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.