lesson
Resistance relates voltage and current
1 · Learn
Potential difference, measured in volts, describes energy transferred per unit charge between two points. Resistance, measured in ohms, relates potential difference and current through R = V/I for a stated operating point.
A component's resistance may change with conditions, such as temperature. Do not assume every component produces a straight-line current-voltage graph. A voltmeter measures between two points rather than replacing a series connection.
2 · Worked example
A supplied component has 6 V across it and current 0.5 A. Its resistance at that point is 6 ÷ 0.5 = 12 ohms.
3 · Your turn
Find resistance for 3 V and 0.25 A at the stated operating point.
Check your answer
12 ohms.
4 · Apply your learning
Calculate resistance from a supplied table and check whether it stays constant before claiming an ohmic relationship.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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