Are formulas given in the exam?

No. You must recall SPM Physics formulas.

Is a formula sheet given for these calculations?

No. SPM Physics (4531) provides no formula sheet, recall each formula and write units on every line.

What does the easy band mean?

Foundation items use the formula directly; marks come from showing the method.

Can a tutor mark my working?

Yes, in a one-to-one lesson the teacher checks each line and fixes the exact step that loses marks. From RM50/hr, paid trial available.

Electricity Calculations (Easy), SPM Physics

How to approach

These are direct plug-in problems: identify the formula and substitute. Get these automatic first.

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

Electric charge

Q = It

A current I = 2.0 A flows for t = 30 s. Q = It = 2.0 × 30 = 60 C.

Potential difference

V = W / Q

W = 60 J of energy is transferred by Q = 10 C of charge. V = W / Q = 60 / 10 = 6.0 V.

Ohm's law

V = IR (R = V / I)

A current I = 3.0 A flows through a resistor R = 4.0 Ω. V = IR = 3.0 × 4.0 = 12 V.

Resistors in series

R = R₁ + R₂ + …

Two resistors R₁ = 3 Ω and R₂ = 5 Ω are in series. R = R₁ + R₂ = 3 + 5 = 8 Ω.

Resistors in parallel

1/R = 1/R₁ + 1/R₂ + …

Two resistors R₁ = 6 Ω and R₂ = 3 Ω are in parallel. 1/R = 1/6 + 1/3 = 1/6 + 2/6 = 3/6 = 1/2, so R = 2 Ω.

Electromotive force

ε = IR + Ir = V + Ir

A cell of ε = 1.5 V and r = 1.0 Ω drives a current I = 0.5 A. V = ε − Ir = 1.5 − (0.5 × 1.0) = 1.0 V (terminal p.d.).

Electrical energy

E = VIt

A device runs at V = 12 V and I = 2.0 A for t = 60 s. E = VIt = 12 × 2.0 × 60 = 1440 J.

Electrical power

P = VI = I²R = V²/R

An appliance draws I = 5.0 A at V = 240 V. P = VI = 240 × 5.0 = 1200 W = 1.2 kW.

Where marks are lost

Skipping units, rounding too early, and writing only the final answer (which loses method marks in Paper 2).

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 Electricity calculations

These foundation problems draw on the 8 relationships in Electricity. None is printed in the exam, so recall each and write its symbols with units before substituting:

Q = It, Electric charge
V = W / Q, Potential difference
V = IR (R = V / I), Ohm's law
R = R₁ + R₂ + …, Resistors in series
1/R = 1/R₁ + 1/R₂ + …, Resistors in parallel
ε = IR + Ir = V + Ir, Electromotive force
E = VIt, Electrical energy
P = VI = I²R = V²/R, Electrical power

A worked example, with units on every line

Using Q = It (Q = electric charge (C); I = current (A); t = time (s)):

A current I = 2.0 A flows for t = 30 s.
Q = It = 2.0 × 30 = 60 C.

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: Time must be in seconds (convert minutes).

Charge is in coulombs. For foundation items, the numbers are direct, the marks are in showing the method, not just the answer.

Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)

Written by the spmphysics.com.my editorial team.· Updated 5 Sept 2026