Paper 1A: multiple choice

Paper 1A is the multiple-choice part of Paper 1. Every question has four options, labelled A to D, and exactly one of them is correct. Each question earns one mark, and there is no penalty for a wrong answer, so no question should ever be left blank. A calculator and a clean copy of the data booklet are available, but the numbers are chosen so that the arithmetic takes seconds: most questions test whether you can choose the right physics, not whether you can push buttons.

The skill being tested is different from that of a written paper. In Paper 2 a sound method earns marks even when the final answer slips; in Paper 1A only the letter counts. That makes two habits essential: a fast, reliable route to the answer, and a check that the answer is not one of the carefully designed wrong options.

How the questions are built

A typical stem is three or four lines long: a short physical situation, sometimes a diagram, and one question. Most stems end with a direct question ("What is the tension in the cable?"). Some end mid-sentence, and the options complete it ("The internal energy of an ideal gas is"); those options start with a lower-case word and end with a full stop.

The options are not random. Each distractor is built by applying one plausible mistake to the correct method: forgetting the ½ in kinetic energy, using a diameter as a radius, leaving a temperature in degrees Celsius, not squaring a ratio. A student who makes that slip finds their answer waiting among the options, which is why "my answer is there, so it must be right" is not a safe check.

Stems also contain cue words that carry physics. "Negligible internal resistance" means the terminal pd equals the emf. "Released from rest" sets $u=0$. "Frictionless" or "in a vacuum" removes energy losses. "Ideal gas" allows $pV=nRT$ and means there are no intermolecular forces, so the internal energy is all kinetic. A question that seems to lack information often has the missing piece in one of these phrases.

A routine for every question

1. Read the whole stem, including the last line. Mark the quantity asked for and any cue words. Many marks are lost by answering a slightly different question, such as giving the distance when the displacement was asked for.

2. Cover the options and predict. Decide the physics and, for a calculation, get a value or at least a rough size. For a conceptual question, say in a few words what the answer should be.

3. Match and check. Find your prediction among the options. Then ask which slip each neighbouring option represents. If you can explain every distractor, you can be confident in the key.

4. If stuck, eliminate. Remove options with the wrong unit, the wrong direction, the wrong order of magnitude or an impossible limiting case. Guessing between two options is far better than guessing between four.

5. Mark and move on. If a question resists you for more than a couple of minutes, choose the best remaining option, mark the question, and return to it at the end.

Strategies that save time

Proportional reasoning

Many questions ask how a quantity changes when others are scaled: "The distance is doubled and the current halved. What is the new force?" There is no need to find any actual value. Write the relationship as a proportionality, then replace each variable with its scale factor.

For example, the power dissipated in a resistor connected to a fixed pd is $P={\displaystyle \frac{V^2}{R}}$, and $R={\displaystyle \frac{\rho L}{A}}$. A wire of the same material with twice the length and twice the diameter has $L\to 2L$ and $A\to 4A$ (area goes as diameter squared), so $R\to {\displaystyle \frac{2}{4}}R={\displaystyle \frac{R}{2}}$ and $P\to 2P$.

Units as a check and an eliminator

Every correct physics equation is homogeneous: both sides have the same units. When the options are algebraic expressions, working out the units of each one often leaves only one candidate. When the options are numbers, the unit of the quantity asked for confirms that the right equation has been used: an answer in ${\text{kg m s}}^{-1}$ is a momentum, not an energy.

The SI base units used for this are kg, m, s, A, K and mol. A newton is ${\text{kg m s}}^{-2}$, a joule is ${\text{kg m}}^2{\text{s}}^{-2}$ and a pascal is ${\text{kg m}}^{-1}{\text{s}}^{-2}$.

Estimation and orders of magnitude

When the options differ by factors of ten or more, a rough calculation with one-significant-figure numbers is enough. Estimation questions ("What is the order of magnitude of …?") expect you to know rough values of everyday quantities: a person has a mass of about 70 kg, a storey of a building is about 3 m high, the density of air is about 1 kg m⁻³ and of water 1000 kg m⁻³, a car on a motorway travels at about 30 m s⁻¹.

Limiting cases

An expression that is correct must behave sensibly at the extremes. If one option for the acceleration of a block on a frictionless slope at angle $\theta$ is $g\cos \theta$, setting $\theta =0$ gives an acceleration of $g$ on a horizontal surface, which is impossible: that option is wrong. The correct $g\sin \theta$ gives 0 on the flat and $g$ for a vertical drop. Testing an option at $\theta =0$, at ${90}^{\circ }$, at zero mass or at infinite resistance takes seconds.

Reading graphs

Graph questions test a small set of skills. For any graph, identify what the gradient represents and what the area under the line represents, and read the values from the axes with their units and prefixes.

For "Which graph shows …?" questions with four sketches, use the features in turn. Does the line pass through the origin? Is it straight or curved, and which way does it curve? Does it approach an asymptote? Is there a maximum, and where? Usually two of these features eliminate three options.

Statement questions

In a question with statements I, II and III, judge each statement on its own and write T or F beside it. Only then look at the options. Because the options are always the same four combinations, deciding that one statement is false removes two or three options at once. If statement II is false, only B ("I and III only") can be correct, as long as I and III are true.

Traps hidden in the distractors

The same slips appear in every theme. Learning to recognise them makes most distractors easy to reject.

Worked multiple-choice questions

Each question is followed by its answer, the reasoning, and the slip behind each distractor. Try each one before opening the solution.

Question 1: reading a velocity–time graph

Question 2: a collision

Question 3: an ideal gas and temperature

Question 4: a series and parallel circuit

Question 5: choosing an expression by its units

Question 6: field strength on another planet

Question 7: half-life

Question 8: a standing wave on a string

Question 9: an order-of-magnitude estimate

Question 10: statements about a pendulum

Using the whole paper well

Paper 1A rewards steady accuracy across all the questions more than brilliance on a few. The questions follow the order of the course, so the difficulty does not rise steadily: a hard question may be followed by an easy one. A question that takes far longer than the rest is still worth only one mark.

• Answer every question on the first pass, even with a provisional guess, so nothing is left blank if time runs short.

• Mark questions you are unsure of and return to them at the end with fresh eyes.

• Change an answer only when you find a definite error in your reasoning; a vague doubt is not a reason.

• Keep the data booklet open at the right page for each theme; checking a symbol or a constant is quicker than recalling it.

• For negative stems (questions with NOT in capitals), circle the word before answering.

Self-check

• To do:

  I can recognise the six formats of multiple-choice question and approach each one.

• To do:

  I can predict an answer before reading the options and explain the slip behind each distractor.

• To do:

  I can use proportional reasoning to find how a quantity changes when others are scaled.

• To do:

  I can use units to check an expression and eliminate options.

• To do:

  I can make a quick order-of-magnitude estimate using everyday values.

• To do:

  I can test an expression with a limiting case.

• To do:

  I can state what the gradient and the area represent for the common physics graphs.

• To do:

  I can judge I/II/III statements independently and use one false statement to eliminate options.

• To do:

  I can name the common distractor traps: factors of 2, wrong powers, inverted ratios, Celsius for kelvin, radius errors and missed details.