Practical Skills

Question 1

Which apparatus is used in the course?

Answer 1

Distance-measuring equipment:

• Metre rules
• Digital callipers
• Micrometers
• Travelling microscopes

Electrical meters:

• Ammeter
• Voltmeter
• Ohmmeters

Digital balances

Timers:

• Digital stopwatches
• Light-gate activated timers

Thermometers and temperature probes

Liquid volume measures:
-Measuring cylinders

Question 2

How can zero errors be dealt with?

Answer 2

It is important to ensure that all apparatus read 0 before an experiment. If the equipment cannot be zeroed, the result must deduct the original reading.

Question 3

What is the resolution of equipment? Why is it useful to know this?

Answer 3

In digital equipment, the resolution is 1 in the least significant figure in the display.

In analogue equipment, the resolution is the interval between the smallest graduations.

It is useful to know this figure to calculate uncertainties.

Question 4

How should data from an experiment be displayed?

Answer 4

Systematic data is usually presented by constructing a table. The table should contain headings, the independent variable readings in systematic order, readings to the resolution of the equipment, an average of repeat measurements, calculated data to a reasonable amount of significant figures.

Question 5

What is an outlier?

Answer 5

An outlier is a result which is very different from the others and is ignored when calculating averages.

Question 6

What is the difference between absolute uncertainties and percentage (relative/fractional) uncertainties?

Answer 6

An Absolute Uncertainty is denoted by the symbol “Δ“ and has the same units as the quantity calculated.

A Relative or Percentage Uncertainty is denoted by the symbol “ε“ and has no units (it is a % of the result).

Question 7

How do you find uncertainties in calculations for the calculated quantity?

Answer 7

Multiplying or dividing -
ADD the relative uncertainties.

Addition or subtraction -
ADD the absolute uncertainties.

For a number raised to a power -
MULTIPLY the relative uncertainty by the power.

Question 8

How can you calculate a relative uncertainty from an absolute uncertainty? How can you calculate an absolute uncertainty from a relative uncertainty?

Answer 8

Relative -> Absolute
Relative uncertainty/(100%) * Result = Absolute uncertainty

Absolute -> Relative
Absolute uncertainty/Result * (100%) = Relative uncertainty

Question 9

What is the arithmetic mean of a set of results?

Answer 9

The arithmetic mean is the sum of the values divided by the number of values.

Question 10

How can uncertainties be represented on a graph?

Answer 10

Uncertainties are presented in the form of error bars, the arithmetic mean of the repeat measurements for each result will be the centre of each error bar. The error bars are parallel to the axis on which the uncertainty is found.

Question 11

How can you find the best-fit straight line on a graph with error bars?

Answer 11

To find the line of best-fit, the steepest and shallowest lines are drawn so that they go through the error bars. The average gradient of these two lines is the gradient of the best-fit straight line.

Question 12

How can linear graphs test a linear relationship?

Answer 12

The equation y = mx + c is important to see relationships.
m- gradient
c- y-intercept

For example to see the linear relationship between V and I the equation V = -rI + E can be used. If V is plotted on the y-axis and I on the x-axis the gradient will be -r and the y-intercept will be the value of E.

Question 13

How can linear graphs test a non-linear relationship?

Answer 13

The equation y = mx + c is important to see relationships.
m- gradient
c- y-intercept

For example to see the non-linear relationship between v^(2) and x the equation v^(2) = u^(2) + 2ax can be used. If v^(2) in plotted on the y-axis and x on the x-axis then gradient of the line will be 2a and the y-intercept will be equal to u^(2).

Question 14

What are the two main purposes of practical work?

Answer 14

1. To test relationships between variables.

2. To determine the value of a physical quantity.

Question 15

What is a variable in an experiment? What are the different types of variables?

Answer 15

All quantities that need to be measured in an experiment are referred to as variables.

Independent variables -
This is the variable changed in order to observe the effect on the dependent variable.

Dependent variable -
The variable which depends on the change in the independent variable to alter.

Control variables -
These are the variables which need to be kept the same so that the effect of varying the independent variable is isolated.

Question 16

How are variables presented on graphs?

Answer 16

The dependent variable is commonly plotted on the y-axis. The independent variable is commonly plotted on the x-axis. It is assumed that the control variables are kept constant throughout.