diff --git a/content/physics/final.md b/content/physics/final.md new file mode 100644 index 0000000..4646ab3 --- /dev/null +++ b/content/physics/final.md @@ -0,0 +1,101 @@ +> [!NOTE] A mass $m$ attached to a spring with constant $k$ oscillates on a frictionless surface. Derive an expression for the velocity $v$ as a function of displacement $x$. +> +> [!INFO]- +> Total mechanical energy in SHM is conserved: +> $$ +> E = \frac{1}{2}mv^2 + \frac{1}{2}kx^2 = \frac{1}{2}kA^2 +> $$ +> Solving for $v$: +> $$ +> v = \pm \sqrt{\frac{k}{m}(A^2 - x^2)} +> $$ + +> [!NOTE] A wave traveling along a rope is represented by $y(x,t) = 0.02\cos(40x - 600t)$. Determine the amplitude, wavelength, frequency, and speed of the wave. +> +> [!INFO]- +> The general wave form is $y = A\cos(kx - \omega t)$: +> - Amplitude $A = 0.02\ \mathrm{m}$ +> - Wave number $k = 40 \Rightarrow \lambda = \frac{2\pi}{k} = \frac{2\pi}{40} = 0.157\ \mathrm{m}$ +> - Angular frequency $\omega = 600 \Rightarrow f = \frac{\omega}{2\pi} = \frac{600}{2\pi} \approx 95.5\ \mathrm{Hz}$ +> - Wave speed $v = f\lambda = 95.5 \times 0.157 \approx 15\ \mathrm{m/s}$ + +> [!NOTE] In Young's double slit experiment, fringes are formed on a screen 1.2 m away using light of wavelength $600\ \text{nm}$. The slits are separated by $0.2\ \text{mm}$. Calculate the distance between adjacent bright fringes. +> +> [!INFO]- +> Fringe spacing is given by: +> $$ +> y = \frac{\lambda D}{d} = \frac{600 \times 10^{-9} \times 1.2}{0.2 \times 10^{-3}} = 3.6\ \text{mm} +> $$ + +> [!NOTE] A pendulum of length $0.5\ \mathrm{m}$ is displaced by a small angle. Determine its period and explain why amplitude does not affect the result. +> +> [!INFO]- +> The period is: +> $$ +> T = 2\pi\sqrt{\frac{L}{g}} = 2\pi\sqrt{\frac{0.5}{9.8}} \approx 1.41\ \mathrm{s} +> $$ +> In the small-angle approximation ($\theta < 10^\circ$), motion is independent of amplitude. + +> [!NOTE] A charged particle $q$ moves through a uniform electric field $E$. Derive the expression for the work done on the charge and its change in potential energy. +> +> [!INFO]- +> Work done: +> $$ +> W = qEd +> $$ +> Change in potential energy: +> $$ +> \Delta U = -qEd +> $$ +> since electric potential energy decreases when the charge moves in the direction of the field. + +> [!NOTE] A capacitor of $10\ \mu\mathrm{F}$ is charged to $5\ \mathrm{V}$. Calculate the energy stored in it. +> +> [!INFO]- +> $$ +> E = \frac{1}{2}CV^2 = \frac{1}{2} \cdot 10 \times 10^{-6} \cdot 25 = 1.25 \times 10^{-4}\ \mathrm{J} +> $$ + +> [!NOTE] A coil of wire rotates in a magnetic field. Use Faraday’s law to derive the expression for the induced emf. +> +> [!INFO]- +> Faraday’s law: +> $$ +> \mathcal{E} = -\frac{d\Phi}{dt} +> $$ +> Magnetic flux $\Phi = B A \cos(\omega t)$, so: +> $$ +> \mathcal{E} = B A \omega \sin(\omega t) +> $$ + +> [!NOTE] A wire carries a current of $3\ \mathrm{A}$ through a magnetic field of $0.5\ \mathrm{T}$ perpendicular to its length. The wire is $0.4\ \mathrm{m}$ long. Find the magnetic force. +> +> [!INFO]- +> $$ +> F = ILB\sin\theta = 3 \cdot 0.4 \cdot 0.5 \cdot 1 = 0.6\ \mathrm{N} +> $$ + +> [!NOTE] Explain the effect of damping on the amplitude-frequency graph of a driven harmonic oscillator. +> +> [!INFO]- +> Damping reduces the peak amplitude and shifts the resonant frequency slightly lower. Greater damping broadens the curve and lowers the quality factor $Q$. + +> [!NOTE] A mass-spring oscillator experiences light damping. Write the differential equation and general solution. +> +> [!INFO]- +> Equation: +> $$ +> m\ddot{x} + b\dot{x} + kx = 0 +> $$ +> Solution: +> $$ +> x(t) = A e^{-\gamma t} \cos(\omega' t + \phi) +> $$ +> where $\gamma = \frac{b}{2m}$ and $\omega' = \sqrt{\omega_0^2 - \gamma^2}$. + +> [!NOTE] A $0.2\ \mathrm{kg}$ object experiences a force due to gravity from Earth at a distance of $6.4 \times 10^6\ \mathrm{m}$. Calculate the force. +> +> [!INFO]- +> $$ +> F = G\frac{Mm}{r^2} = 6.67 \times 10^{-11} \cdot \frac{5.97 \times 10^{24} \cdot 0.2}{(6.4 \times 10^6)^2} \approx 1.96\ \mathrm{N} +> $$