Mod 3 Prac Task

Question 1

How is experimental quality assessed

Answer 1

Accuracy: feature of results
Reliability: feature of results
Validity: feature of the method

Question 2

Define accuracy
How is it improved

Answer 2

The extent to which a measured value agrees with its true value
It is improved by:
minimising avoidable systematic errors
Taking an average of multiple trials (discarding outliers) to minimise random error
Using better equipment (instrument accuracy) due to more sensitive or smaller increment scale

Question 3

Define reliability
How is it improved

Answer 3

The extent to which the findings of repeated experiments, conducted under identical or similar conditions, are consistent with each other.
Cannot be improved rather it is evaluated through the repetition of experiments and comparing corresponding results
Reducing the no of experimenters may increase the reliability of results
If the results are obtained properly and are repeatable, then the experiment can be evaluated as reliable

Question 4

Define validity
How it is improved

Answer 4

Validity refers to whether all the variables within an experiment, apart from the independent and dependent, were controlled.
Is a property of the method itself
If the method is compromised by poor apparatus choices, incorrect chemistry techniques or incorrect assumptions, then the experiment is invalid
To ensure validity:
Implement a control
Controlling all variables that may impact the dependent variable. Must ensure only 1 independent variable exists
Using objective (quantitative) measures where possible

Question 5

True or False
If sensitive apparatus is used, the results will be accurate

Answer 5

False
the method could be invalid

Question 6

True or False
Joel wishes to test whether sunlight is required for plants to grow. Temperature and water are examples of some controls he can apply

Answer 6

False
if temperature and water are used as controls, independent variable still exists therefore making it an invalid experiment with two independent variables. Control must have no independent variable

Question 7

True or False
If an experiment is invalid, then the results are almost certainly inaccurate

Answer 7

True
As an invalid experiment cannot produce accurate results in most scenarios

Question 8

What does the conclusion include

Answer 8

Address the Aim – i.e. did you achieve your aim? did you find out the thing you wanted to, and if so, what was the answer?
Address the Hypothesis – i.e. Was your hypothesis ‘supported’, or ‘refuted’ (found to be incorrect)

Question 9

Features of graph

Answer 9

All graphs must have certain features:
Heading – a name for the graph, which shows what it is all about.
Horizontal axis, also called the X axis– the line across the bottom of the graph. MUST be used for your INDEPENDENT VARIABLE
Vertical axis, or Y Axis – the line up the left side of the graph. This is where you put your dependent variable.
Axis titles – both axes need titles, so we know what they are showing.
Units – both axes should also include the units for whatever you are measuring, usually in brackets after the axis title (cm, kg, N, etc).
Scales – both the X and Y axis need scales. These are the marks and numbers that allow us to put the points in the right places. They must be evenly spaced

Question 10

Type of graphs used to depict results

Answer 10

A column graph is used when your data is qualitative (i.e. not in numbers), e.g. fruit, colours, brands, etc.
A line graph is used when your data is quantitative (i.e. measured using numbers), e.g. time, temperature, volume, weight, etc.
Line graph is preferred

Question 11

What characteristics are required for the results section

Answer 11

Include:
Title (heading for the table overall)
Headings for columns and rows
Correct number of rows and columns
Units (should be in the headings of the columns, not after each measurement
Averages of results

Question 12

Checklist for hypothesis (What must the hypothesis have)

Answer 12

Is the hypothesis based on information contained in the research? Y/N
Does the hypothesis include the independent and dependent variables? Y/N
Have you worded the hypothesis so that it can be tested in the experiment? Y/N
Have you established design criteria?

Question 13

Golden rule to write a good method

Answer 13

The golden rule to writing a good Method section is to ask yourself whether your reader could replicate your study based on just the information you provided.

Question 14

Types of repetition in method

Answer 14

Repetition by doing the experiment again ‘from the start’. Eg after bouncing our ball on a surface, we bounce it again, and again, and again.
Replication where you have multiple copies of the ‘same’ experiment running at the same time. Eg. Testing fertiliser on plants, you will need 3 plants for fertilizer A, 3 plants for fertilizer B, etc. THIS is better if you can!

