ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Units and Prefixes

Updated on October 4, 2010

Units and Prefixes

In Physics we are often concerned with measuring. There is an international system of units that is used by scientists worldwide. This is known as the SI system, ( Systmem Internationale).

The base units in this system are:

Mass:- measured in Kilograms (kg)

 

Length:- measured in metres (m)

 

Time:- measured in seconds (s)

 

Current:- measured in amperes (amps.A)

 

Temperature:- measured in Kelvin (K)

 

Other quantities are also measured in particular units derived from the above.

 

Examples of these derived units are:

 

Speed:- measured in metres per second (m/s)

 

Force:- measured in newtons (N)

 

Energy:- measured in joules ( j )

 

Charge:- measured in coulombs (C)

 

Voltage:- measured in volts (V)

 

There are more units which I will introduce within other hubs as I go along.

 

Sometimes the size of the quantity being measured is much too large or small for the appropiate unit. In this situation we use multiples of the unit denoted by standard prefixes.

 

The common prefixes used at GCSE are:

 

 

Prefix       nano       micro       milli             kilo       mega       giga

Factor       10-9           10-6           10-3         I     103            106            109

Symbol       n            μ             m                k            M            G

 

 

 

In these cases the unit is multiplied by the factor,

for example:

 

5 milliamps (5mA) = 5 x 10-3 A

 

Now try the following:-

 

1. Convert 20km to m

 

2. How many amps is 30 μA?

 

3. What is 5000m in km?

 

4. Give 40000joules in MJ

 

Workings of examples

1. Convert 20km to m

On the calculator:

Multiply

   20 x the factor of the symbol km

= 20 x 103

= 20000m

If the case is that your calculator isn't handy it can be done by this alternative method:

 

 

20 = 2 x 101

   = 2 x 101 x 103 (remember when multiplying you add the indices)

   = 2 x 104 (104 means you have four zeros, therefore the answer is 20000)

   = 20000m

 

2. How many amps is 30 μA ?

On the calculator:

Multiply

   30 x the factor of the symbol μ

= 30 x 10-6

= 3 x 10-5

To do it manually without the calculator:

 

30 = 3 x 101

    = 3 x 101 x 10-6 (remember when multiplying you add the indices)

    = 1 + (-6) = -5 (therefore)

    = 3 x 10-5A

 

3. What is 5000m in km?

 

Remember there is 1000m in a km.

 

Quite simply you could divide by 1000 and get the answer as 5km.

 

On the Calculator:

 

Multiply

 

    5000 x the factor by the symbol m

= 5000 x 10-3

= 5km

 

To do it manually without the calculator:

 

5000 = 5 x 103

         = 5 x 103 x 10-3

         = 3 - 3 = 0 (therefore)

         = 5km

 

 

4. Give 40000joules in MJ

 

1 megajoule = 1 000 000 joules

 

On the Calculator:

Multiply

           40000 x the factor of the symbol j

 

In this case we don't have it in the above table, so we are going to divide by the factor MJ, which means our answer will be a fractional one, so it will have a negative power.

 

Divide

 

          40000 x the factor of the symbol M

             = 40000 ÷ 106

             = 4 x 104 ÷ 106

             = 0.04 MJ or 4 x 10-2 MJ

To do it manually without the calculator:

 

40000 = 4 x 104

          = 4 x 104 ÷ 106 ( when dividing remember to subtract the indices)

          = 4 - 6 = -2

          = 4 x 10-2 MJ

working

This website uses cookies

As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://corp.maven.io/privacy-policy

Show Details
Necessary
HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
LoginThis is necessary to sign in to the HubPages Service.
Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
AkismetThis is used to detect comment spam. (Privacy Policy)
HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
Features
Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
MavenThis supports the Maven widget and search functionality. (Privacy Policy)
Marketing
Google AdSenseThis is an ad network. (Privacy Policy)
Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
Index ExchangeThis is an ad network. (Privacy Policy)
SovrnThis is an ad network. (Privacy Policy)
Facebook AdsThis is an ad network. (Privacy Policy)
Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
AppNexusThis is an ad network. (Privacy Policy)
OpenxThis is an ad network. (Privacy Policy)
Rubicon ProjectThis is an ad network. (Privacy Policy)
TripleLiftThis is an ad network. (Privacy Policy)
Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
Statistics
Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
ClickscoThis is a data management platform studying reader behavior (Privacy Policy)