Cambridge IGCSE Physics (0625) Flashcards

24 sample cards from the Physics (0625) deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Define potential difference (voltage) in terms of energy.

   The potential difference is the work done (energy transferred) per unit charge between two points. $$V = \frac{W}{Q}$$ measured in volts ($\text{V}$); $1\ \text{V} = 1\ \text{J/C}$.

2. Give the formulas for total resistance of resistors in series and in parallel.

   Series: $$R = R_1 + R_2 + \cdots$$ Parallel: $$\frac{1}{R} = \frac{1}{R_1} + \frac{1}{R_2} + \cdots$$

3. Compare current and voltage rules for series and parallel circuits.

   Series: current is the same everywhere; voltage is shared (adds up). Parallel: voltage is the same across each branch; current is shared (adds up to the total).

4. State the equations for electrical power.

   $$P = IV = I^{2}R = \frac{V^{2}}{R}$$ measured in watts ($\text{W}$).

5. Give the equation for electrical energy transferred.

   $$E = IVt = Pt$$ measured in joules ($\text{J}$). For domestic billing, energy is measured in kilowatt-hours ($\text{kWh}$).

6. What is the purpose of a fuse and where is it placed in a UK plug?

   A fuse is a thin wire that melts and breaks the circuit if the current exceeds a safe value, preventing fire. It is placed in the live wire so the appliance is isolated.

7. Describe the function of the earth wire and double insulation.

   The earth wire connects the metal casing to earth, providing a low-resistance path so a fault current blows the fuse, preventing electric shock. Double insulation (plastic casing) means no earth wire is needed.

8. State the pattern of the magnetic field around a bar magnet and the law of poles.

   Field lines run from north pole to south pole outside the magnet, closest together where the field is strongest. Like poles repel, unlike poles attract.

9. Describe the magnetic field around a current-carrying straight wire and how to find its direction.

   Concentric circles around the wire. Direction is given by the right-hand grip rule: thumb points along the (conventional) current, fingers curl in the field direction.

10. State the principle of an electromagnetic motor (motor effect).

    A current-carrying conductor in a magnetic field experiences a force (motor effect). Fleming's left-hand rule gives its direction; reversing current or field reverses the force.

11. State Faraday's law of electromagnetic induction.

    When a conductor cuts magnetic field lines (or the flux through a coil changes), an e.m.f. is induced. The size of the induced e.m.f. increases with faster movement, stronger field and more turns.

12. Give the transformer equation relating turns and voltages.

    $$\frac{V_p}{V_s} = \frac{N_p}{N_s}$$ where $p$ = primary and $s$ = secondary. For an ideal transformer $V_pI_p = V_sI_s$ (power is conserved).

13. Describe the nuclear model of the atom (charges and locations).

    A small, dense, positively charged nucleus of protons and neutrons at the centre, surrounded by negative electrons in orbits. Most of the atom is empty space.

14. Define proton number $Z$ and nucleon number $A$, and write nuclide notation.

    Proton (atomic) number $Z$ = number of protons; nucleon (mass) number $A$ = protons + neutrons. A nuclide is written $$^{A}_{Z}X$$ Number of neutrons $= A - Z$.

15. What are isotopes?

    Atoms of the same element (same proton number $Z$) but with different numbers of neutrons, so they have different nucleon numbers $A$.

16. Compare alpha, beta and gamma radiation in terms of nature and penetration.

    Alpha ($\alpha$): helium nucleus ($^{4}_{2}\text{He}$), stopped by paper, most ionising. Beta ($\beta$): fast electron, stopped by thin aluminium. Gamma ($\gamma$): electromagnetic wave, reduced by thick lead, least ionising.

17. Write the change in a nucleus during alpha decay and beta-minus decay.

    Alpha decay: $$^{A}_{Z}X \rightarrow\ ^{A-4}_{Z-2}Y + ^{4}_{2}\alpha$$ Beta-minus decay: $$^{A}_{Z}X \rightarrow\ ^{A}_{Z+1}Y + ^{0}_{-1}\beta$$

18. Define the half-life of a radioactive isotope.

    The half-life is the average time taken for half the radioactive (unstable) nuclei in a sample to decay, or for the activity to fall to half its initial value.

19. What is background radiation? Give two sources.

    Low-level ionising radiation always present in the environment. Sources include radon gas from rocks, cosmic rays from space, medical X-rays, and food/drink.

20. List the order of the planets from the Sun and distinguish rocky from gaseous planets.

    Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The inner four (Mercury–Mars) are small rocky planets; the outer four are large gas/ice giants.

21. Why do planets orbit the Sun, and how does orbital speed relate to distance?

    The Sun's gravitational attraction provides the centripetal force keeping planets in orbit. Planets further from the Sun move more slowly and have longer orbital periods.

22. What is the source of the Sun's energy?

    Nuclear fusion in the core, where hydrogen nuclei fuse to form helium, releasing huge amounts of energy. The Sun is a stable main-sequence star.

23. What is meant by redshift and what does it tell us about the Universe?

    Light from distant galaxies is shifted to longer (redder) wavelengths, showing they are moving away from us. More distant galaxies show greater redshift, evidence that the Universe is expanding (supporting the Big Bang).

24. Outline the life cycle of a star similar in mass to the Sun.

    Nebula → protostar → stable main-sequence star → red giant → planetary nebula → white dwarf, which cools to become a black dwarf.

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