Question 15

Parts of risk assessment

Answer 15

There’s three parts to a Risk Assessment:
The RISK (aka Hazard) – i.e., what is dangerous in the experiment. There will probably be several risky objects or situations or things that can go wrong.
The INJURY – what injury could this risk cause you. Each risk may have multiple injuries.
The MANAGEMENT – how do we prevent this injury AND/OR what do we do if something goes wrong. There’s many different ways, like use something different, or wear protective clothing, or just be careful.
PRECAUTION

Question 16

Difference between constructive and destructive interference
Where does it occur?

Answer 16

Constructive interference: Two waves overlap in such a way that they produce a higher resultant amplitude
Occurs at antinodes
Destructive interference: Two waves overlap in such a way that they superimpose or produce a lower resultant amplitude
Occurs at nodes

Question 17

Define standing waves

Answer 17

Two waves with the same amplitude, wavelength and frequency travelling in opposite directions will interfere and produce a combined wave.
Frequencies that produce standing waves are called resonant frequencies.

Question 18

Define progressive wave (travelling wave)

Answer 18

A wave which travels continuously in a medium in the same direction without a change in its amplitude

Question 19

When does resonance occur?
What effect does it cause

Answer 19

Occurs when object is exposed to driving frequency equal to object’s natural frequency. Has the effect of increasing the amplitude of object’s vibration due to constructive interference.

Question 20

Difference between driving and natural frequency

Answer 20

The frequency of an oscillating force applied to the system from an external source.
The natural frequency is the frequency at which a system would oscillate if there were no driving and no damping force.

Question 21

Define superposition

Answer 21

Superposition: when waves in a medium interfere with each other, amplitude of the individual wave pulses add together to give amplitude of total disturbance of medium

Question 22

Law of reflection

Answer 22

Angle of incidence is equal to the angle of reflection
Note: angle of refraction isn’t equal to angle of incidence

Question 23

relationship between focal length and radius of concave or convex mirror

Answer 23

focal length is equal to half of the radius of curvature

Question 24

What happens to light rays once they pass through concave or convex lenses or mirrors

Answer 24

Convex lens converges the light rays and concave lens diverges the light rays. Applies for biconvex and biconcave lenses as well.

Question 25

Define angle of incidence and reflection and normal

Answer 25

Angle between incident ray and normal Angle between reflected ray and normal An imaginary line perpendicular to the reflective surface

Question 26

What is the C in concave and convex lens diagram

Answer 26

Centre of curvature which is on principle axis

Question 27

Relationship between pitch and frequency and loudness and amplitude

Answer 27

High-frequency sound waves are perceived as high-pitched sounds, while low-frequency sound waves are perceived as low-pitched sounds. The louder the sound, the higher the amplitude of the wave, and the softer the sound, the smaller the amplitude of the wave.

Question 28

Relationship between light intensity and distance

Answer 28

There is an inverse relationship between distance and light intensity – as the distance increases, light intensity decreases.

Question 29

When does total internal reflection occur

Answer 29

When the angle of incidence is larger than the critical angle

Question 30

How to find angle of incidence and reflection in practical

Answer 30

Place a ray box and plane mirror onto a sheet of paper Mark in the position of the mirror with a pencil. Project a ray of light from a single slit into the mirror. Draw in pencil the path of the rays. Do this by drawing dots on the rays and connecting them with a ruler. Measure different angles of incidence using a protractor. Include an angle of incidence of zero degrees into your measurements

Question 31

How to find the focal point of a concave mirror experimentally

Answer 31

Set up the ray box with triple slit so that three rays of parallel light hit a concave mirror at the centre. You should see three light rays reflecting back into each other at a point called the focal point

Question 32

How to find the virtual focus of convex mirrors

Answer 32

Set up the ray box with triple slit so that three rays of parallel light hit a convex mirror at the centre. You should see three light rays diverging away from the mirror, trace the rays backwards until you find their supposed source which is the virtual principal focus

