Paper 6 R#1

Question 1

General Experimental Basics

Question 2

What must you check before using a micrometer or balance?

Answer 2

Check zero reading.

Question 3

What should you do with a stopwatch before timing?

Answer 3

Reset to zero before using.

Question 4

How should you use a rule for measurements?

Answer 4

Start measuring from the 0 mark.

Question 5

How do you correct for one-tenth divisions on a scale?

Answer 5

Multiply your measurement by 10 to get the correct value (one tenth=1/10).

Question 6

What limits of experimental accuracy are assumed if an experiment is done with reasonable care?

Answer 6

± 10 %, calculated as (\frac{uncertainty}{measured\ value} \times 100).

Question 7

How many repeats should you do for reliable readings and how many data sets to provide?

Answer 7

Repeat experiments at least 5–6 times and provide 5 data sets in experiment questions.

Question 8

How do you obtain more reliable readings?

Answer 8

Repeat and average. In every seven or six marker, write “repeat and average.”

Question 9

Lenses & Mirrors

Question 10

When determining the focal length of a lens, what precautions ensure reliable readings?

Answer 10

• Darkened room
• Object and lens perpendicular to vertical
• Object and lens at same height from bench
• Move screen (not lens) slowly/backwards and forwards
• Clamp rule/fix rule to bench

Question 11

When using optical pins, what should you look at and why?

Answer 11

Look at the base of the pins because they may not be vertical elsewhere.

Question 12

What minimum separation and pin characteristic ensure accuracy in pin-based ray tracing?

Answer 12

Pins must be at least 5 cm apart and thin.

Question 13

What are possible causes of inaccuracy when measuring angles of reflection?

Answer 13

Thickness of lines, pins, or mirror.

Question 14

What are the key properties of images formed by lenses and mirrors?

Answer 14

Properties of image formed by lens; properties of image formed by mirror.

Question 15

Electricity

Question 16

What precautions should you take when using a voltmeter or ammeter?

Answer 16

• Take readings multiple times and average
• Check for zero error before starting
• Look perpendicular to scale to avoid parallax error

Question 17

What difficulties might arise in resistance wire experiments?

Answer 17

• Wire not uniform
• Contact between wire and crocodile clip imprecise
• Difficulty judging clip position

Question 18

Thermal Physics

Question 19

When investigating the rate of cooling of water, what variables must be kept constant?

Answer 19

• Initial temperature of water
• Same volume of water
• Room temperature (avoid draughts)
• Density/amount/type of insulation
• Thickness of lids/identical lids

Question 20

Why do we reduce rather than prevent energy heat loss in the cooling experiment?

Answer 20

NB: We reduce not prevent the energy heat loss.

Question 21

Moment Experiments

Question 22

Why might the pivot not be exactly at the 50.0 cm mark of the rule?

Answer 22

Center of mass of ruler not at center.

Question 23

What are sources of inaccuracy in moment experiments?

Answer 23

• Test load not exactly the stated weight (N)
• Meter rule not uniform

Question 24

Pendulum/Spring

Question 25

How do you measure curved-surface lengths accurately?

Answer 25

Use two blocks and a ruler.

Question 26

How is extension calculated?

Answer 26

Stretched length minus initial unstretched length.

Question 27

General Experimental Problems & Solutions

Question 28

How to solve inability to measure time of high-speed objects?

Answer 28

Use slow-motion video camera and play back.

Question 29

How to measure distance from centre of lens to screen?

Answer 29

Draw a vertical line on lens holder.

Question 30

How to measure time of one swing if too fast?

Answer 30

Time 10 swings then divide by 10.

Question 31

Moment-specific Solutions

Question 32

How to prevent mass from falling off in moment experiment?

Answer 32

Tape it.

Question 33

How to stop ruler sliding above pivot?

Answer 33

Fix it onto pivot.

Question 34

How to obtain balance if difficult?

Answer 34

Balance ruler over point where it just tips either way.

Question 35

Important Questions & Model Answers

Question 36

Why might different students obtain different resistance results despite careful work?

Answer 36

• Different heating effects; wires at different temperatures • Different interpolation between meter marks • Cell may run down/power less

Question 37

How to find best screen position reliably when exact focus is hard to decide?

Answer 37

Move screen slowly/carefully back and forth until best image found.

Question 38

Describe two techniques to obtain a clearly focused image.

Answer 38

1. Slowly move screen back and forth until clear image forms 2. Do experiment in darkened room

Question 39

Describe one technique to improve accuracy when measuring time for 10 oscillations.

Answer 39

Use fiducial point.

