Mod 3 Prac Task Flashcards
How is experimental quality assessed
Accuracy: feature of results
Reliability: feature of results
Validity: feature of the method
Define accuracy
How is it improved
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
Define reliability
How is it improved
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
Define validity
How it is improved
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
True or False
If sensitive apparatus is used, the results will be accurate
False
the method could be invalid
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
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
True or False
If an experiment is invalid, then the results are almost certainly inaccurate
True
As an invalid experiment cannot produce accurate results in most scenarios
What does the conclusion include
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)
Features of graph
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
Type of graphs used to depict results
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
What characteristics are required for the results section
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
Checklist for hypothesis (What must the hypothesis have)
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?
Golden rule to write a good method
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.
Types of repetition in method
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!
Parts of risk assessment
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
Difference between constructive and destructive interference
Where does it occur?
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
Define standing waves
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.
Define progressive wave (travelling wave)
A wave which travels continuously in a medium in the same direction without a change in its amplitude
When does resonance occur?
What effect does it cause
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.
Difference between driving and natural frequency
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.
Define superposition
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
Law of reflection
Angle of incidence is equal to the angle of reflection
Note: angle of refraction isn’t equal to angle of incidence
relationship between focal length and radius of concave or convex mirror
focal length is equal to half of the radius of curvature
What happens to light rays once they pass through concave or convex lenses or mirrors
Convex lens converges the light rays and concave lens diverges the light rays. Applies for biconvex and biconcave lenses as well.
Define angle of incidence and reflection and normal
Angle between incident ray and normal
Angle between reflected ray and normal
An imaginary line perpendicular to the reflective surface
What is the C in concave and convex lens diagram
Centre of curvature which is on principle axis
Relationship between pitch and frequency and loudness and amplitude
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.
Relationship between light intensity and distance
There is an inverse relationship between distance and light intensity – as the distance increases, light intensity decreases.
When does total internal reflection occur
When the angle of incidence is larger than the critical angle
How to find angle of incidence and reflection in practical
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
How to find the focal point of a concave mirror experimentally
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
How to find the virtual focus of convex mirrors
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
How to find the critical angle with a semicircular perspex block
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