Question 33

How to find the critical angle with a semicircular perspex block

Answer 33

Set up the semicircular perspex block and shine a ray of light so it hits the centre of the block. As the light hits the block at a 90 degree angle to the surface, no bending occurs. Increase the angle of incidence until at one angle, no light is refracted but totally internally reflected

Question 34

How to totally internally reflect light rays in a perspex prism

Answer 34

Connect the ray box to the power supply. Place the ray box over a page of your notebook. Use one of the black plastic slides in the ray box kit to produce a single thin beam of light which is clearly visible on the white paper. Place a Perspex triangular prism on your notebook and direct the thin beam of light towards it. Observe the beam as it passes through the prism. Turn the prism slightly anticlockwise, closely observing the thin light beam as it travels from the Perspex prism back into the air. Continue to turn the prism until the beam no longer emerges from the prism.

Question 35

How to measure light intensity

Answer 35

Use a 12V light globe as light source. Mount this onto a trolley and then move it away from the sensor in graduated steps. Use a metre ruler to accurately measure distance. End results should show distance vs light intensity. Shouldn't show direct proportion so find out what value must be added to all the values received to produce a graph of direct proportion.

Question 36

How to know if lens is converging or diverging

Answer 36

Use the triple slit of the light ray box and project three light rays at the middle of the lens. If it is biconcave it will diverge away and if biconvex, it will converge

Question 37

how to observe the refraction of light and to use Snell’s Law to determine the refractive index of a medium

Answer 37

1. Place the block in the middle of the A4 page. Use a pencil to draw around the block so that it can always be returned to the same position. Mark a point on the boundary and label it as O. 2. Reduce the amount of light in the room (by drawing curtains etc.). Turn on the ray box and direct a single ray of light so that it enters the block at point O at an angle and emerges on the other side of the block. 3. Without moving the ray or the block, mark 3 points along each of the incident ray and the emerging ray. Place a mark at the block boundary at the point where the light ray emerges from the block and label this R. 4. Turn off the ray box and remove the block from the paper. Using your pencil marks as guides, use a ruler to draw the path of the incident ray into the block, joining points O and R, and to draw the path of the emerging ray. Draw normals to the surface at points O and R. 5. Use your protractor to measure the angle of incidence θ1 and the angle of refraction θ2 as shown in the figure below. Enter these values into table 10.4A. 6. Repeat steps 1–6 for three other incident angles.

Question 38

State metric prefixes

Answer 38

Thieves Graded Minesweepers Kindly However DAshing Dilbert Captured Musty Mickey Nelly Poignantly tera: 10^12 giga: 10^9 mega: 10^6 kilo: 10^3 hecto: 10^2 deka: 10^1 deci: 10^-1 centi: 10^-2 mili: 10^-3 micro: 10^-6 nano: 10^-9 pico: : 10^-12

Question 39

Formula for wave number

Answer 39

The number of waves per unit distance 𝑘=2𝜋/𝜆 waves per metre (m-1)

Question 40

Define period

Answer 40

The time taken for one complete oscillation in the density of the medium is called the time period of the wave.

Question 41

Position of Antinode vs node

Answer 41

2 nodes in first harmonic and 1 antinode Antinode between nodes

Question 42

Define natural vibration

Answer 42

Natural vibration: rate at which object oscillates at the same rate regardless of how hard it is hit, due to vibrational rate being determined by metal it is made from, its length and spacing of its prongs.

