure the launch angle with a protractor
* Repeat measurements (for each angle) and calculate the mean d
* Plot a graph of d and θ, and use to find θ for maximum d value
Or continue changingθ until d decreases to find maximum
* Around the maximum d take measurements for smaller changes in angle

Question 5

Explain why taking further readings could improve the accuracy of his value for the
terminal p.d. of the cell.

Answer 5

Further readings would make the line of best fit more accurate
* Giving a more accurate value for the p.d. of the rod (at 30cm)

Question 6

Explain why the polarimeter light source should have a low power.

Answer 6

Higher power lamp would have a heating effect on the solution
Or Higher power lamp would increase the temperature of the solution
* Heating would cause expansion of the sucrose solution
Or heating would cause evaporation of the sucrose solution
* Which would change the concentration/density (of sucrose solution)

Question 7

The metal surface in this apparatus can be used to determine the Planck constant with
visible light. Other metals require higher photon energies.
Explain an advantage

Answer 7

Higher photon energy means higher frequency light
Or higher photon energy means using ultraviolet light
* There is an increased risk when using ultraviolet light
Or using visible light is no/low ris

Question 8

) Suggest two modifications that would improve the accuracy of the value of the Planck
constant determined from this experimen

Answer 8

Block out external light sources
* Use a larger range of wavelengths/frequencies
* Use filters with a narrower frequency band
* Use LEDs of known frequency
* Use more sensitive ammeter

Question 9

Explain why this micrometer is suitable to measure the diameter of the metal sphere.

Answer 9

Percentage uncertainty is small
* Because resolution much less than diameter of ball bearing

Question 10

Describe how the student should use this measuring device to make the
measurements as accurate as possible.

Answer 10

Take readings in different orientations/positions
* Check for zero error
* Ensure measurement is at widest point

Question 11

Describe what the student should do to obtain the data to plot the force-extension graph.

Answer 11

Reference to Force = mg
Or reference to use of a Newtonmeter to measure weight
* Measure initial length of spring and length with load, and subtract to give
extension
Or align zero on ruler to bottom end of spring and read opposite bottom
when loaded to measure extension
Or read scale opposite bottom of spring initially and again with load, and
subtract to get extension
* Use of a set square to ensure the ruler is vertical
Or use of a set square to reduce parallax error when measuring
length/extension
Or use of a pointer attached to the lower end of spring to reduce parallax
error when measuring length/extension
Or ensure ruler and spring are at eye-level to reduce parallax
* Uses a range of masses/forces to obtain multiple pairs of values

Question 12

) Explain how you would use the graph to determine the stiffness of the spring

Answer 12

k = gradient
Or k = ΔF/Δx
* Gradient should be calculated using values from linear section of the graph

Question 13

Describe how the student can accurately determine the radius of the first bright ring
of the diffraction pattern.

Answer 13

• Use of Vernier calipers
  Or use of dividers/calipers to transfer the measurement to a ruler
  Or use of paper (tape) and marking points to be measured with a ruler
  Or use a flexible measuring tape
• Measure diameter of (first) ring and divide by 2
• Measure in multiple orientations and calculate the mean
• Measure to the middle/brightest part of the ring

Question 14

how electrons hsow wave property

Answer 14

(Diffracted) electrons experience (constructive) interference/superposition
Or the pattern is evidence electrons have interfered/superposed
* Diffraction/interference is a wave property

Question 15

A student carried out an experiment to determine the mass per unit length μ of a string,
using a standing wave. Identify two significant sources of uncertainty in the student’s measurements.
(

Answer 15

Frequency
* Uncertainty in identifying when nodes form
* Uncertainty in identifying maximum amplitude
Length
* Parallax error when measuring length
* Uncertainty in measuring length to top of pulley
Or uncertainty in measuring length as string is not straight
Mass
* Zero error on mass balance

Question 16

) For each of these sources of uncertainty, describe an experimental technique the
student could have used to obtain an accurate measurement.

