Cameroon GCE A-Level Physics flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Newton's second law

The resultant force on a body equals the rate of change of its momentum. For constant mass this reduces to F = ma, with force in newtons and mass in kilograms.

Conservation of momentum

In any collision or explosion with no external resultant force, total momentum before equals total momentum after. Kinetic energy is conserved only in perfectly elastic collisions.

Centripetal acceleration

A body moving in a circle of radius r at speed v has acceleration v²/r directed toward the centre. The required force is mv²/r, supplied by tension, friction or gravity.

Elastic potential energy

Energy stored in a stretched or compressed spring obeying Hooke's law, given by ½Fx or ½kx², where x is the extension and k the spring constant.

Principle of moments

For a body in rotational equilibrium, the sum of clockwise moments about any point equals the sum of anticlockwise moments. Each moment is force times perpendicular distance from the pivot.

Progressive wave equation

For any wave, speed equals frequency times wavelength: v = fλ. Frequency is set by the source; speed and wavelength change when the wave enters a different medium.

Snell's law

When light passes between media, n₁ sin θ₁ = n₂ sin θ₂, where angles are measured from the normal. Refractive index n equals c/v for the medium.

Critical angle

The angle of incidence in the denser medium for which the refracted ray grazes the boundary at 90°. It satisfies sin c = 1/n, where n is the refractive index.

Diffraction grating equation

Bright maxima occur where d sin θ = nλ, with d the slit spacing and n the order. Sharp maxima arise because many slits superpose, unlike the broad double-slit fringes.

Stationary wave nodes

Points of zero displacement in a stationary wave, spaced half a wavelength apart. Antinodes, where displacement is maximum, lie midway between adjacent nodes.

Ohm's law

For an ohmic conductor at constant temperature, current is directly proportional to potential difference: V = IR. The resistance R is constant and measured in ohms.

Kirchhoff's second law

Around any closed loop in a circuit, the sum of e.m.f.s equals the sum of potential differences. It follows from conservation of energy in the electric field.

Capacitor discharge time constant

The product RC gives the time for charge to fall to about 37% of its initial value. Charge decays exponentially as Q = Q₀e^(−t/RC).

Fleming's left-hand rule

For a current-carrying conductor in a magnetic field, the thumb gives force, first finger field and second finger current, all mutually perpendicular. It predicts motor effect direction.

Faraday's law of induction

The induced e.m.f. in a circuit equals the rate of change of magnetic flux linkage through it. Lenz's law states the induced current opposes the change producing it.

Specific latent heat

The energy needed to change the state of one kilogram of a substance without changing its temperature, given by E = mL. For melting it is latent heat of fusion.

Ideal gas equation

For an ideal gas, pV = nRT, where n is the number of moles and R is 8.31 J mol⁻¹ K⁻¹. Temperature must always be expressed in kelvin.

First law of thermodynamics

The change in internal energy of a system equals heat supplied to it minus work done by it: ΔU = Q − W. Work done at constant pressure is pΔV.

Thermal conduction rate

Heat flow through a slab is dQ/dt = kAΔθ/L, where k is thermal conductivity, A the cross-sectional area, Δθ the temperature difference and L the thickness.

Carnot efficiency

The maximum possible efficiency of a heat engine operating between hot and cold reservoirs is 1 − T_cold/T_hot, with both temperatures measured in kelvin. No real engine exceeds it.

Photoelectric equation

The maximum kinetic energy of emitted electrons is hf − φ, where φ is the work function. Emission stops below the threshold frequency f₀, where hf₀ = φ.

de Broglie wavelength

Every particle has an associated wavelength λ = h/p, where h is Planck's constant and p its momentum. The effect is measurable for electrons but negligible for everyday objects.

Radioactive decay law

The number of undecayed nuclei falls exponentially: N = N₀e^(−λt), where λ is the decay constant. Activity A = λN also decays with the same constant.

Half-life and decay constant

Half-life is the time for half the nuclei in a sample to decay. It is related to the decay constant by t½ = ln 2/λ, approximately 0.693/λ.

Atomic energy levels

Electrons occupy discrete energy levels. A photon is emitted when an electron drops to a lower level, with energy hf equal to the difference between the levels.

Vernier caliper reading

Read the main scale at the zero of the vernier, then add the vernier division that aligns with a main-scale mark. A typical caliper reads to 0.1 mm.

Systematic versus random error

Systematic errors shift every reading in the same direction, such as a zero error. Random errors scatter readings unpredictably and are reduced by averaging repeats.

Combining percentage uncertainties

When quantities are multiplied or divided, add their percentage uncertainties. When a quantity is raised to a power n, multiply its percentage uncertainty by n.

Line of best fit

A straight line drawn through the centroid of plotted points, balancing points above and below. Its gradient and intercept are used to extract physical constants.

Logarithmic linearisation

If y = axⁿ, plotting log y against log x gives a straight line of gradient n and intercept log a. This turns a power law into a measurable straight-line graph.

Resolving a vector

To split a vector F at angle θ to the x-axis, use F cos θ horizontally and F sin θ vertically. Perpendicular components can be treated independently.

Op-amp inverting amplifier

With the input through R_in to the inverting terminal and feedback R_f, the voltage gain is −R_f/R_in. The negative sign shows the output is inverted.

Zener diode regulation

A Zener diode operated in reverse breakdown holds a nearly constant voltage across it. Placed across a load with a series resistor, it stabilises the supply voltage.