Practical Electricity Ii Notes

Coral Secondary School Secondary Two Physics 2009 Notes Name: _____________________________________________ (

)

Class: _________

Date: _________

Unit 7: Practical Electricity II Instructions to Students • • •

Step 1: Print Practical Electricity II notes Step 2: View the PowerPoint presentation and fill in the various blanks in the notes given. Step 3: Submit the completed notes to your physics teacher during the next lesson.

Learning Outcomes You should be able to, • state some electrical hazards and precautionary measures to ensure the safe use of electricity in the home.

7.1: Common Household Wiring •

Household wiring is wired as such, The live wire ( ____________ / ___________ ) is at a __________ voltage. This voltage may vary between ____________________ . In Singapore, this voltage is ____________ V. The earth wire ( _____________ / ___________ ) is at _________ V. No current flows in this wire under normal operation. It is connected to the ground.

The neutral wire ( ____________ / _____________ ) is at ________ V.

7.2: What is Short-circuiting? •

A short circuit is an accidental _____________________________________ between two nodes of an electrical circuit that are meant to be at different voltages

•

An example is the accidental connection of the ______________ and ______________ wires for Household Wiring

•

This causes an _____________________ of current in the circuit

7.3: Electrical Hazards Types of Hazards: y

Electric Shocks and Electrocution y

Occurs: When a person is injured or killed by _______________________ flowing through the

1 2009 Mr Chung T W David, Coral Secondary School

body. y y

Example: touching exposed live wire.

Electric Shocks and Electrocution y

Occurs:

A

short

circuit

occurs

causing

the

wire

to

be

overheated

and

__________________________. y

Example: Connecting too many electrical appliances to same output socket, causing a fire to break.

Possible Causes: y

Damaged Insulation y The wires of electrical appliances are insulated with ________________________________ such as rubber y Due to _________________________, the rubber can become damaged and the wires exposed.

y

Overheating of Cables y Refers to the unusually large amount of heat generated by ________________________ current flowing through the conducting wires. y _______________________ of a power point can generate a huge amount of heat too.

y

Damp Conditions y Wet conditions of the skin greatly reduce the _____________________________ of the skin. y Dry skin has a typical resistance of _____________ or more. However, it may drop _______________ when wet y With

a

voltage

of

240V,

a

deadly

current

of

0.23A

can

flow

through

the body

7.4: Electrical Safety y

General Guidelines: y y y y y y y

Never overload a socket Never use instruments to poke into an electrical socket Replace old wiring Do not wet electrical appliances, plugs or sockets Never use electrical gadgets in wet places Disconnect the appliance when cleaning it Call the electrician

2 2009 Mr Chung T W David, Coral Secondary School

y

Safety with Earthing y When a fault occurs, the earth wire will carry the _________________________________ directly. y This prevents the person who is in contact with the ground and touching the ‘live’ appliance to be electrocuted. y Appliances with ________________________________ are usually earthed.

y

Safety with Switches y Used to ________________________________________ when we are not operating the electrical appliance. y Must be fitted to the ______________________.

y

Safety by Fuses y Consist of a thin piece of copper wire, the fuse is given a current rating (i.e the _________________________ it can carry without melting). y When a fault occurs and the size of the current flow ___________________________________ of the fuse, the fuse will ‘blow’ (the fuse wire will melt, cutting off current flow). y Must be fitted to the ___________________.

y

Safety by Circuit Breakers y A special type of switch that ________________________________ electricity supply in a circuit if the flow of current becomes too large. y The circuit breaker can only be reset after the fault has been corrected. y ___________________________________ work like fuses but they ‘trip’ instead of ‘blowing’. y ___________________________________ detects small leakages in the earth wire and cut off the current in the live wire.

3 2009 Mr Chung T W David, Coral Secondary School