Answer 16

Examples
Frequency
* Repeat and calculate the mean frequency
* Vary frequency from above and below resonance to find two values for the
frequency when the standing wave forms
Length
* Use a set square to reduce parallax error in length
Or hold ruler in contact with the wire to reduce parallax error in length
Or ensure ruler and string are at eye-level
* Switch off vibrator
Or ensure string is straight
Mass
* Zero balance before each measurement
* To remove systematic error
Or idea that this error is not reduced by repeating

Question 17

A student was asked to investigate how changing the temperature of a diode will change
the potential difference at which the diode starts to conduct.Identify one safety issue with this investigation and how it may be dealt with.

Answer 17

Risk of scalding from hot water
* Clamp beaker
* Risk of burns from hot apparatus
* Wear gloves
* Risk of electric shock from power supply
* Keep separate from water bath
Or Use a low voltage power supply

Question 18

Describe a method the student could use to determine the density of the salt solution.

Answer 18

Mass (of solution) obtained using a (top pan) balance
* Volume (of solution) measured with a measuring cylinder
* Calculate density = mass / volume

Question 19

The relationship between the refractive index n, the angle of incidence θ1
and the
angle of refraction θ2
is given by the equation
sin θ1
= n sin θ2
Describe a graphical method she could use to determine n.

Answer 19

Measure θ2 for different θ1
* Measure at least 5 pairs of angles
* Plot graph of sin θ1 against sin θ2
* Refractive index is the gradient of the line

Question 20

The students repeated the experiment with a much larger mass and determined that
the efficiency of the motor was decreased.
Describe how they should collect and use data to determine the mass at which the
efficiency starts to decrease

Answer 20

Continue increasing the mass and extend the graph
* Identify the mass/point at which the line starts to curve
* Take smaller increments in mass around this point
Using larger masses, calculate the efficiency (using efficiency = mgh
÷ mean energy supplied) and plot a graph of efficiency against mass
* Identify the mass/point where the graph peaks
Or identify the mass where efficiency starts to decrease
* Take smaller increments in mass around this point

Question 21

) Describe how the same apparatus could be used to calculate a more accurate
value for the rate of flow of the oil.

Answer 21

Starting timer after oil has been poured
e.g. marking a start position, starting at 10 cm3
* Stopping timer before the funnel is empty
e.g. stopping after a fixed volume or at a marker
* Record the volume after a fixed time period
* Repeat for the same temperature and calculate the mean time
* Use of light gates and (electronic) timer to avoid (human) reaction
time

Question 22

The accuracy of the value of the Planck constant calculated depends on the minimum p.d.
determined from the graph.
Explain how the student could reduce the uncertainty in her value of the minimum p.d

Answer 22

There would be an uncertainty in wavelength/frequency
Or there would be a range of wavelengths/frequencies
Or the LED emits different wavelengths/frequencies
* If wavelength was longer, the calculated Planck constant would be
larger
Or if the frequency was lower, the calculated Planck constant would
be larger
* There would be an uncertainty in the calculated Planck constant
Or there would be a range of possible values of the Planck constan

Question 23

Describe how the student could ensure that the intensity of light incident on the solar
cell remained constant

Answer 23

Same distance between lamp and solar cell
* Keep angle of solar cell to light the same
* Block background light
Or control background light level
Or avoid casting shadows on the solar cell

Question 24

A tyre manufacturer carries out similar tests on samples of the rubber used for tyres.
Suggest why these tests are necessary

Answer 24

To test tyres would provide enough friction/braking force
Or to test tyres provide enough grip
Or to test the rubber on wet/icy/cold/loose surface materials
* So that the tyres can stop the car in a safe distance/time
Or to prevent cars from skidding/sliding

Question 25

Explain why using monochromatic light would increase the validity of the conclusion made in (c).

Answer 25

The monochromatic light has a single wavelength/frequency Or White light is a mixture/range of wavelengths/frequencies * The different wavelengths/colours would refract by different angles Or different wavelengths/colours would have different refractive indexes * Monochromatic light would give less uncertainty in the angle (incident/refraction/critical) Or monochromatic light allows for a more accurate measurement of angle

Question 26

A student took measurements to plot a force-extension graph for a rubber band. (a) Describe a method he could have used to take the measurements. Your answer should include a diagram.

Answer 26

Diagram showing rubber band suspended/clamped at one end (e.g. hanging from a clamp stand) * Force applied to band (e.g. slotted masses hanging on free end) * Measure initial length using a ruler Or mark position of bottom of band on ruler * Measure new length/position and calculate extension * Additional detail to improve accuracy e.g. method for reducing parallax Or additional detail to improve safety e.g. ensure feet are not under the masses in case they fall

Question 27

Discuss the advantages of choosing the digital multimeter to measure the potential difference.

