Paper 3 General

Question 1

What should you do when experimental data is to a set amount of sf?

Answer 1

Round all your answers calculated using that data to that amount of sf.

Question 2

What are the independent, control and dependent variables?

Answer 2

Independent - one you change.
Dependent - one measured and affected by the independent.
Control - may affect the outcome too, are measured and controlled so they are constant. Hopefully.

Question 3

What is the definition of error?

Answer 3

The difference between a measured result and the true value

Question 4

What are random errors?

Answer 4

Due to way instruments work - will give different values each time it is measured. Create uncertainty.

Question 5

How do you reduce the effect of random errors?

Answer 5

Use error bars, draw lines of best fit.

Question 6

What are systematic errors?

Answer 6

Create results consistently too large/small, due to errors such as poor technique (e.g parallax), zero error, poor calibration.

Question 7

What is zero error?

Answer 7

Error when the measuring instrument is not set to zero. Creates systematic error - zero value should be subtracted from each value.

Question 8

What is an accurate measurement?

Answer 8

Close to the true value.

Question 9

What is a precise set of measurements?

Answer 9

Set of measurements that are close together.

Question 10

What is the uncertainty of a reading, given the resolution of the instrument?

Answer 10

At least half the resolution. So +_ 1/2 of the res.

Question 11

What is the uncertainty of a MEASUREMENT, given the resolution of the instrument?

Answer 11

At least +_1 of the resolution. For example, a non-zero ended ruler. Or a stopwatch START AND STOP.

Question 12

How do you calculate percentage uncertainty?

Answer 12

Uncertainty / value x 100%

Question 13

How do you combine uncertainties?
(3 ways)

Answer 13

For adding or subtracting, add the absolute uncertainties.
For multiplication/division, add the percentage uncertainties.
For raising to a power, multiply the percentage uncertainty by that power.

Question 14

How do you read a vernier calliper?

Answer 14

Check where zero on small scale is on main scale, will be main reading. Then find lines that are EXACTLY lined up, will give you your decimal place.

Question 15

How do you read off a micrometer?

Answer 15

First close it until it just clicks. Use ratchet! Apart from that okay, find dist. along main scale then add the value shown on barrel.

Question 16

What is the % uncertainty for repeat measurements?

Answer 16

(1/2 x range / mean value) x 100%

Question 17

What are set-squares useful for?

Answer 17

Ensuring accuracy by eliminating parallax error and making sure objects are at right angles.

Question 18

How do you accurately count oscillations?

Answer 18

Say ‘zero’ when starting to time, use a fiducial marker to mark centre, only start timing after 1/2 oscillations, try and time at least 20 osc. if possible.

Question 19

When are data loggers useful?

Answer 19

For events that happen over a short space of time and produce a lot of data. Gives a very high sample rate.

Question 20

What are error bars based on?

Answer 20

Either half the range or the absolute uncertainty.

Question 21

How do you determine the uncertainty in a gradient?

Answer 21

Determine the steepest or shallowest gradient (error bars) then do:
((Highest or lowest grade - grad of best fit) / grad of best fit) x 100%