Heat

Traps in Heat

• Leaves a quantity out of the formula
  Write the full formula and tick off each symbol as you substitute. Every symbol needs a value.
• Adds 273 to a temperature change
  A change of 10 °C is a change of 10 K. Add 273 only to actual temperatures (in gas laws), never to differences.
• Inverts a formula
  Write the defining equation in words first (density = mass per unit volume), then rearrange algebraically. Check units: kg/m³.
• Omits a term in Q = mcΔθ
  Q = m c Δθ where Δθ = final − initial. Latent heat: Q = mL with no temperature change.
• Uses everyday intuition instead of physics
  Name the law that applies (Newton's first law, Archimedes' principle, kinetic theory) and reason from it. If the option only 'feels' right, test it against the law.
• Mixes up a pair of similar physics terms
  Make a two-column table for each pair with one defining feature and an example. Underline the defining word in the stem before you look at the options.
• Picks a related law, device or effect with a different job
  Learn laws and devices as 'name → what it tells you' cards. Contrast neighbours: left-hand rule = motor force, right-hand rule = dynamo current, grip rule = field around a wire.
• Takes part of the condition as the whole answer
  Check whether the option is enough on its own. Equilibrium needs zero resultant force AND zero total moment; a complete explanation names every factor in the stem.
• Chooses a true but irrelevant statement
  Re-read the question word (why, which, what causes). A true fact that answers a different question is still wrong.
• Reverses a relationship or direction
  Write the relationship with an arrow or proportionality sign first (E ∝ f; R ∝ L; cooling a metal → R falls). Then check the option follows the same direction.
• Miscounts steps or makes a counting slip
  Count the steps explicitly on paper (list each half-life, each strand), then check the total.
• Uses Celsius temperatures in gas laws
  Gas laws need absolute temperature: T(K) = θ(°C) + 273. Convert every temperature before using a ratio.
• Puts a quantity or item in the wrong class
  Classify by the defining test: vector = has direction; charged radiation bends in a field; renewable = replaced naturally within a human lifetime.