Myanmar Matriculation Physics flashcards

32 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 gives F = ma, with F in newtons, m in kilograms and a in m s⁻².

Conservation of momentum

When the net external force on a system is zero, total linear momentum stays constant. In a perfectly inelastic collision the bodies stick together and move with a common velocity.

Projectile range formula

For launch speed u at angle θ on level ground with no air resistance, the horizontal range is R = u² sin2θ/g, which is maximum at θ = 45°.

Centripetal force

The resultant force directed towards the centre of a circular path, of magnitude F = mv²/r = mω²r. It changes direction of motion, not speed.

Young modulus

The ratio of tensile stress to tensile strain within the elastic limit: E = (F/A)/(e/L). It is a property of the material and has units of pascals.

Principle of moments

For a body in rotational equilibrium, the sum of clockwise moments about any point equals the sum of anticlockwise moments about the same point; moment = force × perpendicular distance.

Linear expansivity

The fractional increase in length per unit rise in temperature: ΔL = αL₀Δθ. For isotropic solids, area expansivity β ≈ 2α and volume expansivity γ ≈ 3α.

Specific latent heat

The heat needed to change the state of unit mass of a substance at constant temperature: Q = mL. It is specific latent heat of fusion for melting and of vaporisation for boiling.

Ideal gas equation

For n moles of an ideal gas, pV = nRT, where R ≈ 8.31 J mol⁻¹ K⁻¹ and T is in kelvin. Equivalently pV = NkT with k ≈ 1.38 × 10⁻²³ J K⁻¹.

Root-mean-square speed

A measure of the typical molecular speed in a gas, c_rms = √(3RT/M), where M is the molar mass in kg mol⁻¹. It increases with the square root of absolute temperature.

First law of thermodynamics

The heat supplied to a system equals the increase in internal energy plus the work done by the system: Q = ΔU + W. For a gas at constant pressure, W = pΔV.

Carnot efficiency

The maximum possible efficiency of a heat engine operating between hot and cold reservoirs at kelvin temperatures T₁ and T₂: η = 1 − T₂/T₁. No real engine exceeds this.

Wave equation

For any wave, speed equals frequency multiplied by wavelength: v = fλ. Frequency is set by the source and does not change when the wave enters a new medium.

Stationary wave on a string

With both ends fixed, wavelengths are λ = 2L/n, giving frequencies f = nv/(2L). Nodes have zero displacement; adjacent nodes are separated by λ/2.

Constructive interference condition

Two waves from coherent sources reinforce when their path difference is a whole number of wavelengths, nλ, giving zero phase difference and maximum resultant amplitude.

Diffraction grating equation

Principal maxima occur where d sinθ = nλ, with d the slit spacing, θ the diffraction angle and n the order. Larger wavelengths diffract through larger angles.

Doppler effect

The change in observed frequency when source and observer move relative to each other. Approach raises the observed frequency; recession lowers it.

Speed of sound in air

About 330 to 340 m s⁻¹ at room temperature. It rises with temperature, is independent of pressure at constant temperature, and sound cannot travel through a vacuum.

Closed pipe harmonics

A pipe closed at one end resonates at f = (2n − 1)v/(4L), giving only odd harmonics. The fundamental corresponds to a quarter wavelength in the pipe.

Snell's law

For light crossing a boundary, n₁ sin i = n₂ sin r, with angles measured from the normal. Refractive index n = c/v, so light bends towards the normal entering a denser medium.

Critical angle

The angle of incidence in the denser medium for which the refracted ray grazes the boundary: sin C = n₂/n₁. Beyond it, total internal reflection occurs.

Thin lens formula

1/f = 1/u + 1/v, with distances measured from the lens and real-is-positive sign convention. Magnification m = v/u. Lens power P = 1/f with f in metres.

Two-slit fringe spacing

For Young's double-slit experiment, adjacent bright fringes are separated by x = λD/d, where D is slit-to-screen distance and d is slit separation.

Resistors in parallel

The reciprocal of the combined resistance equals the sum of reciprocals: 1/R = 1/R₁ + 1/R₂. The combined resistance is always less than the smallest individual resistance.

EMF and internal resistance

For a cell of emf ε and internal resistance r driving current I through external resistance R: ε = I(R + r). Terminal p.d. V = ε − Ir is less than the emf when current flows.

Capacitor energy

The energy stored in a charged capacitor is W = ½QV = ½CV² = Q²/(2C). Capacitors in parallel add directly; in series the reciprocals add.

Coulomb's law

The force between two point charges is F = kq₁q₂/r² with k ≈ 9 × 10⁹ N m² C⁻². The force is along the line joining the charges and acts both ways.

Faraday's law of induction

The induced emf equals the negative rate of change of magnetic flux linkage: ε = −N dΦ/dt. The minus sign expresses Lenz's law, opposing the change.

Photoelectric equation

Maximum kinetic energy of emitted photoelectrons: K_max = hf − W, where W is the work function. Emission occurs only above the threshold frequency f₀ = W/h.

de Broglie wavelength

A particle of momentum p has an associated wavelength λ = h/p. For an electron accelerated through voltage V, λ ≈ h/√(2meV).

Half-life

The time for half the nuclei in a radioactive sample to decay: T½ = ln2/λ ≈ 0.693/λ. After n half-lives the fraction remaining is (½)ⁿ.

Transistor current gain

For an npn transistor, emitter current equals base plus collector current: Iₑ = I_b + I_c. Current gain β = I_c/I_b, typically 50 to 300.