## Units and Formula **Skills**

This unit of work describes the recognition and sizes of the different SI units, how to convert prefixes and also how to manipulate basic formula.

This unit also describes skills when using physics equipment and when drawing and interpreting graphs in physics.

The skill of manipulating formula and units is essential in science. The following examples demonstrate the skill that is required at this level.

**Examples for units:**

Conversion from one unit to another involves multiplying or dividing. In most cases this is by a power of 10 and would mean moving the decimal point to the right for multiplication and to the left for division. If a name is given to the power of 10 then it is expected that we should use this name.

e.g. 200 mA to amps

Divide by 1000 by moving the decimal point 3 paces to the left.

200+ 1000 =0.2

=0.2 A

0.35V to millivolts

Multiply by 1000 by moving the decimal point 3 places to the right.

0.35x 1000 =350

= 350mV

Time is an exception as there are 60 seconds in one minute and 60 minutes in one hour.

e.g. Convert 2 hours and 20 minutes to minutes

2 hours x 60 = 120 minutes

120 minutes + 20 minutes = 140 minutes

**Examples for Formula**

Manipulation of formula involves algebra and the ability to divide and multiply letters as distinct from entire numbers.

Alternatively, divide each side of the formula by R:

Make I the subject of the formula from the formula V = I R

Use the formula triangle:

1. Cover the I

2. The outcome is V/R

3. The formula is

Example

To make **m** the subject of

Divide each side by:

Cancel all symbols of

Divide each side by g and cancel all like symbols

e.g. To equate two formulae:

to determine v using wavelength and period

Substitute frequency into the formula where there the inverse of the period

## Equipment Skills

**Common laboratory equipment that is used at this level:**

**Voltmeter**

This device is either analogue or digital and is used to measure the amount of electrical energy an electrical current carries. It is wired in parallel to a component with the positive terminal (red) being closest to the positive terminal of the power supply.

Ammeter

This device is either analogue or digital and is used to measure the flow of electrical current in an electrical circuit. It is wired in series to a circuit and the components in order for the electrical current to flow through the device.

Multimeter

This device is usually digital where it displays the data on an LCD screen in a numerical format. It has a multi purpose function and can measure a large number of different variables. The meter more commonly measures voltage, current and resistance but depending on the design it can measure for example the sizes of a number of electrical components, e.g. capacitance and transistor gain.

Oscilloscope

The oscilloscope is a multi functional electronic tool which can measure a variety of variables. The major purposes at this level would be to demonstrate the frequency of sound as well as both AC (alternating current) and DC (direct current) electricity.

Ticker timer

This device operates at a frequency of 50 Hz at a recommended voltage of 12V AC. It will operate at lower AC voltage settings but the dots produced on the ticker timer tape will not be as visible. This is because the timer will not imprint the tape with as

much force at the lower voltages. The dots produced by the ticker timer appear at a rate of 5 dots per second.This makes it possible to analyse the tape and produce both distance time and velocity time graphs.