How to approach
Higher-order questions apply the formula to a described situation and ask you to explain or justify. Structure your answer: state, calculate, then interpret.
The method
- List what is given, with units.
- Choose the formula and rearrange for the unknown.
- Substitute with units on every line.
- Round to the correct significant figures.
Worked examples
Where marks are lost
Practise these
Try each formula above with your own numbers, showing every line. Bring anything you get stuck on to a one-to-one lesson.
Formulas you use for Electromagnetism calculations
These higher-order (KBAT) problems draw on the 3 relationships in Electromagnetism. None is printed in the exam, so recall each and write its symbols with units before substituting:
- Vp / Vs = Np / Ns, Transformer turns ratio
- VpIp = VsIs, Ideal transformer (power)
- efficiency = (VsIs)/(VpIp) × 100%, Transformer efficiency
A worked example, with units on every line
Using efficiency = (VsIs)/(VpIp) × 100% (Vs = secondary voltage (V); Is = secondary current (A); Vp = primary voltage (V); Ip = primary current (A)):
Output power VsIs = 48 W, input power VpIp = 60 W.
efficiency = (VsIs)/(VpIp) × 100% = (48 / 60) × 100% = 80%.
Where the marks are, and the common mistakes
In Paper 2, calculation marks are awarded line by line: the formula, the substitution with units, and the final answer with its unit and sensible significant figures. Watch this trap: It is output over input, so efficiency is always ≤ 100%.
Use power (V × I) values, not voltage alone. For higher-order (KBAT) items, expect multi-step problems that combine two relationships or ask you to rearrange before substituting.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)