Question 43

Similarities and differences between em and mechanical waves

Answer 43

Similarities: transfer energy, don't transfer mass, both are produced by original disturbance Differences: Mechanical waves are longitudinal or transverse, require a medium, travel far slower than em waves Em waves only transverse, no medium required, travels far quicker than mechanical waves

Question 44

Describe sound intensity

Answer 44

Intensity of sound wave is a measure of the amount of energy able to transfer to a square metre of surface in a 1 second interval. I=P/A I=P/4πr² measured in W m^-2 I: intensity (watts per square metre/ Wm^-2) P: power (Js–1/W)

Question 45

Describe acoustic power

Answer 45

Acoustic power of source: The amount of sound energy produced by a source every second. Measured in joules P=E/t E: energy in joules t: time P: power (Js–1/W)

Question 46

Inverse square law for sound and light intensity

Answer 46

When comparing the sound intensities at two distances r1 and r2 from a source, it should be remembered that the power of the source is a constant. This relationship then gives the following useful formula: 𝐼2/𝐼1 =(𝑟1^2)/(𝑟2^2 ) 𝐼1r1^2=𝐼2r2^2 𝐼1: intensity 1 𝐼2: intensity 2 r1^2: radius 1 squared r2^2: radius 2 squared

Question 47

When are beat frequencies created

Answer 47

Beat can be created when two waves with the same amplitude with slightly different frequencies are superimposed (two transverse waves come together, and their frequencies cancel) to produce pulses or beats. =difference in frequencies =|𝑓1−𝑓2 | f1: first frequency (Hz) f2: second frequency (Hz) T=1/fb T: period fb: beat frequency

Question 48

Define doppler effect

Answer 48

This effect occurs when a course of sound waves is moving with respect to an observer. When approaching an observer, the sound waves have an apparent upwards shift in frequency. They have an apparent downwards shift in frequency when moving away from an observer f’=f (vwave + vobserver)/(vwave-vsource) f’: apparent or observed frequency f: original frequency vwave: speed of waves in the medium (ms^-1) Vobserver: speed of observer relative to the medium (ms^-1) Vsource: speed of source relative to the medium (ms^-1) NOTE: If the sound source is coming towards the observer, then 𝒗_𝒔𝒐𝒖𝒓𝒄𝒆 will be positive. If the sound source has passed the observer, then 𝒗_𝒔𝒐𝒖𝒓𝒄𝒆 is a negative value.

Question 49

Define standing wave

Answer 49

Two waves with the same amplitude, wavelength and frequency travelling in opposite directions will interfere and produce a combined wave. Frequencies that produce standing waves are called resonant frequencies.

Question 50

Formulas for strings with fixed ends

Answer 50

λ=2l/n First harmonic (fundamental frequency) f=v/λ=v/2l Second harmonic: f=v/λ=v/l Third harmonic: f=v/λ=3v/2l Fourth harmonic: f=v/λ=2v/l f=nv/2l λ: wavelength (m) l: length (m) n: ( no of harmonics) v: velocity (ms^-1)

Question 51

Formulas for strings with one fixed and open end

Answer 51

λ=4l/n f=nv/4l λ: wavelength (m) l: length (m) n: no of harmonic v: velocity (ms^-1) Only odd-numbered harmonics are possible as they can only satisfy the conditions of having a node at the fixed and antinode at the open end.

Question 52

Formulas for pipes with open ends

Answer 52

f=nv/2l λ=2l/n f: frequency (Hz) n: no of harmonics v: velocity (ms^-1) l: length (m) λ: wavelength (m)

Question 53

Refractive Index formula

Answer 53

n𝑥=c/v𝑥 n𝑥: refractive index of medium 𝑥 (no units) c: speed of light in vacuum v𝑥: speed of light in medium n1v1=n2v2 n1: refractive index of first material n2: refractive index of second material v1: speed of light in first material v2: speed of light in second material

Question 54

Snell's law

Answer 54

Snell's Law allows us to have a sense of what will happen to light at a interface given the indices of refraction and two media. 𝑛1 sin⁡𝑖=𝑛2 sin⁡𝑟 OR 𝑛1/𝑛2 =sin⁡ 𝜃2/sin⁡𝜃1 n1: refractive medium of incident medium n2: refractive medium of refracting medium i: angle of incidence ( can be written as 𝜃1) r: angle of refraction (can be written as 𝜃2)

Question 55

Define dispersion

Answer 55

Dispersion is defined as the spreading of white light into its full spectrum of wavelengths. When we view all of the colours of visible light mixed together, our eyes and brain interpret the result as ‘white light’. Can see different colours because waves of different wavelengths are slowed down or speed up by different amounts as they travel into a medium.