Answer 27

(Percentage) uncertainty will be reduced * The multimeter screen/display will not cause a parallax error * The multimeter can measure to a higher resolution Or the multimeter resolution can be increased by changing the setting Or the multimeter measures to 2 d.p. * The digital multimeter will not require interpolation of values

Question 28

Explain one modification to this investigation that would improve the accuracy of the values of R0 and α determined in (c)A student investigated how changing the temperature of a copper wire affects the resistance of the wire.

Answer 28

Take a resistance measurement at 0 ˚C * to measure R0 accurately * Take resistance measurements for lower temperatures * to improve the accuracy of the gradient Or to improve the accuracy of the y-axis intercept * Take resistance measurements for smaller increments of temperature * to improve the accuracy of the gradient Or to improve the accuracy of the y-axis intercept * Take resistance measurements for a wider range of temperatures * to improve the accuracy of the gradient Or to improve the accuracy of the y-axis intercept * Stir the water regularly Or place the thermometer inside the copper coil * so the temperature of water plotted is the same as the temperature of the copper * Use a datalogger to measure temperature and resistance * so that the values are recorded simultaneously * Use a digital thermometer * to avoid parallax error Ignore higher resolution for a digital thermometer.

Question 29

Explain why using thicker sheets of acetate would reduce the uncertainty in her value for density.

Answer 29

(Absolute) uncertainty would stay the same Or resolution of the measuring device is the same * So, percentage uncertainty in thickness/mass would reduce

Question 30

one precaution that should be taken before using a micrometer.

Answer 30

zero error

Question 31

Describe a method to determine the maximum force the nylon fishing line can withstand before breaking

Answer 31

Sample of nylon secured at one end * Slotted masses hung from the opposite end * Force/mass increased until sample breaks * F = mg to calculate the force Or use a force meter to measure the weight of the mass

Question 32

safety issue

Answer 32

amples * Masses falling on feet * Ensure feet are not underneath * Snapped nylon hitting eyes * Wear safety glasses

Question 33

Explain how friction between the cube and the surface of the ramp would affect the value obtained for e.

Answer 33

friction would reduce velocity, so r would be lower (for a given h) Or friction would dissipate energy, so r would be lower (for a given h) * (The gradient and) the value obtained for e would be smaller [dependent on MP1]

Question 34

State why this does not show that the results are reproducible.

Answer 34

The second student carried out the same experiment

Question 35

The student shone the light from the bulb onto a light dependent resistor (LDR). The student measured the resistance of the LDR using an ohmmeter. The student plotted a graph of the resistance of the LDR against the power of the bulb. Describe how the student could have obtained the set of data required to plot the graph. Your description should include how to ensure that the data is accurate

Answer 35

Calculate power using P = VI  Repeat experiment and calculate mean  Vary p.d. to obtain at least five sets of data  Describes method to control background light Or describes controlling distance from LDR to light source

Question 36

) Describe how the student could check that the bracket was horizontal.

Answer 36

Measure the distance to the floor in two places using the metre rule Or place a spirit level along the bracket Or place a set square between the wall and the bracket Or place a protractor along the wall at the hinge Or correct description of applying Pythagoras theorem to the 3 measured lengths (

Question 37

how to find volume

Answer 37

* Use of a displacement can filled with water * Multiple coins added and volume of displaced water measured using a measuring cylinder * Volume of displaced water divided by number of coins * Coins added slowly to prevent splashing Or measuring cylinder read at eye level to avoid parallax Or ensure measuring cylinder is vertical Or displacement can is filled until overflowing and waits until drips stop

Question 38

The line of best fit on the graph does not pass through the origin. Describe a possible cause for this error, and how the student could reduce the effect of this erro

Answer 38

Normal line not correctly drawn at 90˚ to the flat surface * Use a protractor/set square to check the normal line * Zero error because protractor not aligned correctly * Ensure the protractor is aligned to the normal * Ray of light not directed to centre of the flat surface Or incident ray not perpendicular to curved surface * Mark the position of the centre of the flat surface on paper * Block moved * Mark the position of the block on paper Or tape the block in position * Did not repeat measurements with angles of incidence either side of the normal * Repeat measurements (for angles of incidence on both sides of the normal) and calculate mean value

Question 39

) Describe how the student could determine an accurate value for the thickness of the graphite pencil shading. The method should use a suitable graph.