Question 40

How to write conclusion on effect of surface area on cooling rate?

Answer 40

State which beaker cooled faster in given time and refer to table values (don’t calculate rate).

Question 41

Safety Precautions

Question 42

What safety precautions for spring experiments?

Answer 42

1. Stay away from bench to avoid falling objects 2. Wear goggles to avoid spring snapping

Question 43

What safety precautions for electrical experiments?

Answer 43

1. Avoid wet hands 2. Avoid damaged insulation

Question 44

What safety precautions for heating experiments?

Answer 44

1. Stay away from hot objects 2. Wear gloves

Question 45

Electrical Symbols

Question 46

Image Properties

Question 47

What are the properties of images formed by plane mirrors?

Answer 47

From original sheet: refer to properties of image formed by mirror.

Question 48

Physics ATP Analysis: Additional Q&A

Question 49

Why take 5 readings and divide by 5 instead of one reading?

Answer 49

To reduce timing errors due to human reaction time and start/stop errors.

Question 50

How to obtain more reliable readings?

Answer 50

Repeat and average; for seven/six markers, note ‘‘repeat and take average’’ for at least six values; always include units in tables.

Question 51

How to justify relationship between two quantities?

Answer 51

State "within limits of experimental accuracy" and plot a graph whenever possible.

Question 52

How to accurately measure liquid volume in a measuring cylinder?

Answer 52

Read bottom of meniscus with line of sight perpendicular to scale.

Question 53

How to measure diameter of a rod?

Answer 53

Place rod between two blocks and measure gap at least twice and average; or use micrometre/vernier calipers, measure several points and average.

Question 54

What precautions when measuring volume of wooden rod?

Answer 54

Wood may absorb water; measuring cylinder scale not precise.

Question 55

How to calculate gradient of a graph?

Answer 55

Draw the largest triangle on graph and use its values to calculate gradient.

Question 56

Why take a trial reading?

Answer 56

To check if dependent variable measurable, if independent variable range appropriate, and to establish suitable d and t values.

Question 57

How to ensure a scale is horizontal?

Answer 57

Measure distance from bench at two ends of rule and adjust until equal.

Question 58

How to position load accurately from pivot on metre rule?

Answer 58

Mark centre line of mass; suspend load from loop of thread and align with rule mark; measure block width and add half-width to 5.0 cm for block edge position; take mean of edge marks.

Question 59

How to make pendulum length l accurate?

Answer 59

Measure top of bob, add half-diameter measured with blocks and ruler/callipers; measure top and bottom and average; view perpendicular; keep rule parallel to string, use set-square; rule close to pendulum; measure from bottom of clamp.

Question 60

Why might pivot not be at 50.0 cm mark?

Answer 60

Centre of mass of ruler not at center.

Question 61

What are sources of inaccuracy in pendulum/spring extension experiment?

Answer 61

Test load not exactly 1.0 N; spring extension not linear; metre rule not uniform.

Question 62

How to get accurate thermometer readings?

Answer 62

Read with line of sight perpendicular; wait until reading stabilises; stir before reading; avoid contact with container sides/bottom; if comparing two beakers, keep thermometer at same depth.

Question 63

What control variables when measuring heating/cooling rate?

Answer 63

Same volume, initial temperature, surface area, diameter, height, room temperature, beaker material, experiment duration.

Question 64

How to reduce thermal energy loss from beaker?

Answer 64

Use insulation, lid; adjust starting temperature or room temperature; change water volume or surface area.

Question 65

How to test lid effects on cooling rate?

Answer 65

Repeat experiment without lid; calculate cooling rates and subtract.

Question 66

What errors in ray trace experiments?

Answer 66

Finite ray thickness; difficulty aligning pins; pins too thick; inaccuracies greater for small angles.

Question 67

What precautions in ray tracing?

Answer 67

Use thin lines/pins; view pin bases; ensure pins far apart and vertical.

Question 68

Why is 2.7 cm pin separation unsuitable?

Answer 68

Separation too small; larger separation gives greater accuracy.

Question 69

What difficulties in resistance wire experiments?

Answer 69

Judging crocodile clip position; measuring wire to nearest mm; clip contact not precise; interpolating meter readings.

Question 70

If replacing resistance wire with variable resistor, how to connect?

Answer 70

Place variable resistor in series.

Question 71

Disadvantages of not using a variable resistor?

Answer 71

Cannot obtain continuous values; less straightforward to change current; harder to get many values.

Question 72

Precautions in lens experiments?

Answer 72

Darkened room; bright lamp; move screen slowly; mark centre of lens; clamp rule; keep lens, object, screen vertical; repeat and average.