Tuesday, September 27, 2011

Models of electricity

In today's lesson, there were some discussion about the various models of electricity.

(a) The conventional current model.

(b) The electron current model.

(c) Rueven's model of displacement.

(d) Mr Tan's model of EM radiation.

Dear students, it is quite obvious that the models (a) and (b) are well established models since Primary School.

However, models (a) and (b) does not seem to explain the electrical circuit effectively.

Then Rueven came to the rescue by introducing the concept that there are already alot of electrons present in the circuit. The battery acts like an energy source that moves a 'chain' of electrons or positive charges around the circuit.

However, Mr Tan questioned that if the wires are very long, will there be a time delay in the circuit? This poses a problem for Rueven's model because that will predict that there is a time delay before the lighting up of the circuit.

For your thinking caps.

Monday, September 5, 2011


When 2 battery is connected in series with a light bulb, the brightness of the bulb is as follows:
When a similar light bulb is connected in series, the brightness changes to the following:
What happens if the same light bulb is connected in parallel to the existing light bulb instead?


When 2 similar additional batteries are connected in parallel to the existing batteries, the brightness is as follows:
What happens if the 2 similar additional batteries is added in series to the original batteries instead? 


Friday, September 2, 2011

Parallel connections (Electricity WS page 13)

(a) Set up a single bulb circuit as shown below:
 (i) Connect two bulbs in series and add this combination as a branch in parallel with the single bulb circuit as shown below.
(ii) Is there a change in brightness of the single bulb when the second branch is connected? 

Combinations of Resistors (Electricity WS page 11)

Resistance (Electricity WS page 10)

Experiment - determine the resistance of a light bulb

Circuit Diagram

How is the resistance of the light bulb calculated ?

From the graph, it is obvious that there are 2 clear sections of graphs.
Explain why are there 2 clear sections.

The resistance of the light bulb can be determined by finding 
the gradient of the graph for the first section (dim). 

However, the resistance CANNOT be calculated by finding 
the gradient for the second section (bright). Explain why.  

Tuesday, August 30, 2011

What is inside a 12 volt battery ?


What is inside a D size RECHARGABLE battery ?


What is inside a 6 volt battery ?


Batteries come in AAA, AA, C and D sizes. Why not B?


What is in a 9 volt battery ?


What is a variable resistor or Rheostat ?

 Lab version

 TV tuner version

Saturday, August 27, 2011

How to measure the e.m.f. of a battery using a voltmeter ?

How to measure the resistance of a light bulb using an Ohmmeter ?

The resistance of the light bulb measured using this method is 2.6 ohms BUT
the resistance measured using the previous method with the lightbulb lighted up is 10 ohms.
Why is it so ?

How to measure the resistance of a light bulb ?

Is there a current when the light bulb does not light up ?

Wrong method of measuring potential difference using voltmeter:

Wrong method of measuring current using an ammeter:

How to measure the potential difference using a voltmeter ?

How to measure the current using an ammeter ?

Ammeter and Voltmeter