Variables
Define an independent variable
The variable that is changed by the scientist.
What does reliability mean in a scientific investigation?
Reliability means results are consistent when the experiment is repeated.
What is a hypothesis?
A testable prediction about what will happen in an experiment.
What type of graph is best used to display continuous data?
A line graph.
What type of wave is a sound wave?
Longitudinal wave
A student investigates how the concentration of salt affects the boiling point of water. Identify the dependent variable
The boiling point of the water
What does validity mean in a scientific investigation?
Validity means the investigation is fair and measures what it is supposed to measure.
Which variable is usually included first in a hypothesis?
The independent variable.
Why do scientists calculate an average in experiments?
To make results more reliable
What happens to the pitch of a sound when frequency increases?
The pitch becomes higher
In an investigation testing how light intensity affects photosynthesis in aquatic plants, give two controlled variables that must remain constant.
Examples: water temperature, type of plant, amount of water, carbon dioxide levels, lamp type.
Name one way a scientist can improve the reliability of an experiment
Repeat trials, increase sample size, or average results.
Complete this hypothesis: “If the amount of sunlight increases, then…”
“…the plant growth will increase.”
A result is very different from the other results collected. What is this called?
an outlier
Which part of a longitudinal wave has particles close together?
Compression
A scientist investigates how the pH of a solution affects enzyme activity. State the independent variable, dependent variable, and one controlled variable.
Independent = pH of solution
Dependent = enzyme activity/reaction rate
Controlled = temperature, enzyme concentration, volume, etc.
A student changes two variables at once during an experiment. Does this mainly affect reliability or validity, and why?
Validity, because it is no longer a fair test and it is unclear which variable caused the results.
Explain why a hypothesis must be testable.
So it can be investigated through observations, measurements, or experiments using evidence.
In a scientific graph, which variable goes on the x-axis and which goes on the y-axis?
The independent variable goes on the x-axis and the dependent variable goes on the y-axis.
Describe how sound travels from a source to your ear.
Pinna → ear canal → eardrum → ossicles → cochlea → auditory nerve → brain.
Explain why failing to control variables can reduce the validity experimental results.
Uncontrolled variables may affect the results, making it unclear whether the independent variable caused the change.
Scientists tested a new fertiliser on plants but used different amounts of water for each plant. Explain how this impacts the validity of the investigation.
The investigation is not valid because more than one variable was changed. Different amounts of water could affect plant growth, so it is unclear whether the fertiliser caused the results.
Identify the problem with this hypothesis: “Plants are cool and sunlight is important.”
It is not testable, measurable, or written as a prediction linking variables.
A student records these results: 3, 5, 5, 9, 13. What are the mode and the average (mean) of the data?
Mode = 5; Average (mean) = 7
Explain why sound cannot travel through space.
Sound requires particles to transfer vibrations, and space is a vacuum with no particles.