Question 56

Define critical angle

Answer 56

The critical angle (θc) is the incident angle that causes an angle of refraction of 90° (ie, the refracted ray travels along the edge of the boundary).

Question 57

Critical angle formula

Answer 57

Critical angle can be calculated using: sin⁡𝑖𝑐 =1/𝑛𝑥 𝑖𝑐= 𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 𝑎𝑛𝑔𝑙𝑒 𝑛𝑥=refractive 𝑖𝑛𝑑𝑒𝑥 𝑜𝑓 𝑚𝑒𝑑𝑖𝑢𝑚

Question 58

Difference between lens and mirror

Answer 58

The mirror is a device based on the principle of reflection whereas the lens is based on the principle of refraction.

Question 59

Specific heat capacity formula

Answer 59

𝑸 = 𝒎𝒄∆𝑻 Q: quantity of energy m: mass of substance (kg) c: specific heat capacity of substance (J Kg^-1K^-1 T: change in temperature (K)

Question 60

State the first law of thermodynamics

Answer 60

Change in internal energy of air=Heat energy applied to air - work done by air ΔU=Q - W U: internal energy (J) Q: heat energy applied W: Work done

Question 61

Latent heat formula Latent heat of fusion formula Latent heat of vaporisation formula

Answer 61

Q=mL Q: heat energy transferred in joules (J) m: mass in kg L: latent heat (J kg^-1)' Latent heat of fusion formula Q=mLfusion Q: heat energy transferred in joules (J) m: mass in kg Lfusion: latent heat of fusion (J kg^-1) Latent heat vaporisation Q=mLvapour Q: heat energy transferred in joules (J) m: mass in kg Lvapour: latent heat of vaporisation (J kg^-1)

Question 62

Thermal conductivity formula

Answer 62

𝑄/𝑡=(𝑘𝐴∆𝑇)/𝑑 Q/t: rate of heat energy transferred (J s^-1) k: thermal conductivity of the material (W m^-1 K^-1) A: surface area perpendicular to direction of heat flow (m^2) ∆𝑇: temperature difference across material in kelvin or degrees celsius d: thickness of the material through which the heat is being transferred (in m)

Question 63

What are the types of errors? What type of experiment minimises this?

Answer 63

Blunders: errors caused by carelessness Systematic: identifiable errors that can be fixed includes: environmental: when the surroundings cause problems with the lab observational: when the observer doesn't read the measurement correctly instrumental: the instrument is flawed and causes consistent inaccuracies in readings theoretical: when the experimental procedure is flawed, thus creating inaccuracies in the experiment An accurate experiment will have minimal or no systematic error Random: uncontrollable errors caused by fluctuations in variables including: environmental: the environment unpredictably changes affecting the experimental results observational: the observer's judgement leads to random inaccuracies A reliable experiment will minimise random error

Question 64

Do the pulses you produce in slinkies really carry energy

Answer 64

A pulse or a wave is introduced into a slinky when a person holds the first coil and gives it a back-and-forth motion. This creates a disturbance within the medium; this disturbance subsequently travels from coil to coil, transporting energy as it moves.

Question 65

Do the pulses lose energy in slinkies as they travel along?

Answer 65

It loses energy as it travels. Notice that if you move your hand upward and downward slowly, a longer pulse travels down the slinky. Notice that the longer pulse travels at the same speed as the shorter pulse.

Question 66

Relationship between pulse speed and tension of slinky

Answer 66

Stretch the spring tighter to increase its tension and therefore its pulse speed.

Question 67

Does the speed of a pulse depend on the amplitude of the pulse? Does the speed of a pulse depend on the length of a pulse?

Answer 67

The pulse speed depends on the properties of the medium and not on the amplitude or pulse length of the pulse.

