Ohm's law

Each Ohm's law round has ten questions. In Standard, question 1 asks you to find potential difference using V = I R. Questions 2 and 3 rearrange the equation to find current and resistance. Questions 4 and 5 use current in milliamps or resistance in kilohms. Question 6 asks you to read a marked point on a straight I-V graph and find resistance. Question 7 asks you to identify a fixed resistor, filament lamp or diode from its graph. Question 8 checks where to connect the ammeter and voltmeter. Question 9 tests the rules for a series circuit. Question 10 gives decimal values for another V = I R calculation.

Challenge keeps the first seven question types. Question 8 asks for the total resistance of two series resistors. Question 9 asks for the potential difference across one resistor in a series circuit. Its method works out the total resistance and circuit current first. Question 10 asks whether each parallel branch has the same potential difference and whether total resistance is below the smallest branch resistance.

Choose an answer to see the method. Numerical answers include V, A or Ω. Circuit rules and component names have no unit. A correct answer is worth 10 points. Answer within 15 seconds for a 5-point speed bonus. In Standard, the question stays open after the bonus ends. In Challenge, an unanswered question locks at zero and counts as wrong. Practice mode removes the timer, and its Finish button ends the round early.

Use the potential difference equation page to enter values and check how the equation is rearranged. In the game, number keys 1 to 4 select an answer. Press Enter or choose Next to continue after reading the method. Your best score is saved on this device, with a separate best for Challenge.

Potential difference is the energy transferred per unit of charge between two points in a circuit. It is measured in volts (V). Current is measured in amperes (A), and resistance is measured in ohms (Ω). The equation is V = I × R: potential difference equals current multiplied by resistance. To find current, divide V by R. To find resistance, divide V by I. Keep the unit beside each value while you work.

Ohm's law describes an ohmic conductor, such as a fixed resistor, at a constant temperature. Its current rises in direct proportion to potential difference. On an I-V graph, this makes a straight line through the origin. In a filament lamp, the filament heats up as current increases. Its resistance rises and the graph bends. A diode lets current flow in one direction. It has a very high resistance in the reverse direction.

Convert milliamps to amps by dividing by 1,000. For example, 250 mA is 0.25 A. Convert kilohms to ohms by multiplying by 1,000, so 3 kΩ is 3,000 Ω. Convert before you use V = I R. A value that has the wrong unit can give an answer that is a thousand times too large or too small.

An ammeter measures current, so connect it in series with the component. A voltmeter measures potential difference across a component, so connect it in parallel. In a series circuit, the same current flows through each component. The resistance values add to give the total resistance. Potential differences across the components add to the supply. In a parallel circuit, each branch has the same potential difference. The total resistance is less than the smallest branch resistance. This round asks about that parallel rule in words.

The game follows AQA Physics 8463 sections 4.2.1.3, 4.2.1.4 and 4.2.2, plus AQA Combined Science 8464 sections 6.2.1.3, 6.2.1.4 and 6.2.2. Pearson Edexcel Physics 1PH0 and Combined Science 1SC0 include the topic in Topic 10, points 10.4, 10.7 and 10.12 to 10.18. OCR Gateway Physics A J249 covers P3.2a to P3.2m; Combined Science A J250 covers P3.2a to P3.2j. Read the AQA Physics specification, AQA Combined Science specification, Pearson Physics specification, Pearson Combined Science specification, OCR Physics A specification and OCR Combined Science A specification.

• Write down which quantity the question asks you to find.
• Use V = I R for potential difference, I = V ÷ R for current and R = V ÷ I for resistance.
• Convert mA to A or kΩ to Ω before substituting values.
• For resistance from a graph, divide the p.d. by the current at the marked point.
• Check both meter connections: ammeter in series, voltmeter in parallel.
• For series circuits, add resistance and check that voltage drops add to the supply.

Read the axis labels before choosing values from a graph. Potential difference is on the horizontal axis, and current is on the vertical axis. Keep the units with the values when you divide. If your answer is a thousand times too large or too small, check whether the question used mA or kΩ. The Equation Rearranger game gives more practice changing the subject of a physics equation.