SPM Questions: Transformer

In previous post,I gave u some SPM checklist instead of detailed notes about transformer. The reason i did that is to let u to do some work & revise what had been asked from the checklist.
Another reason bcoz i hate to spoon feed my student...

Usually..SPM questions are designed from those checklist. You can find these checklist in your text books under the column called learning outcome. If u have covered & understood everything that being asked in the outcome,i'm sure u can grab at least a 'B' for physics. However to get an A.. u need to do lots of extra exercises for P1,P2 & P3.
I know some of u hate to refer yr txt book..but trust me, those outcomes are your guidance..

Here i want to disucss some SPM passed year questions about transformer.
In my previous checklist, i asked u to state & relate the equation of ideal transformer.If u really understand the equation for ideal transformer, u shoudnt having prblem answering these questions. However your undrstanding on electricity must be strong enough..
Lets check'em out..

1.
SPM 2004




The important keyword in this questions is 'ideal transformer'.So in the xm i strongly advice u to underline this keyword. For ideal transformer, the output power is equal to input power.Since the bulb is having the same rating voltage & power, so it will produce same brightness. Answer: B







2.
(b) Figure 4.2 shows a circuit consisting of a transformer, an ammeter and two light bulbs. The ammeter reading is 0.5 A and both bulbs light up with normal brightness.












(i) What is the output voltage of the transformer?
(ii) Calculate the efficiency of the transformer?

i) Answer=12V
Explaination:
The bulbs are arranged in parallel. So the voltage across the bulbs are the same i.e 12V. The voltage across the bulb represents the output voltage of the transformer.
Basically this questions wanna test your basic understanding about electric circuit.

(ii) Calculate the efficiency of the transformer.
Efficiency = (Pout / Pin) x 100

Total Pout=2(24) =48W
Pin = VI =240 ( 0.5)= 120W

Eff= (48) / 120) } x 100
= 40%

Basically this questions wanna test your basic understanding about electric circuit. Please make sure u understand the parallel & series circuit calculation..