Cambridge IGCSE Physics (0625) Syllabus

State the principle of conservation of energy.

Energy cannot be created or destroyed; it can only be transferred from one store or form to another. The total energy of a closed system is constant.

Define power and give its two equations.

Power is the rate of doing work or transferring energy. $$P = \frac{W}{t} = \frac{E}{t}$$ measured in watts ($\text{W}$); $1\ \text{W} = 1\ \text{J/s}$.

Give the equation for efficiency as a percentage.

$$\text{efficiency} = \frac{\text{useful energy output}}{\text{total energy input}} \times 100\%$$ equivalently using useful power output over total power input.

Define pressure and give its equation.

Pressure is force per unit area acting normal to a surface. $$p = \frac{F}{A}$$ measured in pascals ($\text{Pa}$); $1\ \text{Pa} = 1\ \text{N/m}^2$.

Give the equation for the pressure due to a column of liquid.

$$\Delta p = \rho g \Delta h$$ where $\rho$ is the liquid density, $g$ is gravitational field strength and $\Delta h$ is the depth/height of the column.

State the main points of the kinetic particle model for solids, liquids and gases.

Solids: particles closely packed, vibrate about fixed positions, fixed shape and volume. Liquids: close but free to move, fixed volume, no fixed shape. Gases: far apart, move rapidly and randomly, fill the container.

How does the kinetic model explain gas pressure?

Gas particles move randomly and collide with the container walls; each collision exerts a force. The total force per unit area from these collisions is the gas pressure.

State the relationship between pressure and volume of a fixed mass of gas at constant temperature (Boyle's law).

At constant temperature, pressure is inversely proportional to volume. $$pV = \text{constant} \quad p_1V_1 = p_2V_2$$

What happens to gas pressure (fixed volume) as temperature increases, in terms of particles?

Higher temperature means particles move faster with more kinetic energy, so they hit the walls harder and more often, increasing the pressure.

What is the relationship between Kelvin and Celsius temperature, and what is absolute zero?

$$T(\text{K}) = \theta(^\circ\text{C}) + 273$$ Absolute zero is $0\ \text{K} = -273\,^\circ\text{C}$, the temperature at which particles have minimum kinetic energy.

Define specific heat capacity and give its equation.

The energy needed to raise the temperature of $1\ \text{kg}$ of a substance by $1\,^\circ\text{C}$. $$E = mc\Delta\theta$$ where $c$ is specific heat capacity in $\text{J/(kg\,^\circ C)}$.

Define specific latent heat and give its equation.

The energy needed to change the state of $1\ \text{kg}$ of a substance with no temperature change. $$E = mL$$ where $L$ is the specific latent heat of fusion (melting) or vaporisation (boiling).

Compare the three methods of thermal energy transfer.

Conduction: through solids by particle vibration and free electrons, no net movement of matter. Convection: in fluids by circulating currents from density changes. Radiation: by infrared electromagnetic waves, needs no medium.

Which surfaces are best and worst emitters and absorbers of infrared radiation?

Dull, black surfaces are the best emitters and absorbers. Shiny, silver/white surfaces are the poorest emitters and absorbers (and the best reflectors).

State the equation for wave speed in terms of frequency and wavelength.

$$v = f\lambda$$ where $v$ is wave speed ($\text{m/s}$), $f$ is frequency ($\text{Hz}$) and $\lambda$ is wavelength ($\text{m}$).

What is the difference between transverse and longitudinal waves? Give an example of each.

In transverse waves the oscillation is perpendicular to the direction of energy transfer (e.g. light/water waves). In longitudinal waves the oscillation is parallel, with compressions and rarefactions (e.g. sound).

Define frequency and period of a wave, and state their relationship.

Frequency is the number of waves passing a point per second ($\text{Hz}$); period is the time for one complete wave. $$T = \frac{1}{f}$$

State the law of reflection.

The angle of incidence equals the angle of reflection ($i = r$), and the incident ray, reflected ray and normal all lie in the same plane.

What happens to a light ray's speed, wavelength and direction when it refracts into a denser medium?

It slows down, the wavelength decreases, and it bends towards the normal. Frequency stays the same.

State Snell's law and the definition of refractive index.

$$n = \frac{\sin i}{\sin r}$$ The refractive index also equals $n = \dfrac{c_{\text{vacuum}}}{c_{\text{medium}}}$, the ratio of speeds of light.

State the equation linking critical angle and refractive index, and define total internal reflection.

$$n = \frac{1}{\sin c}$$ Total internal reflection occurs when light in a denser medium hits the boundary at an angle greater than the critical angle $c$, so all light reflects back.

List the electromagnetic spectrum in order of increasing frequency.

Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. (Increasing frequency = decreasing wavelength.) All travel at $3\times10^{8}\ \text{m/s}$ in a vacuum.

Give one use each of microwaves, infrared and gamma rays.

Microwaves: satellite/mobile communication and cooking. Infrared: thermal imaging, remote controls, heaters. Gamma rays: sterilising equipment and treating cancer.

State the typical audible frequency range for humans and what determines loudness and pitch.

$$20\ \text{Hz} \text{ to } 20{,}000\ \text{Hz}$$ Pitch depends on frequency (higher frequency = higher pitch); loudness depends on amplitude (larger amplitude = louder).

Why does sound travel faster in solids than in gases, and can it travel through a vacuum?

Sound needs a medium because it is a vibration of particles; particles are closer in solids so vibrations pass on faster. It cannot travel through a vacuum (no particles).

What are the two types of electric charge and the rule of attraction/repulsion?

Positive and negative charge. Like charges repel; unlike charges attract. Objects become charged by transfer of electrons (negative).

Define electric current and state its equation in terms of charge.

Current is the rate of flow of electric charge. $$I = \frac{Q}{t}$$ measured in amperes ($\text{A}$); $1\ \text{A} = 1\ \text{C/s}$.

State Ohm's law and the equation linking voltage, current and resistance.

For an ohmic conductor at constant temperature, current is proportional to potential difference. $$V = IR$$ where $R$ is resistance in ohms ($\Omega$).

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 ($\text{V}$); $1\ \text{V} = 1\ \text{J/C}$.

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

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

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).

State the equations for electrical power.

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

Give the equation for electrical energy transferred.

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

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.

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.

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.

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.

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.

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.

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).

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.

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 $= A - Z$.

What are isotopes?

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

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.

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: $$^{A}_{Z}X \rightarrow\ ^{A}_{Z+1}Y + ^{0}_{-1}\beta$$

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.

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.

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.

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.

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.

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).

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.