Posterous theme by Cory Watilo

2.4 and 2.5

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2.4

24 November 2010

10:12
· 2.4 know some of the different ways in which electrical heating is used in a variety of domestic contexts
· Tell the person next to you…

...some electrical appliances in your house that change electrical energy directly into into heat energy

Answers
· Electric kettle
· Electric cooker/oven
· Electric hot shower
· Electric room heater (probably not in Thailand though!)
· Toaster
· Rice cooker
· Sandwich maker
· Hairdryer
· Etc…


· Note: Microwave cookers are not an example of electrical heating. They produce use electricity to produce microwaves which make the water molecules in food vibrate more and heat the food up.

2.5 answers

24 November 2010

10:12
· 2.5 understand that a current in a resistor results in the electrical transfer of energy and an increase in temperature

http://phet.colorado.edu/en/simulation/battery-resistor-circuit

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Answers
1. What happens to the rate of flow of electrons in the circuit? How do you know this?
· The rate of flow of electrons increases. The electrons are moving faster and turning the paddle wheel faster
2. What happens to the current in the circuit? How do you know this?
· The current also increases (current is the rate of flow of electrons!). The reading on the ammeter increases
· What happens to the temperature in the resistor? How do you know this?
· The temperature increases. The metal ions in the resistor vibrate faster and the reading on the temperature scale increases

2.3

2.3 answers

24 November 2010

10:12

• 2.3 describe the uses of insulation, double insulation, earthing, fuses and circuit breakers in a range of domestic appliances

Insulation
· Usually plastic

Double Insulation
· Wire to appliance is insulated
· Appliance casing is insulated
· Examples = computer monitor, plastic kettle, etc

Fuses
· http://www.youtube.com/watch?v=mk0p_zTaFzY
· Made of a thin piece of wire
· When current is too high the wire gets hot and melts
· The fuse "blows"
· UK plugs are fused

Earthing


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Electric toaster - circuit working normally

Live Neutral Earth
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Live Neutral Earth
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Live Neutral Earth
· A large current flows through the metal casing and down the Earth wire
· This melts/"blows" the fuse which breaks the circuit
· This prevents electrical fire

Circuit Breakers
· http://www.youtube.com/watch?v=mKJ5eTJBDyA
· RCD = Residual Current Device
· An RCD can break the circuit much faster than a fuse
· Prevents electric shock

2.3 Build a plug animation

25 November 2011

15:50
>

2.3 Plenary - harder questions

25 November 2011

15:51

PFY p.276, Q.8 a to d only
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(download)

(download)

2.2

2.2 Starter

24 November 2010

10:11
· My nomination for a Darwin award! http://www.darwinawards.com/
· What's the problem?
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Answer
· Water is a good conductor of electricity
· If the flip-flops flipped over, water would come into contact with the metal contacts in the extension lead and the fools in the pool would be electrocuted!

2.2 Starter 2

24 November 2010

10:11


>

Brainiac Electric Fence

2.2 answers

24 November 2010

10:11
· 2.2 recall the hazards of electricity including frayed cables, long cables, damaged plugs, water around sockets, and pushing metal objects into sockets
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(download)

2.25

2.25

25 November 2011

10:28

·         2.25 recall the potential dangers of electrostatic charges, eg when fuelling aircraft and tankers

Sparks caused by electrostatic discharge can be dangerous…

·        

...and impressive...

·        

...and stupid!

·        

 

Any volunteers?!

2.21 and 2.22

2.21 and 2.22

24 November 2010

10:40

·         2.21 recall that insulating materials can be charged by friction

·         2.22 explain that positive and negative electrostatic charges are produced on materials by the loss and gain of electrons

Instructions

·         Launch the application on this website:

http://phet.colorado.edu/en/simulation/balloons

 

 

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·         Rub the balloon on the sweater

·         Stick it on the wall

·         Charge a second balloon

·         Move it close to the first balloon

 

Questions

·         Why does the balloon get charged?  Take a screen shot to illustrate your answer

·         What happens when you move the balloons together?  Why?  Take a screen shot to illustrate your answer

2.22 to 2.24

 

 

2.22 Plenary Answer

30 November 2010

15:19

·         Note that the positive and negative charges balance for each picture

·         Therefore the total charge is zero in each situation

 

 

 

2.23 answers

24 November 2010

10:39

·         2.23 recall that there are forces of attraction between unlike charges and forces of repulsion between like charges

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Charge on ball A

Charge on ball B

Electrostatic Force

Positive

Negative

Attract

Positive

Positive

Repel

Negative

Positive

Attract

Negative

Negative

Repel

 

 

 

 

2.24

24 November 2010

10:39

·         2.24 explain electrostatic phenomena in terms of the movement of electrons

·         Charge up a student with the Van der Graph generator

·         Why does their hair stand on end? 

·         Can you explain this in terms of the movement of electrons?

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Explanation

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·         The electrons on each hair repel the electrons on every other hair

(download)

2.20 answers

2.20 answers

30 November 2010

14:43

·         2.20 identify common materials which are electrical conductors or insulators, including metals and plastics

Insulators

Conductors

Air

Metal

Plastic (used to encase electric wires)

Copper (used in wires)

Rubber (used to encase older plugs)

Brass (used in pins on plugs)

paper

Water (don't use your hair drier in the bath!)

Dry wood

Wet wood