Getting Good Results

Question 1

A good experiment is one which gives what kind of results?

Answer 1

Precise.
Repeatable/reproducible.
Valid.
Accurate.

Question 2

Precision.

Answer 2

Precise results don’t vary much from the mean.

Precision is reduced by random error.

Question 3

Repeatable/reproducible.

Answer 3

Repeatable results mean if the same person repeats the experiment using same method/equipment, they will get same results.
Reproducible means if a different person does experiment with slightly different methods/equipment the results will be the same.

Question 4

Validity.

Answer 4

Answer original question.

To do this you need to control all variables to make sure you’re testing one thing.

Question 5

Accuracy.

Answer 5

Accurate results are very close to true answer.

Human interpretation can reduce accuracy of results.

Question 6

What 4 things should you consider when designing a good experiment?

Answer 6

Variables.
Controls.
Repeats.
Sample sizes.

Question 7

What are variables?

Answer 7

Quantities that have potential to change.
eg temp or pH.
In an experiment you change one variable and measure its effect on another variable.

Question 8

What is the independent variable?

Answer 8

The variable that I change.

Question 9

What is the dependent variable?

Answer 9

The variable you measure.

Question 10

What is the control variable?

Answer 10

The variable you keep constant.

Question 11

Name the independent, dependent and controls in an investigation on light intensity affecting rate of photosynthesis?

Answer 11

Independent variable - light intensity.
Dependent variable - rate of photosynthesis.
Controls - pH, temperature, time.

Question 12

What are negative controls?

Answer 12

They are used to check that only the independent variable is affecting the dependent variable.
They don’t effect experiment.

Question 13

Example of a negative control.

Answer 13

When investigation how light intensity impacts rate of photosynthesis, set up a negative control in which the experiment is carried out in the dark.
No photosynthesis should happen.

Question 14

What is a positive control?

Answer 14

They show what a positive result of the experiment should look like, to check if its possible.

Question 15

Example of a positive control?

Answer 15

If you’re testing the presence of glucose in a solution.
Carry out Benedict’s test on a sample you know contains glucose.
This will show what a positive result should look like.

Question 16

What are control groups?

Answer 16

A group which is treated the same way as the experimental group, apart from factor you’re investigating.

Question 17

Why is doing repeats good?

Answer 17

Reduce random error.
Precise.
Repeatable.
Reduces the likelihood the results are due to chance.

Question 18

How can you reduce chance of random error?

Answer 18

Take several repeats.

Calculate mean.

Question 19

Why is sample size important?

Answer 19

Having a large sample size reduced the likelihood the results are due to chance.
If you get the same result over a large sample size it shows you have a representative sample.

Question 20

What should you do when doing a study involving humans?

Answer 20

Make sure the other variables are the same.

Same age, sex, ….

Question 21

Why is a placebo important?

Answer 21

So people don’t assume they have improved when they haven’t, because they think they have been treated.

Question 22

How do scientists find out if a result is due to chance or not?

Answer 22

Statistical test.