BGCSE Physics (0571) flashcards
BGCSE Physics (0571) · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- SI unit of force
- The newton (N) is the force that gives a 1 kg mass an acceleration of 1 m/s². In base units, 1 N = 1 kg·m·s^-2.
- Derived unit of power
- The watt (W) equals one joule per second, or 1 kg·m²·s^-3. It measures the rate at which energy is transferred or work is done.
- Percentage error
- Calculated as the difference between a measured value and the accepted value, divided by the accepted value, then multiplied by 100. It shows accuracy.
- Independent variable
- The variable deliberately changed by the experimenter between trials. Its values are plotted on the horizontal axis when graphing results.
- Newton's second law
- The resultant force on a body equals its mass multiplied by its acceleration (F = ma). Force and acceleration point in the same direction.
- Principle of moments
- A body is in rotational equilibrium when the total clockwise moment about a pivot equals the total anticlockwise moment about the same pivot.
- Conservation of momentum
- In a closed system with no external resultant force, total momentum before an interaction equals total momentum after it. Momentum is mass times velocity.
- Kinetic energy formula
- Kinetic energy equals half the mass times the square of the speed (KE = ½mv²). Doubling speed quadruples kinetic energy.
- Pressure in a liquid
- Pressure at depth h in a liquid of density ρ is P = ρgh. It depends on depth and density, not on the shape of the container.
- Specific heat capacity
- The energy needed to raise the temperature of 1 kg of a substance by 1 K, given by E = mcΔθ. Water's value is about 4200 J/(kg·K).
- Specific latent heat
- The energy needed to change the state of 1 kg of a substance without changing its temperature, given by E = mL.
- Conduction versus convection
- Conduction transfers energy through particle collisions without bulk movement, mainly in solids. Convection transfers energy by density-driven fluid currents.
- Kelvin temperature conversion
- Absolute temperature in kelvin equals the Celsius temperature plus 273. Gas-law calculations must use kelvin, because 0 K is absolute zero.
- Wave speed equation
- Wave speed equals frequency multiplied by wavelength (v = fλ). Frequency is set by the source; speed depends on the medium.
- Longitudinal wave
- A wave whose oscillations are parallel to the direction of energy transfer, such as sound. It consists of compressions and rarefactions.
- Total internal reflection
- Occurs when light travels from a denser to a less dense medium and the angle of incidence exceeds the critical angle. No light refracts out.
- Refractive index
- For light crossing a boundary, refractive index n = sin i ÷ sin r, where angles are measured from the normal. It also equals speed in vacuum ÷ speed in medium.
- Ohm's law
- For a conductor at constant temperature, current is directly proportional to potential difference (V = IR). The resistance R stays constant.
- Resistance in parallel
- The combined resistance of parallel branches is less than the smallest branch resistance, because the total current splits between multiple paths.
- Electrical power formulas
- Power equals voltage times current (P = VI), which also equals I²R and V²/R. Energy transferred equals power multiplied by time.
- Electromagnetic induction
- A changing magnetic field through a conductor induces an emf. Faster change, stronger field or more turns give a larger induced emf.
- Brownian motion evidence
- Random jerky movement of smoke particles in air results from uneven collisions with fast-moving invisible air molecules, supporting the kinetic model.
- Isotopes
- Atoms of the same element with equal proton numbers but different neutron numbers. They have identical chemical properties but different masses.
- Half-life
- The time taken for half the unstable nuclei in a radioactive sample to decay. Activity and count rate also halve in each half-life.
- Alpha particle
- A helium nucleus of two protons and two neutrons, emitted in some radioactive decays. It is strongly ionising but stopped by paper or a few centimetres of air.
- Seasons on Earth
- Seasons arise because Earth's axis is tilted relative to its orbital plane, so each hemisphere receives sunlight at different angles during the year.
- Weight versus mass
- Mass is the quantity of matter in kilograms and is constant. Weight is the gravitational force on that mass (W = mg) and changes with local g.
- Redshift of galaxies
- Light from distant galaxies is shifted toward longer wavelengths, showing they recede. More distant galaxies recede faster, evidence the Universe expands.
- Random and systematic error
- Random errors scatter readings above and below the true value and are reduced by averaging. Systematic errors shift all readings the same way and need correction.
- Line of best fit
- A straight line drawn through a scatter graph so points are balanced above and below it. Its gradient gives the constant relating the two variables.
- Reducing timing error
- Measure the time for many oscillations, then divide by the number of oscillations. This reduces the effect of human reaction time on each reading.
- Direct proportionality graph
- A straight line passing through the origin shows the dependent variable is directly proportional to the independent variable. The gradient is the constant ratio.