Answer 39

Use ruler to measure length between the electrodes and measure width of shading Or measure length between electrodes and width of shading using the squared paper  Measure R at different values of length  Plot graph of R vs length  Calculate thickness using gradient = resistivity / (width thickness)

Question 40

Identify a possible source of systematic error in your method

Answer 40

ontact resistance between electrode and pencil shading  Zero error on ohmmeter (Accept zero error for a suitable measuring device named in (b)(i))  Electrodes not paralle

Question 41

Identify a health and safety issue for the student and how it may be dealt with.

Answer 41

Loud sound could damage hearing/ears (accept named part of the ear e.g., ear drum)  Wear ear defenders/plugs Or limit the volume of sound Or limit the duration/time of the exposure Or do not stand too close to the loudspeakers

Question 42

Describe two techniques the student should use to make this measurement as accurate as possible. hookes law

Answer 42

Attach a marker to the spring Or use a set square between ruler and spring Or ensure ruler is close to spring  View the scale at right angles  Ensure the ruler is at zero at the support  Ensure the ruler is vertical using a set square

Question 43

Describe how different apparatus could be used to measure the time, so that the percentage uncertainty is reduced.

Answer 43

Place a light gate (at each marker)  To (start and) stop an electronic/digital timer Or use a datalogger/computer to determine the time OR  Use video camera  Valid method to find time (e.g., count the number of frames)

Question 44

micrometer

Answer 44

HER * Check for zero error (on the micrometer) * to remove systematic error OR * Prevent over-tightening/deformation * By using the ratchet when closing

Question 45

Explain the purpose of the convex lens.

Answer 45

Using the lens produces a parallel beam of light Or using the lens concentrates the light on the solar cell * The light from the filament bulb spreads out Or to increase the intensity of light Or to ensure the intensity of light is even

Question 46

Describe two advantages of using solar cells to power a small water pump in a garden

Answer 46

Solar cells do not emit greenhouse gases [accept a named greenhouse gas] Or using solar cells does not contribute to global warming Or using solar cells would not cause acid rain Or using solar cells would reduce the need for fossil fuels * Solar cells use a renewable energy source * Sunlight/energy used is free * No need for mains wiring Or can be used where there is no mains electricity

Question 47

The student used vernier calipers to measure the diameters of the rings on the curved screen. (i) Give two reasons why vernier calipers are more appropriate for these measurements than a transparent ruler.

Answer 47

The vernier calipers have a smaller resolution Or the vernier calipers have a lower uncertainty * The vernier calipers can measure without parallax error * Tips of vernier calipers are easier to align with the rings (as surface is curved)

Question 48

The student’s investigation involves a small random error and a large systematic error. For each of these, suggest a source of the error and a realistic modification to the procedure which would reduce it.

Answer 48

Random error: EITHER * Difficult to judge exactly when current becomes 0 (so exact stopping p.d. is difficult to identify) * Use a more sensitive ammeter (e.g. picoammeter) OR * Background light could affect wavelength/colour * Block background light Or put the colour filter directly above the photocell Systematic error: EITHER * Colour filters do not give monochromatic light Or colour filters could give a range of wavelengths/colours/frequencies Or colour filters might be damaged and let through other wavelengths/colours/frequencies * Use a monochromatic light source Or use a light source with a narrower wavelength/frequency band Or use a light source with a single colour (e.g. LEDs / lasers) OR * Zero error of the ammeter/voltmeter * Check ammeter reading is zero while no light is shining Or check voltmeter reading is zero while apparatus is switched off Or check ammeter/voltmeter reading is zero

Question 49

The student used vernier calipers to measure the thickness y of the stack of paper. Explain how to make it more accurate

Answer 49

Check for zero error * (Correct the value) to eliminate systematic error MP2 dependent on MP1 OR * Repeat measurement in different places and calculate a mean * To reduce the effects of random error MP2 dependent on MP1 OR * Do not use excessive force when tightening the jaws * As this could introduce a random error

Question 50

Explain why making measurements on the whole stack of paper is better than making measurements on a single sheet of paper.