Question 68

Do identical pulses travel at the same speed along identical slinkies

Answer 68

Since the speed of a wave (or pulse) is dependent upon the medium through which it travels, two pulses in the same medium will have the same speed.

Question 69

Formula for frequency

Answer 69

v/λ=f f=n/t=1/T f=frequencies n=number of cycles t: particular amount of time v=velocity λ=wavelength T: period

Question 70

Why does light reflect from the back surface of the mirror

Answer 70

Because this surface also reflects light as it is silvered meaning that more light will reflect of it than the front surface mirror made from glass due to its high reflectivity property across the visible spectrum, reflecting of light

Question 71

Why does the light not bend at 90 degrees to the surface for semicircular perspex blocks

Answer 71

No change in direction occurs because the ray of light enters the block at normal incidence

Question 72

When does light bend towards or away from the normal

Answer 72

Light passing from a less dense to a more dense medium bends toward the normal. Light passing from a more dense to a less dense medium bends away from the normal.

Question 73

relationship between the refractive index of the block, the angle of incidence and the angle of refraction

Answer 73

Refractive index =sine of the angle of refraction sine of the angle of incidence.

Question 74

Importance of data logger when measuring temperature

Answer 74

Are far more accurate than a thermometer as measurements are allowed to be taken automatically and precisely instead of thermometers which are subjected to parallax error

Question 75

How to find common temperature? Example: A chef pours 200g of cold water with a temperature of 15 degrees celsius into a hot aluminium saucepan with a mass of 250g and a temperature of 120 degrees celsius. What will be the common temperature of the water and saucepan when thermal equilibrium is reached. Assume no energy is transferred to or from the surroundings

Answer 75

Qw=Qs MwCwΔTw=MsCsΔTs ΔTw=Tf-15 ΔTs=120-Tf 0.200g x 4200J kg^-1°C^-1 x (Tf-15°C)=0.250g x 900J kg^-1°C^-1 x (120-Tf) 840Tf-12600=27000-225Tf 1065Tf=39 600 Tf=37°C Saucepan and water will reach a common temperature of 37°C

Question 76

State the sound intensity level equation

Answer 76

𝐿 = 10 log⁡(𝐼/𝐼_0 ) L: loudness (dB) softest sound audible (Io) , which is 10^-12 W m^-2 I: Intensity (Wm^-2)

Question 77

How to ray trace if object is between focal point and the mirror for a concave mirror

Answer 77

First draw a ray from the object to the mirror and then the ray going to bounce back to the focal point and then extend the line Then draw a ray that connects the object to the centre of curvature and then extend the line past the mirror

Question 78

How to ray trace if object is on other side of the mirror for convex mirrors

Answer 78

Draw a ray from the object to the mirror and then draw a dotted line towards the focal point and then extend the line with a real line. Then draw the second ray towards the centre of curvature and then extend the line

Question 79

Front of a concave and convex mirror is where

Answer 79

The front is on the left side whilst the behind is on the right side for both Note: Focal length of concave mirror is positive whilst convex mirror is negative

Question 80

What happens if an object is on the focal point

Answer 80

No image is formed as the radius is infinite

Question 81

What do images look like on a concave mirror with an object: Further than the centre of curvature Object located on the centre of curvature Located between centre of curvature and focus Located between mirror and focus

Answer 81

Real, inverted diminished images Real, inverted true images Real, inverted magnified images Virtual, upright magnified images

Question 82

What do images look like on a biconvex lens with an object: At infinity Between infinity and 2F At 2F Between 2F and F At F Between F and lens

Answer 82

No image Real, inverted diminished image between F and 2F Real, inverted true image at 2F Real, inverted magnified image between 2F and infinity No image Virtual image between 2F and F on left side

Question 83

Common uses for convex and concave mirrors

Answer 83

in magnification glasses, sunglasses, and rear view mirror in vehicles, ATMs, and street lights. Shaving mirrors. Head mirrors.

Question 84

Define diffraction

Answer 84

Diffraction is the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture.