SPM Questions: Series & Parallel

Dear all,

..as for today i want to discuss passed SPM questions on series & parallel circuit. At the moment, I'll onlly discuss paper 1 questions.If u look carefully at the trend, most of the questions tried to test your students analystical skill..its not a direct maths calculations of current,voltage or resistance...

Now lets analyse the following SPM questions....

SPM 2004:

1. All the bulbs in the circuit below are identical?

Which of the following statements is true?

A Reading A1 >A2 >A3

B Reading A1 >A3 >A2 Answer: B

C Reading A2>A1>A3

D Reading A3 >A1 >A2

Explaination:
A1 is the biggest coz the current comes out directly from battery. Then this current will be divided into A2 & A3. Seems the bulbs are identical, so resistance at A2 is higher coz the branch is having 2 bulbs in a row. Flow of current will choose a route with smaller resistance, thus current in A3 is bigger.

2. The diagram shows a circuit containing four bulbs, A, B, C and D, which are lit at normal brightness. When a bulb is faulty, no current will flow through it. Which bulb, when faulty will cause all the other bulbs not to light up?

Ans: D

Explanation :Bulb A&C are parallel with B. If B blown up, current stil can flow thru A & C. If either A or C blown up, currrent can flow via B & D.

However, if D blown up, the circuit is open ( or its like jambatan runtuh) i.e no current can flow to negative terminal. Thus all light bulb will not light up.

3. The bulb in the circuit is lit at normal brightness when switches S1 and S2 are

closed.

Ans: A

If only S1 is closed, current will avoid higher resistance R, and follow the path with lower reistance through S1. So larger current will cross the bulb, thus the brightness will increase

If only S2 is closed, current has no choice, it still has to pass through the resistance R, amount of current will drop,thus brightness will decrease.

SPM:Analysing Series & Parallel Circuit

Sorry for not updating frequently last week ..i’ve been focusing on my tuition class..
one thing I can concluded, most of the student can now feel the SPM pressure
Hmm...cuti dah abis...so lets get back to business…

As promised, I’ll b discussing on analysing series & parallel circuit.
Hopefully u'v watched the previous video

2.3 Analysing Series & Parallel Circuit

In this subtopic u need to identify the differences between series & parallel circuit.

The differences are in terms of

i. amount of current passing through in each resistor
ii. voltage across each resistor
iii. and its total resistance

Ok, lets analyse series circuit..

In series circuit, current flows are equal through out the circuit.
I = I1 = I2

But, for voltage,

V=V1 + V2…

and for the total resistance in the bulb equals to,

R= R1 +R2 +R3

in series circuit… if one of the bulb blown up, the other bulb will
not light up.

Lets now examine parallel circuit..
What are the differences in Parallel Circuit compared to series circuit??

1. The arrangement looks different,usually parallel circuit has branches.

2. The amount of current passing through each bulb(resistor) are not equal
if each bulb has different resistance.

3. In terms of calculation,
The amount of current in the circuit can be represented by,
I= I1 + I2

The voltage across the bulb/resistor are equals to the voltage of the battery
V= V1 = V2

and the total resitance of the bulb can be calculated as,
1/R = 1/R1 + 1/R2

4. However, if one of the bulb has blown up, the others are still working

I'll discuss on passed SPM question on next post

SPM: Series & Parallel Circuit

I will discuss or may b post some questions on this subtopic soon...meanwhile y dont u watch this video & then look at your reference book.. cuti.. cuti jugak!!..tapi jgn langsung tak study :)!!

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