Answer 50

The measurements (of thickness and mass) are larger * So, the percentage uncertainty is smaller (for the same uncertainty) MP2 dependent on MP1 OR * For a single sheet, the measurements (of thickness and mass) are smaller Or for a single sheet, the measurement (of thickness and mass) is too small * So, the percentage uncertainty is larger (for the same uncertainty)

Question 51

) Describe how she should measure a single value of the height gained as accurately as possible.

Answer 51

Clamp/fix the metre rule in position * Ensure the metre rule is vertical using a set square * Place the metre rule close to the mass Or read the height from bottom of the mass Or attach a marker to the mass * Take measurements perpendicular to the scale, e.g. using set square

Question 52

) Explain why repeat measurements are appropriate for this measurement.

Answer 52

Random error will cause variation/anomalies in the values (accept suitable examples of random error e.g. reaction time, parallax error when measuring height) * (Repeat readings) allow a mean to be calculated to give a (more) accurate value

Answer 53

Laser light may cause damage/irritation to the eye Or laser light may temporarily dazzle the student * Do not look (directly) into the laser beam Or stand behind the laser Or wear dark lens safety glasses (accept light absorbing glasses) Or avoid reflective surface

Question 54

Explain how the student could modify the arrangement of the apparatus to reduce the percentage uncertainty in this value

Answer 54

* Increase the distance between the hair and the screen Or use a laser with a longer wavelength * As this will increase the separation between minima MP2 dependent on MP1 OR * Use a measuring device with a higher resolution (accept named device e.g., vernier caliper) * As this will reduce the uncertainty in the measurement

Question 55

Explain how two sources of error can be reduced in this investigation

Answer 55

Cannot measure to the centre of the filament bulb * So, measure the diameter of bulb separately and add the radius to the measurement of d * Parallax error when measuring d (using the metre rule) * Use a set square between the ruler and the sensor/bulb Or ensure eyes are perpendicular to the metre rule when taking measurements * Background light will affect the readings on the light meter * So, conduct the investigation in a dark room Or cover the apparatus to block background light Or measure and subtract the intensity of the background lig

Question 56

Identify two health and safety issues and how they should be dealt with.

Answer 56

The stand may topple over Clamp (the base of the stand) to the bench Or Place a heavy mass on the (base of the) stand Or Turn the base (of the stand) round (by 180) The (rubber) band may hit the student in the eye/face Or The (rubber) band may damage the eye Wear eye protection

Question 57

The student removed one rubber band from the freezer and determined the breaking force. He repeated this for the other rubber bands. Explain why it is appropriate to repeat the measurements.

Answer 57

(Repeating the measurement) reduces (the effect of) random error (Caused by) variations in the temperature of the rubber bands

Question 58

The student wrote a laboratory report about her investigation. She reported that the most significant source of error was being unable to judge the exact point where the ball landed. This was because the ball moved too quickly. Explain one modification she could make to the apparatus to reduce this error. You should include additional appara

Answer 58

Use a camera to record the motion Which can be viewed in slow motion (to find the exact point where the ball landed) OR Place a tray of sand on the bench for the ball to land in So that the ball remains stationary when it lands Or so the ball leaves an indentation where it lands

Question 59

Describe a method to determine a single value of s as accurately as possible, using a metre rule

Answer 59

lamp the metre rule in position Or Ensure the metre rule is vertical using a set square [allow spirit level] Or Place metre rule close to the tube Check the zero of the metre rule is level with the bottom of the transducer Or Check the zero of the metre rule is level with the surface of the water Or Measure to the surface of the water and to the bottom of the transducer and subtract the values Accept any valid method to determine s View (the metre rule) perpendicularly Or Use a set square to take the measurement from the metre rule

Question 60

Explain another technique she should use to determine an accurate value for d.

Answer 60

Check (and correct) for zero error To eliminate systematic error MP2 dependent on MP1 OR Use the ratchet (to prevent overtightening) To reduce (the effect of) random error

Question 61

Explain why the fixed resistor is included in the circuit.

Answer 61

The fixed resistor limits the (maximum) current in the circuit So the wire/circuit does not overheat Or so there is not a short circuit Or so the ammeter/battery is not damaged