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P5 Science

The circuit tester is found in test pens. Its main purpose is to see if there is any current flowing through a circuit or any electrical components.
If there are any current, the bulb lights up and you would know that there is current flowing through the circuit or component.
So you would be careful not to touch the circuit or component in case you get an electric shock.



The wires are connected from the postive to the negative ends of the battery. This forms the series circuit. You need to know how to draw the wires for such a diagram in the exam.
For circuits with batteries connected in parallel, they give the same brightness irregardless of the
number of batteries in parallel.
The circuit with more number of batteries in parallel will last longer than the one with less batteries
in parallel.




The series circuit will be brighter than the parallel circuit. The current flowing through the series circuit is more than the current flowing through the parallel circuit. This is due to the large voltage drop across the bulb for the series circuit.

Both the circuits have the same brightness.
However, circuit A will last longer than circuit B.
Reason: Circuit A has only two bulbs so it uses less energy than circuit B.

                                3 pin plug
The fuse will break once the current exceeds the maximum that the wire can take. Therefore, the electricity will be cut off preventing electrocution.

This is a safety device to save consumers’ lives.
Usually the maximum amount of current is set at 13 ampere.

12. The diagram below shows a 3-pin plug.


a) Label the fuse in the plug above by drawing an arrow to it and label it as 'X'.[1]

b) What is the function of the fuse? [1]

    The fuse is a safety device that will break the circuit when the current exceeeds a certain amount.

c) Why is it dangerous to put too many of such plugs into one power outlet? [1]

    Too many plugs will draw too great a current which will cause overloading to the power outlet.
    This will cause the power outlet to shut down when the current drawn exceeds the limit.

Meaning of Kwh.
Kwh is the power rating of the electrical appliances.

It is used to calculate the amount of energy used by the appliances

for the time period that it was switched on.

Example:

An electric iron has a power rating of 5 Kwh.

Calculate the amount of energy used in 5 hours.

5 kwh X 5h = 25 kW

So if the electrical charges is $4 per kW, then,

the amount of money to pay for using the iron

would be $4 X 25KW = $100

Therefore, we have to pay $100 for using the iron for 5 hours.

Exam question on lamp and photosynthesis.

This purpose of this experiment is to show the relationship between light and

photosynthesis. The rate of photosynthesis is calculated by the number of bubbles

given out by the weed. Photosynthesis will produce oxygen and this gas is the bubbles

you see in the beaker.

The nearer the lamp to the beaker, the more bubbles will be produced.

This is because with more light, the rate of photosynthesis increases.

For a fair test, the voltage of the bulb/the type of plants/type of water must be kept the same.

Otherwise it would affect the validity of the results.

Questions for you to ponder.
1.  Why do we use parallel circuits for our home? What is the advantage over series circuit?

2.  How do we make the bulb light up for a longer time period for a series and a parallel circuit?
     Draw the circuit and think!

3.  How do we lower the current in a circuit without removing batteries or bulbs?
     Draw the circuit and think!


Simple electric motor:
http://www.youtube.com/watch?v=zOdboRYf1hM&feature=related

http://www.youtube.com/watch?v=it_Z7NdKgmY&NR=1

For concept relating to simple motor, just know the following:

1.  When a curren flows through a wire, it forms a magnetic field.

2.  The magnetic field will interact with another magnetic field and create a force.

3.  The force will push the wire and thus, there is motion.

You can try this at home!

Circuit X and Y are the same. You can move the wire to the left side and see that they are the same.
So Circuit X is not a short circuit.

The bulb will not light up in circuit B.
Circuit A and B are not the same. Circuit B is a short circuit. The current will flow in the chosen path as seen by the arrows because that path has the least resistance.


Review questions

1.  Draw a bulb and label its parts.

2. Draw a parallel circuit. (3 batteries and 1 bulb)

3. Draw a series circuit. (3 batteries and 1 bulb)

4. Which circuit will last longer? Why?

5. What are the advanatages of parallel circuits?

6. What are the advantages of series circuits?

7. Can pencil lead conduct electricity?

8. What is a fuse? How does it help you?